Computer Networks from Scratch | Mohammad Adly | Skillshare

Computer Networks from Scratch

Mohammad Adly, Ph. D. Computer Networks

Computer Networks from Scratch

Mohammad Adly, Ph. D. Computer Networks

Play Speed
  • 0.5x
  • 1x (Normal)
  • 1.25x
  • 1.5x
  • 2x
20 Lessons (3h 29m)
    • 1. What is a Computer Network?

    • 2. Computer Networks Topologies

    • 3. Computer Networks Categories

    • 4. Computer Networks Devices and Services

    • 5. Computer Networks Transmission Media

    • 6. ISO/OSI Model (7 Layers)

    • 7. Application, Presentation, and Session Layers

    • 8. Transport and Network Layers

    • 9. Data Link and Physical Layers

    • 10. ISO/OSI Model in Action

    • 11. Introduction to Computer Networks Protocols

    • 12. IP Protocol

    • 13. TCP and UDP Protocols

    • 14. Application Protocols

    • 15. TCP/IP Tools

    • 16. Wireless Networks Benefits

    • 17. Wireless Networks Types

    • 18. Wireless Networks Protocols

    • 19. Wireless Networks Devices

    • 20. Wireless Networks Drawbacks

  • --
  • Beginner level
  • Intermediate level
  • Advanced level
  • All levels
  • Beg/Int level
  • Int/Adv level

Community Generated

The level is determined by a majority opinion of students who have reviewed this class. The teacher's recommendation is shown until at least 5 student responses are collected.





About This Class

This class enables the IT and CS undergraduate students as well as professionals to understand the basics of computer networks including the benefits, typologies, and categories. The class simplifies the technical terms used in such field and facilitates moving through any further courses in the same domain

Meet Your Teacher

Teacher Profile Image

Mohammad Adly

Ph. D. Computer Networks


Hello, I'm Mohammad.

See full profile

Related Skills

Technology Data Science

Class Ratings

Expectations Met?
  • Exceeded!
  • Yes
  • Somewhat
  • Not really
Reviews Archive

In October 2018, we updated our review system to improve the way we collect feedback. Below are the reviews written before that update.

Your creative journey starts here.

  • Unlimited access to every class
  • Supportive online creative community
  • Learn offline with Skillshare’s app

Why Join Skillshare?

Take award-winning Skillshare Original Classes

Each class has short lessons, hands-on projects

Your membership supports Skillshare teachers

Learn From Anywhere

Take classes on the go with the Skillshare app. Stream or download to watch on the plane, the subway, or wherever you learn best.



1. What is a Computer Network?: welcome to our course. Let's start our course by answering this question. What is a computer letter? The definition of a computer network is simply as follows its a group off computers that are sometimes called hosts or notes and a group off computer peripherals that are all connected together via transmission media and some connecting devices. All of these elements form what we call a computer network. The types off computers have change it. Nowadays, we have laptops, tablets, smart mobile phones. We used tohave only personal computers or PCs that were also called desktop computers. Nowadays, we have others that are mobile and that can transfer and send and receive information over the network. Every single human can now be connected toe a computer network through PC's through laptops , tablets, smart mobile phones and, through water school the embedded systems inside, some off the electrical or mechanical machines. Yes, some of these machines can send and transfer and exchange data and information between each other transparently without the interference or the interaction off the human users. In order to offer a certain service for him with his minimal or with the least interaction from his side. This concept is known as Internet of things. Internet of things allows things machines to exchange information between each other in order to offer a certain service required by human users. The peripherals that can be connected to a computer are simply the hardware, the printers, the scanners, the storage media. All of these are called preference. These peripherals can also be connected to a computer network as senders and as receivers off information and orders from the computer users to execute something that he wants to be done. Printers, scanners and storage media can be directly connected to the computer network and be part of it toe act as sources and destinations off data being transferred. If we have a look inside a cloud computing or a data center, we can see some servers, some storage devices and some terminals that are used for managing and configuration off the devices inside this cloud, computing or data centers. All of these can be seen as connected through transmission media in a local network inside the center to offer a certain type of service required by the computer users, either infrastructure as a service or platform as a service or software, the service This newly introduced concept is known as the cloud computing concept, and that is mainly depending on computer networks. The transmission media. The transmission media used by a computer network can be the wired media, the cables or the wireless media using air as the transmission media, the wired media. The cables can be made off copper or can be made off. Fiber optic copper cables can either be co axial cables or twisted pair cables and in turn , that twisted pair cables can either be shielded cables or unshielded cables, either STP Sheila Twisted pair or you TP cables. Unshielded twisted pack. The fiber optic cables does not transmit electricity. It transmits light light moves in the fiber optic cables in the form off single mode light or multi mode light. The difference between single mode and multi mode is in the capacity and the speed off this cable, the wireless transmission media using air depends mainly on a specified frequency band and a certain area or distance off coverage. Every wireless technology differs from the other in the utilized frequency band, and they utilized area off coverage or the distance between the sender and receiver covered by this wireless network. Every wireless technology has a named band and a limited and known area off coverage. Toe transfer data across the benefit off connecting computers through a network mainly lies in resources trading resources, either hardware or software. Hardware resources like the computers, reference printers, scanners and other preference that can be connected to computers can also be shared through a computer network. One copy off the printer can serve 10 users instead, off buying 10 copies off printers. To serve these 10 users we hear save money, Safe Coast, save effort and also safe time through one copy of the hardware that can be shared too many users. The storage media can act in the same way one storage media can store for several users. The processing Power one supercomputing multi processor server can help in the processing off several computers. If shared through the network, the software resources that can be shared through the network can be a file that can be copied and pasted over the letter that can be shared between two devices over the network. It can be a database database off students that can be shared through professors, database off employees shared through the company accounting the portmanteau calculate their salaries and their bonuses. Applications also can be shared over the Net. Turkey. They are also software Resource is an example of an application. The simplest example is a game, a game that can be played by several users over the letter. This is an application that is used over the network by several users and in real time services. Services that can be offered over the network can be the browsing service, searching for information over the network and exchanging email messages across the users off the writer. These are the most commonly used services. Also establishing voice, schools and video conferences over the network are one off the common uses off a computer network. Inside and Enterprise, the basic network elements are mainly the end devices. These are the communicating devices, the senders and the receivers, the sources and the distillations off information. These are the target off the rhetoric to communicate with each other. Other devices exist inside the network as intermediate devices as connecting devices such as the switches, the routers and the excess points. Such devices are not meant to be sources or destinations off information, but they are acting as transferring entities for the information toe help or facility it that moving process off these information across the Net. The medium used through the information network specifies how these devices are connected. Are they connected in a wired way or in a wireless way? Are they going to use the cables or the air as the media off connection messages? The messages are the information that are needed to be traveling through the letter needed to be transferred needed to be communicated from the sender toe. The receiver messages are also that or get off the existence off computer network. We established computer network to transfer messages across the end devices through human users. The protocols off a computer network rules and governs how the information is transferred. The protocols are the agreements and are the standards that every device either connecting were and device should follow and should take care off when dealing with information inside the computer network. Hopefully, we have now answered what a computer network is. Thank you 2. Computer Networks Topologies: Now let us explore the computer networks. Apologies. What is a computer network? Topology? What is meant by the word topology? The word apology means the arrangement the structure off the various elements off a computer network, which depicts both physically and logically. The physical topology is the physical way the network is wired, how the computers are connected to each other. The logical topology identifies the way messages are sent, how to send a message and how a message moves from one machine toe. Another. That apology can be explained in a physical and logical essences. The basic network topology is the most common. The most well known apologies are the point, the point topology, the bus topology, the ring topology, the star topology and the mashed apology. Now we will explore one by one off them. The point upon topology is just a link, a physical link, either cable or a wireless thing that is connecting two points. Or it can be a logical link, logical point to point connection that is passing through an eyes be Internet service provider, connecting a source no to a destination. Note. It's a dedicated link, a dedicated media toe. Connect these two nodes. Only. The bus topology is a single cable that functions as a bus as a shared media as a backbone . Computers attached or tap with an interface connected to this bus. This bus this shared media Easter belated by Terminators, and the computers are connected through connectors, either in T piece or in y peas. We can see here that apology off the connection and the connectors, the Teepees, the Wye Peace and the Terminator that resides at the end off the musk ape. The advantages off the bus topology is that it is simple to design, very simple to design and very easy to install. It is also inexpensive due to using the co exhale cables as the shared media and using the B and C connectors boy in it nil concealment, connectors. These type of connectors are very cheap, inexpensive and very efficient in working that this advantages off this must apology is the security. This the apology allows for sniffing every message. Passing from one machine to another can be sniffed by any other machine on the same bus. This means that the privacy of the message, the confidentiality of the message can be tackled any time it's passing the media. The bus topology is slow during high traffic. If high traffic is introduced to this topology, the speed off the whole network goes down, leading to poor performance. The most apology allows for collisions. Collisions means that assume that two machines are sending their messages at the same second. Both off messages will exist on the shared media at the same second as well, so both messages will collide with each other. Here is how collision happens. Zeros and ones off. Both messages will no longer be zeros and ones. They will be something else that is called jam signals, something that is that has no meaning. That is meaningless, which means that we have to re transmit both messages again, which means poor performance and slower network and many times off. Retransmission. The SEC. The third topology is the ring to polish drink. Apology, basically is a cable in the form of a ring, as shown that connects one Noto, another toe, another to form a drink. The ends are attached to each other in the form of a ring. Messages traveled through this ring, always in the same direction, always in one direction, either clockwise or anti clockwise. The messages are transmitted in frames that circulates all the machines, which allows for sniffing. Obviously, the ring topology allows for acknowledgement. The sun frames circulates back toe the source of the message toe, acknowledge that transmission has been done and to set the frame free for another machine to put its message on the same frame to be sent as well. The advantages off drink topology is that it is simple. Also designed to design, easy to install. It's very inexpensive due to using the co axial cables and the B and C connectors. It's it looks like the bus topology in this site. This advantage is off the ring Topology is that the entire network fails. If only one machine fails. Because it breaks the ring, it stops the messages from circulation. So the whole network rail's. If only one machine member of this network fails to connect the expansion off this network or reconfiguration effects operation, imagine that you want to expand this network. You have to stop one of the machines, add another machine, you will have to break the rink, and the circulation off messages will stop for some time until you finish the expansion or reconfiguration, then the operation is restored during the policies. Also slow for big numbers off machines. If a big number off machine is installed in ring topology, this leads to slow network and poor performance. Also the start apology. This is the most well known the most common topology that is used nowadays. In that works, The star topology depends on connecting each station directly to a central device as seen in the edge. The connection is like a number off point to point links. Each machine looks like being connected in a point to point link toe this central device. This central device can be a hub or switch nowadays switches arm or commonly used than hops . The switch is a more recent technology and more secure device. The switch allows for no sniffing to be done, while the hub allows for sniffing to be done on the natural. The switch allows for no collision to take place while they have allows for collisions to take place. So the switches, now that most used technologies in collect in connecting a number of machines to each other in a local area network or Ln the advantages off the store topology is that the network is not affected if one machine fails or if the network is reconfigured. The network expansion is very simple. You just add the new machine, so the switch or the hub without affecting the performers or the operation off the whole letter. Troubleshooting is easy. You can easily identify the failing machine from the switch. You can easily identify where the problem or where the broken cable exists. The disadvantages off the store topology is that if the central device fails, all the network fails, and this is very rare toe happen. This is not common toe happen. Central devices are so far reliable. The mashed apology means that every device is connected toe the other devices through a separate link. It connects all devices with multiple partners. So between each device and another, you can find multiple partners that can connect such device to the other one. It offers a very high redundancy in connection, which means very high reliability, which is part off the security off the network. The number of cables equals toe the number off connected nodes multiplied by the same number, minus one and then divided by two. This equation is used to calculate the number of cables used in any meshed apology, knowing the number off connected notes. The advantages off the match topology is that it is very high, full tolerant. It allows for broken cables to exist because any broken cable can be substituted with another path for a good cable to exist. It's very secure, since it has high availability and availability is part of the security, so it is very secure. From this point of view, the disadvantages off the mashed apology is that it is expensive due to using hot, big number off cables and you, too, offering high redundancy. This leads toe very high coast. Sometimes by this we come to the end off the computer networks, the policies, and we hope that we clarified the most known and common basic computer network. Topology is Thank you 3. Computer Networks Categories: let's now categorize computer networks and know the categories off a computer networks. What could it be categorizing? Computer networks can be according toe the transmission mode off this network, the geographical area covered by this network or the administration type applied to this network. The transmission mode can either be simplex half duplex or full duplex in a simplex network . The data always flow from the same source, toe the same destination over the media. Off the snatcher, the source of data is always the same, and the destination is always the same as well. The direction of data is always from the same source toe the same destination in a simplex network in 1/2 duplex network. The source can be a destination, and the destination can be the source of data. Both can send to each other, but at different time intervals, which means the source can send to the distinction at Time t one and after a certain period of time at time, T to the destination can send toe the source back in a full duplex network. Each station can be the source and the destination at any time. The direction off data all the time is bi directional. The source and registration can be any machine at any time in a full duplex. Better, the signalling mode off the network is also one off the terminologies we need to know in our course. What is the meaning Off Days Band and Broadbent based band is one signal that flows at a certain time on the network media In a digital four. It is a digital local signal flowing. For example, as in this image from the workstation toe, the modem inside the room were inside the building or inside the local area network. This biz man signal gets to be modulated after modulation this best bet. Then signal becomes a broadband signal that can traveling a long distance from the modem till the central office off. That PST and all the public service telephone network in broadband divides the network media into multiple challenge. This allows for several signals to exist. The broadband signal is anna look modulated signal. While the base band is digital categorizing. Networks according to geographical area can lead toe having local area network or land or wider network, or when, as you can see in the image A When or wider genital can be formed off different lands connected through when link simply it. When can be two connected lands through a large geographical area. The land is a group of computers connected in small geographical area. Small means less than three kilometers, or just only group of computers connected inside one building one company, one entity having a group of computers, telephones, televisions, network printers and others connected through one switch. This is a very simple land. Lands are used to share files and services inside this company or building. It's a communication off high speed, which means that the speed off this land can be one gigabit per second or even more according to the speed off the switch. The land is always under the administrative control off its owners. It's designed the land is under the user. Administrative control technology is used to establish a land can be Ethernet or token drink the wide area network, or when is a group of computers connected in large geographical area? Large means more than three kilometers. Compared to a land the when is low speed, it is in the range off megabit per second speed, the when it under the administration. Off the eyes be Internet service provider, since the links connecting the win belongs to this eyes be. The technology is used to establish a when can be the dial up the eyes, the end or the integrated services Digital entered the DSL or the digital subscriber line X 25 frame relay or the most recent? Which is the A t M, the asynchronous transfer mode. These are all technologies that are used to connect computers through A when the most common used now for connecting computers to the Internet are, of course, the DSL technology, either synchronous or asynchronous. The ascent, categorizing an utter according to administration type, leads Toa having peer to peer network or client server network in a peer to peer network. Each host provide and consume network services. Each host has the same administrative privileges. Each user sitting on a machine is the administrator of this machine and shares whatever services he likes and also receives whatever requests he likes and access any file he would like to access according to the permissions off this peer to peer, not or perforce in a client server network, some hosts are assigned server roads. What is the meaning of a surface? The server is a superior computer superior in hardware and software. The hardware of a server is big. Big means big storage, big network connection, big memory and also powerful processing. The software off the server is a server operating system, which is powerful enough to run such hardware. Servers provide network resources to hosts. Each server exists on the network for the purpose. Off a certain service, a server can be Web server, mail server, Deanna Server or other server, which means that this machine server dedicated for a certain service other hosts that are not servers are assigned client rules Clients consume the network resources clients son requests to servers and receives the reply off such requests from the servers. So they are recipients, so they are consumers on the network, according to administration type. From the point of view off centralization in the peer to peer network, no central server exists in a client server. Old client machines connect to a central server and sends requests to it from the storage point off view. Each machine share files equally with each other. But in the client server network, old files and folders are stored on dedicated storage on the surf. Klein's only exist such wife from the Coast point off you peer to peer networks are expensive, while the client server networks are expensive because off the coast of the service, the coast of the hardware and the coast off the license off the software required for the server to run the peer to peer network is scalable in the range off home or small office. While the client server scale is in a medium or large enterprise scale, the operating systems existing on a peer to peer network is the client operating systems. Only the operating systems existing on a client server are the server breathing system, such as Lennox or Microsoft Windows Server Toe handle multiple requests from that lines. Hopefully, we have now introduced the different categories off computer networks. Thank you 4. Computer Networks Devices and Services: this lecture is about the computer networks devices and the computer network services. The networks devices can be the network interface scored the Nick court, the help, the switch, the excess point or the routers. The network interface scored is the cord connected toe the mother board from one side and connected toe the network cable from the other side. It's the network adapter. It's an interface between the PC and the network cable. It resides inside the mother board off a PC. It establishes the communication with the PC through the device driver. Any hardware connected toe, The mother board must have a software driver to facilitate the management, the configuration and the performance off this piece off hardware. This snake court contains transmitter and contains a receiver at the same time, It's called a transceiver, which is a mixture between the transmitter and the receiver. The Natural Interface Court can be wired, which means that can be connected to a cable or wireless with an antenna connected to the air interface and can be both wired and wireless at the same time. The hub, the hub, shares the frames between machines, a frame of data that is send by machine. A tow machine B is shared among machines C, D and E and all the other machines inside the hub to reach its destination from A to B. This means that the hub is a very good chance for sniffing. The hub is composed of a number of ports to connect several machines. Each machine is connected to the help through a port. Inside this hub, the hub works with full duplex communication. Each machine can send or receive at the same time and at any time on the hub. The hub can connect machines with mixture off speeds ranging from 10 Maiga 100 Mega one, Giga and even Mawr. Inside the hub they help allows. Four collisions is under can send. Meanwhile, another sender wants to send, which means that both signals from Sender A and Sunder Be can meet at the same time inside the hub, forming a jam signal that has no meaning. And at this point off time, Thunder A and sender B has to re send their messages. Collisions mean hub is one collision to mean The hub is one broadcast. The mean collisions make the network slow and congested. Collisions happen when two senders wont to send at the same time and their signals ad as zeros and ones on the media to form something that is neither zero nor one that is a dream signal. And then both machines have to resend their messages. Tow, avoid collisions. Machines connected through a hub follows an algorithm that s cold. Cisma city, Cisma City stands for carrier says multiple excess collision detection. If a machine wants to send a message over the media, that is the hub, it first must sense the carrier. Is there another carrier on the media? If there is another carry on the media than this machine that wants to send has to wait for some time If unfortunately to machines like here in the image such as A and E want to send at the same time, they both sense the media. They both find the media empty at the same time. They both 10% at the same time. This is that point of time. That collision happens. This is the point of time. We're both signals meat on the media, forming something that is meaningless. What happens when collision happens? Collision detection takes place and then a back off algorithm makes a wait for a certain time before resending its message that has collided with another message and the waits for another period of time to rescind its measure message that has collided with another message. This off course makes all the machines lose some time and makes the network slower and leads to poor performance. For this letter. Collision is something that we do not like toe happen on the network. The switch. The switch is one off the network devices that is a more recent technology than they have it. Forwards and filters frames the switch forwards frames among the ports that want to send to the ports that want to receive only. So the switch allows for no collision, and the switch allows for knows living. The switch is better in performance and this, which is a more secure technology than they happen. The switch works off course with full duplex communication. Each machine can send and receive at the same time. The switch can work with mixture off speeds ranging from hundreds off megabits per second toe gigabits per seconds. This which is one broadcast, the mean but each port inside this which is a separate collision to meet. That's why, once more, the switch allows for no collisions and allows for no sniffing the excess point. This is a wireless device that connects machines wirelessly inside a land. A local area network, it transmits frames in the air media and also receives frames in the air media. It links the world this port off the network, toe the wire, the infrastructure the antenna send and receive wirelessly. Meanwhile, the excess point itself is connected toe an Ethernet cable, a wired interface that connects the wireless part off the network toe the wired infrastructure off the network. The excess point is one broadcast domain. The excess point off course is one collision domain and allows for collision. Meanwhile, there is an algorithm that can be followed tow. Avoid collisions in the air media, which is called Cisma. See a carrier sense multiple access. Collision avoidance. The rotors. The rotors is the device that redirects packets between networks. It works based on routing table that is toward inside it or built inside it either static or dynamic. The router divides the network in tow. Several broadcast domains. Each port in the rotor is a separate broadcast to me, the router device in the network also into several collision the ways each port in the router is a separate collision. To me, the services that can be offered inside the land can't be file sharing that of this raring or application sharing. This is a form off software resources centralization that can be offered through Ln Ln can share files, data basis and any applications among the users off the land applications can be games that can be played by the users existing on this land. Also, the land can share several hardware preference, like the printer, the scanner, even the process er of a certain machine can be shared toe another machine to use. Even the storage inside the land can be shared through a storage server that every other machine can access. As a client, the wen services differ from the land services. The one services can be Web service, which can allow for Web browsing, Web searching or accessing the social media. The one services can offer e mail services that can be exchanged among the users over a When and let's recall hear that the Internet is a When is the largest one over the Internet . The end. The Internet is the network of networks. It's compromising all the lands in the world. The Internet is a very big wide area network. The Internet offers the service off file transfers through sharing or file transfer protocols. The Internet can offer voice schools and can offer video conferencing. Also, any small when connecting to lands can offer the same services, voice, schools and videoconferencing among the users existing on this matter. Now we have explored the devices, the services off a computer network, Thank you. 5. Computer Networks Transmission Media: Now it's time to know more about the transmission media that are used in computer networks . The media can be wired media using cables or wireless media using the network. A single network, as you can see in this image, can be composed off a wire port and a wireless part, most of them in the same network and connected to each other. The water and media uses cables either made of copper or made off fiber optic copper cables can be co axial or twisted pair cables that twisted pair cables themselves can be shielded or unshielded. She'll that twister pair STP or unshielded twisted pair you tp cables. The fiber optic cables can use the light signals in single mode, such as the laser mode or in multi mode. The wireless media wants more uses the air interface to transmit and receive signals. The co axial cables, as you can see in the images composed off several ports that is ended with an outer jacket . It's high capacity cables used for video transfer. There are two types off Excel cables, Fico Excel cables or thick nut and think, oh, excel cables or thin that the thick ones are half inch damage. And there who is stunned? Based five. Which means, for example, the speed is 10 megabits per second, and the maximum distance that can be covered is 500 meters. The think wechsel cable code is 10 base two, which means the speed is 10 megabits per second and the maximum distance covered these 200 meters. The diameter of the Thinker Excel cable is quarter inch, while the diameter of the Fico Excel cable is half inch wolf cables. Use the B and C connectors. The shield. A twisted pair. STP cables are protected through this field against the electromagnetic interference with other electrical signals. The SDP cables are hard to install. Do you to exist? Existence off this shielding STP cables use the registration Jack RJ 45 which is in the middle of this image. The crimp Ertl used on the bottom left is used toe. Connect such cables to the registration jack by pressing on the cable to enter inside this , restrict registration drag and be connected. So the networks afterwards, the U TP cables or the unshielded twisted pair cables are the most commonly used types. They are easy to install, less expensive. Do you know the absence off shielding? But they are susceptible to electromagnetic interference with other electrical signals. Also, due to the absence of shielding you, TP uses the registration jack 45 connected RG 45 uses the same crimp er tool toe. Connect the registration right through the cables that twisting off the UT P cable determines its capacity. For example, in this image, cable A has less twisting than cable be. This makes cable a off less capacity than cable. Be cable is Cat three UT P cable while cable be escaped. Five You TP cable and both are made of the same. Material only differs in the number off twists per meter. Cable A can hold up to 10 megabits per second. Meanwhile, cable we can hold up 200 megabit per second due to the extra numbering number off twisting . For this type off cable the categories off you TP cables are in the stable cat one or category one is four. Voice only. Telephone wires get five speed reaches up 200 megabits per second, which is the first Internet get five e reaches upto one gigabit per second Category six ranges from one gigabit 10 gigabit per second, which is the gigabit Ethernet. The pins, the terminals off the you tippy cables are in the colors shown in the image at the right brown, white, brown, orange, wide, blue, blue, white, orange, green, white, green. They range from 1 to 8 from bottom to top. Terminal number one and terminal number two, as shown on the image on the left, are used for transmission. Terminal number three and terminal number six are used for receiving. This is the standard off the UT P cape. The fiber optic cables transmit light, not electricity. It's faster than the twisted pair and the co axial and faster than the copper cables. In general, it sends data as light policies over glass. Medium. It is free off electromagnetic interference. Since the pulse is our light, not electricity, it's expensive, and it is hard to install this start off cables can be used in the submarine connections connecting continents to each other and countries to each other over the Internet. Fiber off the cables are more secure. They are less susceptible to sniffing over such type off cables. The fiber optic cables are composed off core carriers for the signals. This score is made off. Plastic or glass cladding surrounding the core maintains the signal in the center of the core. Even if the cable bends sheeting that is surrounding the cladding protects the cladding and the core both through the outer jacket. Also, the fiber optic cables molds are the single mode or multi mode single mode transfer data through the core using a single light ray. The core diameter is around nine. Micro's supports a large amount of data larger than the multi mode cable. The cable length can extend a greater distance than the multi moved. The multi mode cable transfers the data through the core, using multiple light rays. The core diameter is about 15 microns. The cable length is limited in distance compared to single mode, which means that the single most cable is a more recent technology and a more expensive technology than the multi move. The advantages off the fiber optic cable is it is totally immune to the E. M I electromagnetic interference. Highly resistance to sniffing or eavesdropping support extremely high data transfer rate. This makes it suitable for submarine cables. It allows greater cable distance without the need toe repeaters, the disadvantages. It is very expensive. It is very difficult to work with and needs very talented to conditions to deal with. Let's talk about the wireless media using the air interface the WiFi, which is the abbreviation off the wireless fidelity. It uses the frequencies off 2.4 gigahertz or five gigahertz. The standards off the WiFi are a B, G or N. The WiFi uses the excess point previously demonstrated in this course to connect the devices wirelessly and to connect the wireless part of the network toe the wild port. When you go wireless, you gain more mobility. You gain more flexibility, for the device is connected wirelessly, but you lose security. Wireless networks are less secure than the wired networks. They are susceptible to sniffing, since the media used is merely the air, which is exposed to all the users off the network. By this, we have demonstrated the computer networks, transmission media. Thank you 6. ISO/OSI Model (7 Layers): welcome to the second section off or course section. Addressing the eyes OS I model the very famous seven layers this section is explaining, demonstrating these seven layers and their functionalities. The eyes always I model, as we can see, is an output off the Aiso International Standardisation Organization. This output is named the OS I model Open system interconnection model. It's a primary architectural model. Ford Networks. It was developed in 1983. It's only a group off concepts. This means that the model does not specify a certain hardware or software to exist. It is a group of concepts. It's a conceptual model. Debt specifies the functionalities that that are needed to be done to transmit data from a certain source to a certain destination over the Internet. It specifies how data can be sent or received. Either hope to help, which means I either from the machine do this. Which do they routed and so forth, step by step, or sending and receiving data and to end, which means sending and receiving data between a source that is in Malaysia and a destination that is in Egypt, which means that both are trying to send correct data reliable data from a certain source on the Internet to a certain destination over the Internet world. WHITE The benefits off dividing this model into layers are a lot. Dividing the network communication process into layers allows for easier troubleshooting arouse for for easier design and easier specifications for each layer Toby set inside this model. It allows for multiple vendors to build their products either software or hardware products based on the same standard model that is called the O. S. I. Many vendors. Giant companies can establish hardware components or software components based on this eyes OS I model, and these components can interact and can send and receive data to each other. Since they are based on the same mother. The OS I model the Open System Interconnection model, designed by the Aiso International Standardisation Organization. Various types of networks with various types of hardware and software can communicate, which means, for example, that Windows machines can communicate with Lennox machines. IBM machines can't communicate with apple machines. Machines on copper cables can communicate with machines on fiber optic cables. All of these, since based on the same model, can communicate with each other and concerned and transmit data with each other. Built on the same standard model that is the OS I model developed by the eyes. The layer separation makes it easier to change the design off one layer without affecting the other layers without affecting the upper or the lower layer. The design, the functionality off each layer can be made better can be change it without affecting the seven layers as a whole. We just take into consideration what each layer can take from the upper and deliver toe the lower. When changing the design off this layer, layers interact with each other while sending each layer passes. The data downwards from the seventh toe, the first while receiving data is past upwards from the first to the sudden death and the headers off each layer is added while you are sending and it is removed while you are receiving. This is the interaction with the layers that allows, and that gives us, at the end better communication between hosts and destinations over the Internet. This is the diagram showing the seven layers we should know by heart these names, and we should know by heart that we are counting from bottom toe up. The first layer is the physical. It's always layer number one. The second is the data link. The third is the network, the fourth is the transport the fifth, The fifth is the session. The six is the presentation and the seventh is the application layer. We always count from down to up each layer if summarized in one sentence. In this light, the application is responsible for communication between the application itself as a software and the network processes lying in the layers down. The presentation is responsible off data representation. The session is responsible for managing the session in the inter host communication process , starting ending and managing the session. Wild communication. The transport is responsible off and toe and connections either reliable or best effort delivery. The network is responsible for addressing and routing, finding the best path for the data to go through. Based on the address off each machine, the datalink is responsible for accessing the media and avoiding collisions. The physical is responsible for the binary transmission off ones and zeros representing the data in electrical form or in light. For if we are going to use the fiber optic cables, natural protocols that were based upon the eyes. Always I model are a lot, but we are here focusing on four protocols that were used and we're comin and were extensively known to be protocols based on the eyes. Always. I model the Net Berry Protocol, the I p X SP expert, to call the apple toe protocol, and we end by the TCP I people to cool the standard protocol of the Internet that will be address the next section in dictates. Then at very protocol, not very stands. Four Net buyers extended user interface. It was a land protocol that work only overland and do not work over a wide area networks. It has limited performance, not a good performance, and it's now almost obsolete protocols. It does not exist a lot or not common to be existing over the world, but this was a lamb protocol based on the eyes. Always. Simon. The second protocol is the I P X SPX that was vendor oriented that was designed by one off the company's working in hardware and software. It will standard based on the eyes or eyesight, and it supported transmission of data over when, But it also had a disadvantage, it row back that it was or rented too much towards its founder. It had poor performance if used with other vendors. If you use this protocol with another vendor, not with the vendor that made this protocol and designed it, you will have a very poor performance or you're on your network and your machines. Apple talk is a standard protocol based on the eyes OS I. It supports when, and it supports data transmission over routers. But it is very oriented towards its vendors, and it also has the same grow back and the same this advantage off poor performance if used with other vendors. It worked greatly with the same vendors that made this protocol and made the machines using it. But it had a very poor performance. If you change it, the machines to be made with other vendor using this protocol, the TCP I p, the worthless sippy I P stands for transmission control protocol, Internet protocol. It's a standard protocol. It supports when and supports Toby track transmitting data over rotors. It is not vendor oriented, and this is a very big advantage in TCP I P. That makes it growing and developed and always the standard protocol for transmission over the Internet. Nowadays, the D C. P i. P is the most widely used protocol over the Internet. The TCP I p is completely and entirely mapped toe the OS I layers. The S I seven layers are completely mab to the TCP I p protocols. As you can see in this diagram, it is not a 1 to 1 mapping. It's a group toe one mapping between the OS I'll ears and the TCP I P. Protocol. Now, we had a good idea about the eyes. Always. I model in this lecture. Thank you. 7. Application, Presentation, and Session Layers: this lecture covers the top three layers off the eyes. Always, I model the application. The presentation and the session layers. Layer seven, layer six and layer five the application layer. It is the interface between the user, the human users and the rest off the seven layers. It's an interface between the user and the lower layers off the I saw Asai Modern. That translates and tries to make it easier for the lower layers toe. Execute the orders and the requirements given by the user toe the network. The application rail is responsible for the preparation off data for each service. Each service on the Internet requires data to be prepared in a certain format toe appear in a certain way. For example, the Web browser at lets the data appear in the form off text images and hyperlinks. Another service, like the file transfer service the FTP, requires later to appear in the form off solid files. Another service, like the email service, requires data to appear in the form of messages. The preparation off data for each of these service is responsibility off the application layer. The application layer is the goal off the seven layers toe perform. End to end communication on both sides between the application layer at the sender and the application layer at the receiver. This is the logical connection that needs to be established between the sender and the receiver, as if the application Lear here is talking directly to the application layer there, as if there were no other layers interfering the end to end communication on both sides. Off the thunder and the receiver is the goal off the seven layers providing and toe and communication between the application layer here and the application layer. There is the reason for the existence off these seven years. The application layer the seventh layer in the eyes. Always I model is the layer where the software application three sites where the program you are dealing with as a user exists and takes from you the data that needs to be sent over the network and passes toe the lower six layers, starting from presentation and ending toe the physical. The application layer is the actual layer that sends the requests at the sending process and the actual air that receives the reply at the receiving process. It's the layer that takes the request from the user passes to deliver layers and receives the reply, arriving from the lower layers and presenting it to the users in a readable and understandable. For example, protocols that work at the application layer are the following http hypertext transfer protocol. This is for Web services f d p file transfer protocol. This is for transferring files between sources and stations over the Net s MTP. The simple mail transfer protocol This is for the mail exchange over the Internet. Pop three is the post office protocol. SMTP is for exchanging email messages Among the mail servers. Pop three is for exchanging email between the client and the mail server. I'm APP is instant message access. Protocol is also for exchanging email messages between the client and the mail server. Top three allows for downloading email messages I met is only for accessing and reading email messages. Tell nut and as a search protocols are four. Allowing for remote administration between decline that exists in a certain machine over the Internet and a server that exists maybe two or three countries away on the Internet and the user sitting on the client software X as if sitting on the keyboard and the mouse connected directly to the server machine and can do whatever he likes on the server machine through this stele nut application, the domain name system or the domain name server. The Deanna's is the protocol responsible for resolving the domain names in tow I P addresses and vice versa. It's the protocol that allows for writing www dot at yahoo dot com and then connecting toe a certain machine with the I P edges corresponding to this domain name server, the RTP Protocol. The rial time protocol is responsible for transferring data that are really time data such as the audio and the video. Really, time transfer off data has certain requirements for certain data that are delay sensitive and not sensitive to losses in the same way that they are sensitive today. So the rail time protocol, which is somehow a new protocol, is responsible for transferring data off such kind. The presentation layer, or layers number six, is responsible for the common representation off data between any source and any destination. It is responsible off presenting the data to the application when receiving and receiving the data from the application. When Sunday. In a certain form that can be understandable by both the source and the destination. It provides the transformation of data. It supports a standardized application interface at the sore side and at the destination side, it is responsible off coding the data syntax. It's responsible off coding the data, according to a certain Syntex. That is understandable. Bible to the source and the destination. It is responsible for the encryption at this underside and the decryption at the receiver side off the data being transmitted. It is responsible off the compression at this underside and the decompression at the receiver side off, the data being transmitted between the source and the destination. The social layer, or layer number five is those about managing the session starting by establishing decision in itself, managing the session while it is running and up controlling the session while it is transferring data and at the end of the session it is responsible of how the session can be terminated safely. If we look at this diagram, we can see that the social layer sons some data that is like some data, we or like some sentences we use between each other's as human to start conversation. If you say to someone, I'd like to send you something and he says, Sounds good. This is a request that is replied by an acknowledgment. This is an establishing to a connection. These two messages are the responsibility off the session layers to transmit end toe acknowledge at the beginning of the session at the end of the session, when you send your data completely and entirely, you say toe the receiver, thank you, and he acknowledges you by the sentence, you are welcome. This is closing the session safely and closing the connection safely off course. In between these two messages in between these two diagrams, the session can be stopped and can be restarted and can be resumed at a certain point of time. The flow of data can be controlled and can be slowed down and can be set to a faster speed . All of these functionalities are the responsibility off the session layers. It is responsible off managing the session as a whole from the establishment by some handshaking between the sender and the receiver, till determination by some handshaking and acknowledgement between the same sender and the receiver and through controlling the session in between. While the data is being transferred between the sender and the receiver off the data, the social layer makes sure the connection is active during the session and make sure that it is not falling down. It's is responsible off securing the commission. It is responsible off the synchronization of the dialogue, the synchronization off the sending and the receiving off data. It is responsible off checking for the connection failure if existing during the session, which leads to losing data and which leads to slowing down the data transfer process. It's responsible for re connection if there is a cut off during the sending off the data or during the data transmission, Re connection or resuming the session is the responsibility off the session layer. It's responsible off terminating the communication at the end of the session. After all, the later has bean received by the receiver. The social layer defines the note. Communication order and timing, order and timing are the core off the synchronization off the data. Sending this is the responsibility off the session layer as well. The three layers, the application, the presentation and the session are very closely connected they are very related in function to each other. That's why they form the application layer in the TCP i p. If we have a look at the TCP I P protocol suit, we can say we can see that the application layer the presentation layer the session layer in the eyes OS I model are all compact and link it together in one layer in the d c p i p that is called the application layer in the d. C p i p. This makes the disip E I P only four layers, not several years. Those three layers are responsible off content for mating are responsible off for mating and representing and preparing the data being sent from the center to the receiver. It's preparing for the network. Proofs is preparing for addressing preparing for routing and preparing for establishing the connection for the data to be transmitted through they network lairs that lies down starting from layer four until the physical layer in the eyes Os. I'm on by this. We have introduced those important Fleer airs. Thank you 8. Transport and Network Layers: this lecture handles the transport and that will Claire's. These are the two main layers that concern the network specialist. The network engineers. The Transport Layer Layer number four. It organizes data into segments. The word segment is the unit off data at the transport layer at Layer number four, where it is a packet at layer number three and a frame at layer number two, and bits and bytes at the physical layer. Layer number one. The transport layer is responsible for the end toe end delivery in either reliable for or just best effort delivery. When we try to explain the word reliable, we refer toa loss recovery, which means that data transmitted arrives at the receiver side with no losses. We also refer toa the flu control the adjustment off the flu between the sender and receiver. According toe the natter conditions and according toe the requirements off the where. If there are also two data ordering, Sometimes data arrived at the receiver side out of order. Arrive Data number two before data number one. Data number one is late due toa taking a congested path over the network. That's why they're the number two arrived earlier I mean, the piece off the this piece of data number two needs to be reordered in a reassembly process to be put in the right place after data number one. One of the responsibilities off the transport layer is the data deed application. Sometimes data is son twice and received twice the same piece off data. So we need a form or an identify that says that this data is a duplicate. This data is another copy off a certain data that has been received. So we need a deed application process toe. Eliminate the extra copy once more you either son and receive in a reliable communication or in best effort, delivery. It's the two modes where the transport layer works. The functionalities off the transport layer are number one the segmentation. The segmentation means dividing data into small fragments called segments that can be transmitted over the network. Different networks have different maximum transmission unit there for different MTU. The MTU defines the maximum size off one data piece carried through the network. This is the definition off. The MQ data is being divided and transmitted to the recipient via the transport layer. The MTU size is agreed upon between the sender and the receiver while establishing the connection and during the routine discovery. The MTU size is one of the parameters off the network that must be agreed upon between the sender, the receiver and the communication devices. The second functionality off the transport layer is the reassembly. Reassembly means assembling the pieces off data arriving at the receiver side, so the same form or the same initial form that has been send from the center. This reassembly is done at the receiving end. The transport layer protocols reconstruct data into its initial for data can be received in different order, different than the form that has been sending it. So it is the responsibility off the transport rail to rearrange those pieces of data into the correct order. The original order, the order by which it has Bean sent the third function, like of the transport layer, is sequencing using the sequencing identify roar sequencing number to avoid the loss on divided application. Each piece of data is noted by sequence number or sequence identified. This sequencing fixes the issue off following data. Different path is so, you know, from the sequencing identified the correct sequence of data. This sequencing helps in organizing data in groups, off subdivided data signals and in identifying the order of groups off data sending and interpretation. The communication in the transport layer is either connection oriented. This type of communication that is called connection oriented is reliable and more secure. It is based upon establishing two way connection between the notes. I mean the sending and the receiving notes before data transmission. For example, when a browser is trying toe open a webpage, the transport layer would send synchronization packet, toe the Web server from the browser. The browser. Then expect synchronization. Acknowledgement response. When it receives this response from the server, it sends its own response to the server back. After this process is done, the data can be transmitted. We can hear See that no data has been transmitted before the connection establishment is complete, the transport layer can establish a connection in another mood that is called connection less oriented. This is a nun reliable connection. This connection depends on the best effort delivery between the sender and the receiver. No connection establishment prior to data transmission. It is less insecurity because it does not guarantee that loss, recovery or the re ordering off later if received out of order. It allows sometimes for data flooding for sending big chunks off data over the network, causing it to flood to be saturated with unwanted traffic. But this type off connection, less oriented communication is essential in some types of communication where data is really time data is delay sensitive, such as the audio data in the audio calls or the video data in the video streaming sessions . Now let's move toe the third layer layer number three, the network clear. Remember that we count layers from down to up. This layer organizes data into packets. Now remember that data in the fourth layer is schooled segment. And here, if it's cool, packets responsible this layer off end to end addressing and routing. And let's no by heart, these two words addressing and routing These are the main functions off the network. Clear. The network clear identifies unique logical address for each machine over the network. The address is unique. The address cannot be repeated. The address is logical and related to the geographical location off the machine. It is not a physical address. It's something logical that can be changing according to the change of the geographical location off the machine. This not declare Select the best path for destination. This what we call the routing process routers. The devices that are called routers work in this network. Layer reads and understands data upto this third layer layer three they're not were clear. This layer performs fragmentation. If segmentation was not enough to divide the data to be suitable for sending and receiving , we add another process that is, fragmentation. Toe the data to divide data into smaller chunks not clear at the receiver. Side receives the segments off data from the transport layer. Converts then converts segments into packets by adding the addressing information. The source is the destination and then finds route for later to be delivered to the receiver. Routes that are designed to any a group of data may differ because it is being the determined based on the following. It is either the least network overload the drought over the best route from the point off view off the quality of service, or it is the least drought in Khost or according to some delivery priorities, which means that the data has a priority more than other data, so it should take a path that is faster than other data would take. These are the most common criteria for route definition. When we say that the network layer is responsible for identifying logical address, we must give some details about the logical address. It's a unique identifying it is bound to geographical location off the machine. It is used for end toe and routing. Since bound to the geographic location, it can be changed it according to the change of the bigger geographical location off the machine. It is not vendor oriented, as we will see in the next lectures there. The physical address is vendor oriented. The common example for this type of address is the I. P address in the TCP I P Protocol suit. Let's sum up most layers. The network and transport layer the network clear. Our identifies the source machine and the destination machine in any session, while the transport layer guarantees either and toe and reliable delivery or end toe and best ever delivery for data across the same machines. These are the main functions off the network and transport layers in the ISA west. Sorry, seven layers. Thank you 9. Data Link and Physical Layers: Now let's talk about the lowest two layers. The data link layer, layer number toe and the physical layer layer number one. They are important layers, as well as the third and the fourth. For the network specialists and engineers, the data link layer Layer number two. It's a reliable layer for the data transfer across the physical link. It is responsible for their alien reliability on the level off hop toe hope. Transfer across the physical link means that it is responsible for the reliability off data transfer from the machine toe the switch and from the switch so the router and from the router toe the next rotor across the land domain, it is responsible off physical. Addressing. Physical addressing is different than logical. Addressing the physical address is not bound to geographical location and cannot be change it. The logical address is bound to the geographical location and can be changed according to the geographical location, off the machine or off the network interface card inside this machine. But remember that both addresses are unique and cannot be repeated. The data link layer organized the data into frames. The frame is the data unit at this layer at the data link layer at layer two week old data frames at layer, three week old data packets and at Layer four, we call data segments and that their one we will call data bits or bytes. The data link layer puts the frames on toe. The physical media checks four frames errors, and this checking does not include correction. It is just other detection only it is responsible for hope. Toe help addressing, addressing on the range off land domain at dressing with the physical address. The physical address is a unique identifier that cannot be repeated. It is not logical. It is not bound to the geographical location. It is only used for help toe hope. Addressing toe. Identify the machine on the land. I mean the physical addresses burned on the network interface court and it cannot be changed. It is vendor oriented. Every specific board off the physical address comes that this network interface card belongs to this vendor, which means network interface card from a certain vendor should have a physical address that is related to this vendor. A very common example of the physical addresses. The Mac address the medium control, the medium excess control address. Sometimes the physical address is called the hardware Address. The data link clear receives data packages from the network clear when sending and convert this data into frames, including the following the data itself. The data package, the sender and the receiver, physical addresses, error checking and control information. A field that helps for error. Checking for this frame checking and control ensures the frame has been delivered without troubles. This is the functionality off such field for error, checking and control. If part of the frame is lost during transmission than the data link layer protocols off the receiver would see that they telling clear at the receiver, Request data retransmit from the sunder. As you can see, this is just a re transmission request, not a correction action that can correct the data. Ah, that is corrupted at the frame. It is just a re transmission for the corrupted frame or for the frame that contains wrong information. The switches and the bridges are devices that work in the data link layer. Work in both layers, physical and datalink. Switch and bridge work in layer to the frame check sequence. FCS is the error checking mechanism that is created at the data link layer. The FCS is a number based on the values off all the preceding fields in the frame. The receiver receives data with the F. C s value. The receiver compares the FCS toe, the data field in the frame to check if this FCS is consistent with the data or not. If in an unlucky scenario off failed comparison, the following is done. If this FCS is saying that the data is not consistent with the field off FCS, the data is assumed to be corrupted. Then the receiver requests data. Resending from the sunder. The FCS is also beneficial. If the comparison is successful, the receiver sends a message off successful data transmission back to the sender. If the receiver did not receive the success message during specific specific period of time automatically. The Sunday reasons the data frames the data link layer is divided into two sub layers. The LLC, which is the logical link on throw layer and the make clear the medium excess controlled layer. Another function of detailing clear is it control the flow when many different nodes are sending data. At the same time, this is the layer where collision is detected and avoided. This is the layer where the schism a CD and this is Miss C. A. If you remember, collision carrier sense, multiple exits, collusion direction or carrier sense multiple access collision avoidance take place and are implemented. The day telling Claire has been divided into two sub layers by the I Tripoli, which are the logical in control, the lnc and the medium excess control. The LLC is responsible for the hope Toe hop, reliability and Hope toe help flow control. Reliability means that the data must reach each of the station with no others, and the flow control is the synchronization between the speeds off the sender and the speed off the receiver. The Mac layer adds the physical addresses to the frames off the sender and off the receiver . It is responsible off communication with the physical layer. Let's talk about the physical layer. The physical air transmits bit streams over the physical league data at the physical airai . Other are either bits or bytes. It stands data signals to media and receives it. That physical connection that really exists among the seven layers is between the two physical layers off the sender end off the receiver. Other links that exist between the data link here and there are just logical links. The physical layer adapts to the transmission media. Either these cables or wireless media. Either it is copper or fibre optic. Either Tisco, excel or twisted pair of copper or single mode or multi moody fiber optic. It is responsible for the representation off the ones and zeros responsible for the digital representation. Is it plus five volt Oprah or Plast revolt or plus zero volt? The voltage and the electrical representation is the responsibility of the physical layer. Devices that work in the physical layer are the nick the network interface scored. They help the repeater. All of these are devices that work in the physical layer only as we can see here are two stacks off seven layers for the thunder and for the receiver. We can imagine a logical link between the application layer here and the application layer there about the physical link that really exists. And that is not imaginary. Inside. This diagram is really between the physical link at this underside and the physical link at the receiver side. It is either through optical fibre or copper wire or electromagnetic waves in the wireless media that transmits a stream off bits and bytes from the physical year here, toe the physical layer there to represent the data off zeros and ones being sent from the sunder toe the receiver. By this we come to the end off the datalink clear and physical layer Explanation. Thank you. 10. ISO/OSI Model in Action: Now let's summarize the eyes. Always. I model in action and have some review questions for Section one and Section two off this course, the eyes was I Model is a conceptual model. It's a group of concepts that characterizes and standardizes. The communication functions off a telecommunications or computing system. The eyes OS I model is just concepts. You can bend upon these concepts any hardware or software system that can communicate with each other. This conceptual model is regardless off underlying internal structure and technology. The goal of this model is to provide interoperability off divers communication systems with the standard protocols, which means win the systems can communicate with Linux systems. Any vendor can manufacture or implement a hardware or software system that communicate with another hardware or software system implemented by another vendor. Since they are using the same protocol, this is the only condition or criteria that they must use the same communication protocol. The eyes voice I model partitions, a communication system into abstraction layers. The functionality of each layer is contained into itself. The functionality of each layer is done through interoperability with the upper layer and the lower layer as well. The original version off the model, they find seven layers. It's very important to know these layers application, presentation session, transport network, datalink and physical layers. Each layer serves the layer above, and it is served by the layer below it, or vice versa. Each layer can be served by the above. Answer the lower layer. It depends whether you are sending or receiving data when sending data. The data is going downwards when receiving data later is going upwards through the several layers. Remember always that layer one is at the bottom and later seven is at the top. A layer that provides other free communications across the network provides the path needed by applications above it. This is an example this layer calls the next layer, which means the lower layer to it. After providing the puff to send and receive packets that compromise the contents off that path from where did get didn't get that off from the above layer. So this lower layer got the path from the above layer, and then it does the functionality off. Sending two instance at the same layer are visualized as connected by horizontal connection in that layer. Remember that the only physical connection is between the two physical layers only, and there is a logical layer that is between the application layer here and the application layer there. The application. We're here at the sending side at the application layer there at the receiving side, there is a logical connection also between the presentation and the presentation, the session and the session, the network, the network, the datalink and each of the seven layers is connected virtually but one off them is connected physically, which is the physical year here and the physical layer there. Let's have a look at this diagram. This is an important Bagram. Let's look at sending at the left side the layer 77 Sons data. This data is added toe the heather at six Atler six. Now see that both at seven and six, considered as L six data where at the layer five h five is added and now see the same thing happens one time again. And six plus H five are both considered as l five data where at the transport layer, Etch four is added at six h five h four are all headers added by layer six layer five and layer four. Consequently, both L five and H four are considered as L four data, where at three is added now the only layer that adds heather and trailer trailer, which means that is something before the data. And heather. There's something after the reader. The only there that adds heather and trailer is the data link layer, and the physical layer considers all the data as zeros and ones. Then it is passed through the transmission medium. You can see at the right side that the reverse thing is happening. It's vice versa. It's the reverse action off things that happened at the left layer. You can see that each layer added each heather or trailer added by a layer at the left side is red and removed by the same layer by the corresponding layer every at the right side. So each toe Tito already and removed by the data link layer and receiving sight. Touch three is red and removed by that not clear at the receiving side. So at the receiving side at Layer seven off the receiving side, you can only see L seven data that was originally sent by the application layer at the sending side. That's why we we say that there is a logical communication between the application at the Sunday inside at the application at the receiving side, because they are sending the same data and receiving the same data that has Bean sent. Let's summarize and say that the open system interconnection, the always I model defines a network and at working framework to implement protocols in the seven layers. Now let's have some review questions about Section one and Section two. The first question says the computer network is composed off computers dots, and that's connected through transmission media. What are the other components off computer network peripherals? Remember preference. Any hardware piece that can be connected to a computer connecting devices? This is the other component of a computer network. So the complete sentence would be the computer network is composed off computers, the reference and connecting devices connected through transmission media. The second question Transmission media can either be made off or or it can be using that as a transmission. Media transmission media can either be wired, made off copper or fiber optic as materials, or it can be wireless, using the air as a transmission medium or as a media off transmission. This would be the complete sentence. The most commonly used network topology nowadays is there star topology, where the computers are connected to a central device which is there. Switch off course. It can be a hub, but we are talking here about the most commonly used, and here I've chosen it to be the switch toe let you give familiar with the most commonly used device. Based on the cover of geographical area, the network can either be a or A. It can either be a Len or a went off course, while according to the transmission type, it can either be peer to peer or client server network. Now let's move toe section toe the most commonly used types of copper cables. Is there twisted pair, which is divided into STP, which means she'll that Mr Pair and You tp, which means unshielded twisted pair cables according to the type of shielding the advantages of fibre optic cables over copper cables, are that it is festive and can afford higher capacity and more immune to E. M. I electromagnetic interferes and more secure than the copper cables off course. Since it is not susceptible to sniffing the term OS. I stands for open system interconnection. The most commonly used protocol over the Internet. Is there TCP I people to gold? Among the protocols that work in the application layer are there http ftp de on us, SMTP and others Of course, the transport layer can work in either or modes off delivery in either reliable or best effort Moods off delivery The main functionalities off the network layer out of there addressing and routing functionalities. And of course, the routing is based on the addressing off course. The type of addressing at the network clear. Is there logical addressing the network layer is responsible off. What about addressing that? He is a question, of course. Logical addressing while the datalink clear is responsible off. What type of addressing physical addressing. Thank you. 11. Introduction to Computer Networks Protocols: Welcome toe, the third section off our course. It's about the computer network protocols and the meaning off the world protocol in the world. Off computer networks. What is a protocol in the world of computer networks? It's a set of rules and agreements that governs the communication process. The process off sending and receiving It includes this rules and agreements the addressing , the routing, the session management and the editor recovery processes if needed. How to address the machines, how toe route messages between the machines, how to start and stop any session between any two machines. How to recover the loss or that application off any data between two machines. The male Network The Post Network. The Courier Network, The traditional Maryland Mail Network, is an example of a network with a protocol. Imagine that you need to send and, ah, a maid, a certain mail that is written on a paper and included inside an envelope. You should write on the face off the employees that the address off the man you are going to send the mail, too, and you will also have to write on the back of the envelope. Their address of yourself this is a protocol, a protocol that dictates on you some rules and agreements on how to ride the address, where to ride the address and on which piece would you write the address, which, which is the envelope here? The envelope here includes the headers off the data and the message itself, written in a paper inside the envelope is that data itself that needs to be sent between the sender and the receiver. The PSD M, the public switched telephone network, is another network that is running through a protocol. Every telephone has a unique number that is, ah, worldwide, not repeated, and that is worldwide connected to the geographical location. Off this telephone, the mobile phone network is a network that has also a protocol. Each mobile phone number is unique. Each mobile phone number has a route toe, another mobile phone number in the world. Each mobile phone number can start a session and this session stop and resume a session with any mobile phone. Not all over the world. The layered model that appeared with the eyes OS I model has so many benefits in this subject because this layered model allowed off separation off functions between the layers off the protocols so a layer can be responsible off addressing another layer can be responsible off the recovery. Another layer can be responsible off the session management. This is the session layer. This is the transport layer. This is the network layer. Another layer is responsible for the network access, which is called the Datalink Lair. Every layer in the several layers has its own responsibility and is served by the upper and the lower layers to it toe Act as a sender and receiver for data according toe. The process being done. The most well known computer network protocols that appeared over history was the net very high. PX SPX, Apple Talk and the well known and very famous. A standard protocol TCP I p. The TCP I P is the standard protocol over Internet. TCP I P stands for transmission control protocol. Internet Protocol. It's compatible with the eyes. Always I model. It provides interoperability between different hardware and software systems, since it is standard. Since it is compatible with the eyes OS I model, it can be implemented by any off the hardware or software manufacturers over the world. It's open for development it is not owned by a certain vendors, so it is open for development by researchers over the world. It provides reliability. It provides some sort off connection orientation. It provides some sort of a recovery and reliability in data transfer as well as best ever delivery. If this is the future that is needed. And sometimes we need the best effort delivery feature when we are caring about the speed more than the reliability off the communication. This is very obvious in the real time data in the audio and video data, it is composed of a number of protocols. That's why we call it the TCP I people to call suit. It is composed of a number of protocols in the application layer in the transport layer in the network clear that are built over each other to form the TCP I people to call suit. It offers Web browsing, file transfer and email exchange. This means that it offers the most famous and the most demanded and the most wanted services over the Internet. T. C P I. P has produced version four and has produced version six, and both are running. Version four is more common version six is the next version and it is the current version in some countries over the world for communication over the Internet. This is the TCP I people took old suit. Let's have a look. Let's have a look at the upper layer that that is composed off. Http. Ftp telnet, SMTP the n stf DPR PCs and empty These are all protocols in the application layer in layers . Seven. Off the eyes, OS I or let's say that it is in layer seven and six and five in the eyes. OS I model and it is in the upper layer in the TCP I p. The transport layer which is the layer four in the eyes. Always I modern includes here anticipate a I p two protocols. One of them is reliable. That is, the TC people to call the other. The other is unreliable, which is the UDP Protocol that will clear the third layer in the eyes. Os I model is translated here in tow one layer that is called also the network clear, including the I P Protocol. As the main protocol and other protocols such as the ICMP the are there are Andrea, the dynamic routing protocols here. These this layer is responsible for addressing and routing the lower tour. There's the datalink and the physical air includes some off the protocols responsible for accessing the network for data representation and the functionality off the physical. And they telling clear, such as the Ethernet token ring the FBI. The A T M a. T M here means a synchronous transfer mood and eyes the end. Other protocols that are responsible off transferring data representing one's and zero's. Accessing the media, a violent collisions and such functionalities off the day telling and physical air off the eyes. Always I model Let's here have a look more in depth about the mapping between the TCP i P and the eyes Os I model the TCP I p iss seven layers. We all know this, but the recipe I p model is only four layers. You can see that the upper fillers has bean murdered together to form the application layer in the TCP I. P. The transport is still the transport. The network has been translated as it is with the name Internet and sometimes called the transport as well that lower two layers are they telling and physical and are called the network access layer in this D c P i p. So let's say this again. This mapping between the eyes O S I and the TCP I p has done through merging off some layers. Toby four in the TCP I p model instead off seven in the eyes Os I modern. This has done through merging the physical and they telling keeping both the network and transport layer merging the upper three layers in tow. One layer called the application layer the TCP I P is now that the fold protocol that is implemented inside any Microsoft, Linux or any other operating system that needs to be standard that needs to connect machines over the Internet, TCP I. P. Is now Standard is now built in inside Microsoft operating systems. Lennox operating systems and other operating systems that are produced on machines needs to connect over Internet. Let's now have a look at the mapping between TCP I p. The eyes always I three layers has become one layer application. Presentation Session has become the application and example protocols that are learning in the application layer off the TCP I P R the http telnet. Ftp smtp Deanna's r i p Which means routing information protocol as an API, which is simple Network management protocol Indian as the domain name system or server. SMTP Simple mail transfer protocols, FTP file transfer protocol and tell that is used for remote administration. The transport layer is mapped in the TCP I paean to host to host transport layer. This is mapped in tow, either TCP in the reliable communications or UDP. In the unreliable communications, the network layer is mapped through the Internet layer. The I P layer is the main layer that is the main protocol, or the main layer working in the network layer upper to it. We can find ICMP Internet Control Messaging Protocol, or GMP, Internet Group Management Protocol and the AARP, which is the address resolution protocol, which is responsible between the resolution between the two types of addresses. The Mac address, the I P address, the physical address and a logical address. As we will see later. The datalink and physical layers are mapped here in tow, one layer that is called network interface layers and is implemented in several protocols in the TCP I P, such as the Internet, which is the most commonly used over today's networks. The token ring, the frame relay networks and the A T M. This is the core off the TCP I p. This is the main mapping between the eyes OS I model and the TCP I P Protocol. Thank you. 12. IP Protocol: Now it's time to talk about the I key protocol. The network Clear Protocol in the TCP I P Protocol suit. The I P Protocol is the principal communication protocol in the TCP I P Protocol suit. It's the protocol responsible for the two functionalities off the network. Clear the addressing and routing. It defines the addressing to label the data graham or the packet with source and destination addresses, source and destination Logical addresses that are called the I P addresses. It relays the data grams or packets across the network boundaries from the source to the destination, depending on the route which is established according to the source and the destination I p addresses. This routing function enables inter networking and essentially establishes the Internet without routing. It's hard to imagine that there is Internet here. This routing delivers packets solely based on the I P address in the packet headed solely based on the source and destination I P addresses that are added at the network clear in the form of heather Toe the data in this layer, the I people took old structures packets and encapsulates the data with the source and destination I P addresses Toby routed and delivered over the network. What is the I P address? The I P addresses the logical address that is depend being on the geographical location off the machine. It's unique. It cannot be repeated over the Internet. Each single machine over the Internet should have only one I p address that is unique. It's logical and not physical, which means that it can be change it according to the geographical location of the machine . The length of the I P addresses 32 bits or four bites or oct. Its if you can call it like this. It's ah, version four off the I P address that is 32 bits. Version six of the I P address is 128 bits each bite or each Oct. It ranges from 0 to 255. This means that each bite is representing eight bits, and each bite can take the number from 0 to 255. The I P addresses are categorized into classes. We can see Class A or Class B or classy or Class D or close E I P address each. I P address identifies single machine and each i p address if added as a destination toe, a packet is used for routing from the source off the packet toe, the destination by the routers. It is red and interpreted by the routers, which read Layer three. Information the classes off the I P address and let's focus on the main three. Closest A, B and C has the rangers, according toe the number in the first bite. The first doctor. If the number of the first bite ranges from 1 to 1 26 then it is close. A. If you train just from 1 28 1 91 then it is close. B. If it ranges from 1 92 to 2 23 then it is close. C i. P. Address. According to this classification, there are possible numbers off hosts for each class. Class A supports up to 16,000,777 thousands and 214 machines. Each close B category can support to 65,534 machines each Class C can take 254 machines. Only the public I P addresses that can be given to machines to exist over the Internet in close A. It can be from 1.0 to 9.2555 and 2.255 point 255 It is red like this 1.0 dot 0.0 toe, $9.255.255 dollars 255. Then we skip the number 10 and move to the number 11. So the number 1 26 no tear that from Class A to Class B. We have skipped the number 1 27 and Ray close be ranges from 1 28 1 72 and range inside 1 72 It's also have some numbers skipped. You cannot see 1 72.16 for example, 1 72 not 15 than 1 70 to about 32. Still 191 about 255 Then we start from 192.0 dot 00 to 192.167 Then we skipped 192.168 and start again from 192.169 toe to 23 about 2 55 to $55 to 55 here ends the close. See where Starting from 2 24 starts. The close, the and close Theis for the multi casting address addressing the private I P addresses that cannot exist over the Internet as Riel I p addresses as public I p addresses and can exist only inside local area networks. Are these ranges in close? A. Every I P address, starting from starting with the number 10 in close beep. It's every I P address having from 1 70 to about 16 till 1 72 not 31 in classy. It's any I p address, starting with 1 92.168 toe, 1 92.16 eight not to 55 any I P address, starting with 1 92.168 These are the Rangers off Private I P addresses that can be given to machines inside Ln and then connected to the Internet through some technology that is called the network address translation or netting to give many machines. Having such I p addresses such private I P addresses one rial i p address Toby contacted through over the Internet. This is to save the i p version for addresses that has become scarce resource over the Internet and allow for more security during the communication with the machines. Having private I P addresses over the Internet, there are some reserved I P addresses you can note now that the I P address is divided into two ports. The Left Port defines the network. The right part defines the host. So if the network address is a specific number and all the host address is zeroes, then this is the network address itself. And this I P address cannot be given to a single machine. It defines the network itself. It's an entry inside the routing table that we are going to talk about lately. The broad cost addresses is composed off network address that is specific, and the host is composed off all ones. This is used for broadcasting and cannot be also given toe a specific machine. It is reserved for broadcasting, So if we see an I P address that has the network address with a specific number and all the host address zeros, then it is an utter caters. Or if all the host address is once, then it is a broadcast address and cannot be given to a single machine. Devices working on their three devices Working on the I player are the router and layer three. Switch the rotor Endler threes, which are the devices that three directs packets between networks. The foreword packets based on the destination I P address and according Toe the routing table stored inside the router or layer three switch According to this routing table, the packet is investigated and is searching for the path that it should take based on its destination. I p. Address the outer looks at the Destination I P address searches the routing table for the right path, then forwards the packet According toe this path found in the routing table. Let's have a rule here. The network I d equals the I. P address ended with the sub net mosque. If we have a given I p address and given some Net mosque, The Summit mosque is something that mosques the I p toe get the network i d. If we end them together. This is a logical operation that is done between one sends ears and cold ending. If we end them together, we can get the network I d. Off this I p address Routers are protocol dependent. They did. They depend on layer three protocol. They're freeze, which differs from a router that it is super force than the router. It is completely hardware and uses hardware in routing mean one. Routers can use software such as the routing tables to be used in the routing process. What is the routing table? It's a table that is stored inside the router or layer freeze, which, if inside the router, than it is software. If it is inside the layer three switch the say that it is. It can be stored in a hardware four or a firmware. It is composed of Rose that are read sequentially. Each row is composed off several columns. A column. The four Destination at work, a column for Subject Mosque, a column for the interface that is connected to the router and that is used for forwarding the packet. A column for the Gateway. The gateway is the next router. It is the next hop for the packet to go through a column for the coast or the metric off the party, and it is used if there is a certain path that is an alternative. Both toe the main path off this packet so they are compared to each other in the point of view, off coast or metric. And the less coast, the less metric is chosen for this packet. The routing table can be bill ecstatically through the network administrators, which store this routing table inside the router or can be built dynamically through some dynamic routing protocols, such as the R. I P Routing Information Protocol or the O SPF Open. Short the staff First dynamic routing protocol. The destination network can be dedicated who are deducted from that destination i p address through ending with the sub Net Mosque. According to this, we can know the interface that the router is going to choose for forwarding the packet and the gateway. That will be the next hope for such packet toe goto. If we want to see a routing in action, we can look at this diagram. We can see the host source and registration host separated by three networks and two routers. Each source connect to its specific routed through indirect delivery. Then the router connects to the next router through indirect delivery and Then the last router connects through the hosts Through direct delivery. We can see that each two machines connected through the same, not accuses. Direct delivery routers contact each other through indirect delivery because they are not connected directly through the same network. This is routing in action. We can imagine that this host machine is in a country. And this distillation machine is another in other country where an ocean can separate them . But packets can go through these routers from the host to the destination according to the routing table. According to the path chosen by the routers Toby delivered from the source to the destination based on the destination I P address. Thank you. 13. TCP and UDP Protocols: Now we will talk about the two main transport layer protocols in the TCP I P Protocol, the TCP Transmission Control Protocol and UDP User data Graham Protocol. The transport layer in the eyes OS I model off course is layer for and in the TCP I P implementation. It is implemented in two protocols. The TCP and UDP. You either use this or use that you use the TCP for reliable communication if needed. Or do you use the UDP for unreliable communication? If this is the needed mode that transport layer is responsible off session multiplexing multiplexing means that several inputs leads only to one outward. This is the responsibility off the transport layer to let every service at the source talk specifically toe the corresponding service at the destination site. It's responsible off flow control if needed. It's responsible off adjusting the flu off the data, according toe, the slowest side, either the sender or the receiver. It lets the faster side slows down. Toby suitable for the slower side. It's responsible for reliability if needed for lost detection, for our recovery and to end. It's responsible for dividing data into segments, adding the port number and the port number is a very important identified toe. Identify the type of service requested from the client to the server or from the source to the destination. It is responsible for the communication socket. So socket and let's see what is a socket. The socket is a combination, as we can see in the diagram is a combination between the I. P address that we have talked about and the fourth number that we need to talk about. Now. What is a port number? It's the island. The fire for the service. Each port number is associated with a certain service over the Internet, especially the port numbers ranging from 0 to 1024. The lands off the sport number is 16 bits. That's why we can say that the port number can range from 0 to 65,535. Among these port numbers, the port numbers, ranging from 0 to 1 24 are the well known ports. For example, port number eighties. For the http port number 21 is for FTP 53 for the Ennis 25 4 SMTP. Simple mail transfer protocols. Port numbers larger than 1024 is called a fair Merrill Ports Ephemeral ports means that they are not the well known ports, not associate ID toe very well known services, but can be used for the communication from the client side to the server side. While the West known ports are dedicated on the server side. For each of the services such as http ftp, DNS or SMTP, here is the socket communication. Here we can see the socket Address I P address and port number forming a socket address. This socket address is at the source and a corresponding one is formed at the destination from the I P address off the distillation and the port number at the destination. Here is a socket at the source, another one at the destination. They are communicating with each other in socket, so socket communication. This is the responsibility off the transport layer layer for the responsibility off the TCP Protocol or the UDP Protocol. Let's compare between the reliable communication and the best effort communication there. A lot of communication is connection oriented. No data transfer before connection establishment, but in the best effort communication, it is connection. Less data can be transmitted without establishing a complete connection or a complete session complete circuit from the source to the destination. The protocol used for reliable communication is the TCP. The protocol used the four. The best effort delivery is the UDP Protocol there. A lot of communication provides a means off sequencing the sequence number in the TC people to cool in the best effort. The Love Delivery. You cannot specify the sequence off the data, which is before which or which is, after which the uses off the reliable protocol are for transferring email file sharing, downloading files. The best effort delivery is for transferring voice or video. In general, it is four really time data. It's for later that is delay sensitive and not lost sensitive, such as the voices screaming or the video streaming Where UDP is much more efficient than TCP, the U. The people took over as the first protocol in the transport layer. It's disused in the best effort delivery. It is unreliable, but it provides application with access to the network layer. It saves the overhead of reliability mechanisms it saves. The acknowledgement saves the sequencing off later, each off the acknowledgement and sequencing needs. Adding Heathers and they use the people to call, saves this heather and saves bend with for the data itself, the voice or the video being transmitted its connection. Less protocol. No connection establishment Before sending data, you send data and you are not sure that the recipient is there. The recipient is up and running. The recipient will receive the data in sequence. It has a very limited error checking, and this checking does not include recovery off errors. If existing it is they're not resilient. Toe day. Tell us, and they will also scan beat you toe routing errors or the application. The GDP protocol provides no data recovery features for such losses, so it is completely unreliable and therefore it is used with the delay sensitive data and not for the lost sensitive data. The UDP heather. It's simple and it does not provide any form off better recovery. So it is simply composed off that source sport registration. Poor David appeal ends and they will be check some their checks on the header only it does not provide error. Recovery does not provide acknowledgement sequence number, as we will see later in the TCP Protocol. The TC people took over is the reliable protocol. It's the reliable version off the protocols that are acting on the transport layer. It provides access to the network layer for applications just like the UDP. But it is different, different in the way that it is connection oriented protocol. Before data transmission, there should be an establishment off connection complete circuit between the source and the destination. It provides error checking. It provides data recovery features and to end if there is data lost data application or any change in the data from the source to the destination. The TC people took hold can detect this can detect the loss and the application in the later and can recover this by resending the data itself. It provides sequencing off data through the sequence number Heather that existing in the header of the TCP. So if the arriving data is in the wrong order, the sequence number helps the receiver to reorder the data toe the right order. It provides acknowledgement of receipt, so by this it can face the losses on the network and can detect that some data are lost and can be re sent by the source. The TCP Protocol for the sake of such features. The features of data recovery, sequencing and acknowledgement is more commonly used than UDP because it is reliable because it is more, ah, error resilient. So it is more commonly used than UDP, especially for Web transfer, male transfer and file transfer. The TCP header is off course more complex than they really p heather. We can see the source for the registration port. We can see the sequence number used for sequencing data. We can use the 32 bit acknowledgement number, which is used for acknowledging data being something we can see the 16 between the size used for flow control. We can see the check some, which is the strikes, um, anywhere used for checking errors across the heather and the data. We can see the 16 bit urgent pointer, which points on that urgent data inside the data field. If this field, for example, contains the number 2000 this means that the by 2000 in the data field is urgent and needs to be processed before its turn comes. So this is the TCP heather. We have some flags for the urgent feel, for example, for the acknowledgement for the push for the same for the fin that are used for the three way handshaking used at the beginning off the session off TCP communication and the four way handshaking used at the end off their session off TCP communication. If we try to map layer four protocols to applications layer for protocols and the port number toe the application protocols, we can see that the FTP protocol use a sport number 21 uses the TCP as the transport layer Communication protocol. Tell not uses 23 esport number tell it is used for remote administration. It is used by a client toe administrate a server remotely and act as if sitting on it, copying and pasting and formatting the machine from another remote machine. And this is done through the port. Number 23 the http the hypertext transfer protocol use a sport number 80 and it uses the TCP Protocol so it is reliable so it can correct some errors. It is resilient to data losses that he on us is a special case. It can use the TCP and can use the UDP. In both cases, it uses the port number 53 it can act in a reliable form using the TCP Protocol, it can act as unreliable form using the UDP Protocol. If speed is more important than reliability, the T FTP or the Trivial File Transfer Protocol use a sport number 69. It is just fund transfer without any user name or password or something like this. It is faster file transfer than the normal FTP. That's an MP or the Simple Network Management Protocol, which is used for managing the network. It's used for communication between the routers. It is a protocol that is used to manage the network and make it faster and more robust. It uses there would be people to call for the sake off the speed and the Sekoff being fester. And it works on the port number 161. By this we come toe the clear demonstration off both the TCP and they were the people to calls, acting in the transport layer off the is OS I model and the transport layer off the TCP I people to call as well thank you 14. Application Protocols: Now let's talk about the application protocols. The protocols that work in the session presentation and application layers off the Aiso, a sigh model and in the application layer off the TCP I p Protocol. These protocols are such as the http or http s that offers the web services. The https is the secure version off. Http. This US is for security or, like the file sharing services FTP or T ftp file transfer protocol or Trivial file Transfer protocol or the mail services. Simple mail transfer protocol. SMTP pop three or I met Post Office Protocol version three or Internet message Access protocol or the DNS services. The Domain name System services. These are the protocols or example protocols that work in the application layer off the TCP i p each of them. It has a dedicated port number. Each of them offers a certain service between the source and the destination between the client and the server over the Internet toe. Offer a certain service to the user off such protocols. Let's start by the http http stands for hypertext transfer protocol. It supports the Web services. It supports the transmission off images, texts and hyperlinks between the Web server and the weapon through the Web browser. It supports the older www patriots that can be transferred between the server and the client. It uses port number 80. The secure version off http is actually TP as us here is for security and https uses the port number for four 3 440 three actually pp is one off the application layer protocols in T C P I, p FTP or the file transfer protocol. Use a sport number 21. It has a built in application in the M S Windows operating systems. Microsoft Windows operating systems. Many third party programmes can act as FTP server and client as well to transfer files between the FTP server toe the FTP client. The Web browser anywhere browser can work as an FTP Klein. If you replace the http saw fix at the start off the U R L way, the word ftp, then it will work as FTP client and can be able to transfer files The email protocols we can see in the diagram that the email client is contacting the email server through two protocols. One of them is for sending, which is the SMTP and the other is for receiving emails or downloading email messages from the email server to the email plant, which is the pop three. The communication between mail server, EXE and mail server. Why is done via See the SMTP Protocol Simple mail transfer protocol. The SMTP is the common language between the majority of the mail servers around the Internet. Once more at the client. Why the SMTP is used for sending emails from the client to the server client y two server. Why and the pop three is used to download messages off client. Why from the server Why the pop three or the I met? It depends whether you want to download the message through pop three or toe just excess. The message through the I met the SMTP is the common language used by the majority off the mail servers. As we have said, it sends messages back and forth toe other mail servers and it is used to sending message between the mail client and to the mail server. The Post Office protocol is for receiving and collecting email messages from the mail server to the client. It downloads the messages on the machine so the user can work off line, can now load the message at the beginning of the session and then if the Internet cuts, it can work off line. This saves quota on the server, since the messages are downloaded from the server to the client, so the coat off the user can be emptied for other messages to arrive. Internet. No such access protocol is another message. Toe access the messages by the Clement on the server. It is just for accessing the messages, reading them. It does not download the message. It does not save the court. Eight. Retrieves only the message header allows the user to read the message about the body of the message. The message itself. It's at the server side, So this is more commonly used if you are accessing your email from a machine that is not yours from a machine that you do not want to download your messages on the Deanna's Protocol. One off the application protocols working in the TCP i. P. The understands for domain name system or domain name servers. In some written texts, the DNS resolves the domain name in tow. I p address. For example, www dot cisco dot com is the domain name. This is a name that can be understood by the human, but the machine needs numbers, needs addresses to work with. So this resolution between names that are understood by human into addresses that understood by machines is done via the DNS. The domain name system. The D on a server here matches the human address with the numeric address. The device used numbers understands only ones and zeros and numbers, so www dot cisco dot com is mapped into the address 1 98.1 $33 to $19 to 15 Humans can easily understand names. Machines can easily understand addresses and the N S acts as the resolution machine for resolving names in tow addresses. This is the DNS tree around the world. We can see that we have websites or domain names ending in dot or dot com dot de that I s that UK and not any thing we have each country in the world have two letters suffix like that UK United Kingdom bodies for Germany and we have dot org's for organizations come commercial video for educational Mel for military and not for networking organizations. And we also we have some organization names that are governing the Internet, like the i E T f Internet Injuring Task Force and the other organizations that can work and manage the Internet as examples off them domain names that can exist over the Internet we have here the www estimate she named that can be connected toe i e t f as that parent domain name, then not order. This forms there fully qualified. Domain name off www dot i e t f dot org's as a website. If we can see the on us in action here we have a DNS climbed that contacts. It's locally in a server asking for what is the i p off cisco dot com. This local Deanna server does not have the answers but can ask, apparently in us about things that ends in dot com. What is the i p off cisco dot com and the parent can answer it with the I P address off Cisco would come. Then the answer is transferred toe the DNS climb. Sometimes this local Deanna server cashes the the answer for the sake of not asking once more for that previously Oscar domain names and can answer about www dot cisco that come from its cash in the second time it is asking about from any other client than the first line. We have also a very well known and famous protocol working in the application layer that is called the D. H Sippy Dynamic Host Configuration Protocol. It's an important protocol in the configuration of the CCP I p parameters Inside any machine. If a client on a certain network boots and moves to be up on the network, it sounds a d x api Klan broad cost Discover message that is read by several servers over the network that he is connected toe several D HCP servers. One of the server sends the D fcv server broadcast off her message, which means that he offers the client some of the TCP I p parameters that he can take toe start and work over the Internet. What are these parameters? These parameters are the I P address, the subject Mosque that if we'll get way and the DNS mainly the yen a server that he can contact oh, communicate over the Internet, then the client responds with the request message for leasing and asking for these parameters. The offer message says that I'm server a media recipe server. I can offer you these parameters. Then the SCP server finalizes the exchange with acknowledgement. Message finalizes that this client has reserved this. I p address this some net mosque, this default gateway in this Deanna so that he cannot repeat leasing the same i p address to other machines. Otherwise, there will be a conflict of I P addresses between two machines and this is forbidden. No two machines can have the same i p address over the same network. So what is the main benefit off this? The HSP It saves the offers. The efforts off the network administrator that is used in configuring several machines with I p addresses subject mosque, the fold Get way. Deanna servers. It saves this effort and makes a machine. Does this task off course the machine does not make the mistake off. The I P conflict does not make the mistake off assigning the same I p address to two machines. The D A s a. P, as a protocol is very commonly Weide widely used over the networks don't least i p address to distribute I P addresses over several machines on the same network and to save the effort and received the mistakes that humans can do by conflicting i p addresses by this we have suit should some off the application protocols working on the application layer off the TCP I p protocol suit. Thank you. 15. TCP/IP Tools: Now let's practice. Let's recognize some off the TCP I p tools some of the TCP i p commence that helps in troubleshooting the network and in ah, determining the i p addresses off the machines and the domain names off the Web sites and so on. Let's start by this command, its I p conflict. Let's try this command. Now, how do we try this command? I p config And what could be it could be its output. I p config is used if we type it here on the command prompt. It is used to determine the i p address the physical address that Gateway address the Summit mosque and other addresses all the TCP i p configuration off the machine. If we type I peek on fig slash old we get more configuration in details about the TCP I p configuration off all the Ethernet guards and the WiFi cords existing on a certain machine laptop or ah, PC or any other machine that we need to know its i p address. It's gateway or its DNS that is resolving the meanings for it. Or it's gateway, the router that is connected to this machine toe connect it toe the Internet. The second command that we need to know about is the Ping Command. Ping Ping stands for packet Internet dropper. We can access the help of this command that manual of this command by typing King minus question more. Here is the help Here is the manual off this comment. For example, if I type now paying www, not Yahoo that come. I'm testing the connectivity between my machine and yahoo dot com. Either I get a reply, which means that I am connected where I get a request timed out, that which means that I'm not connected to such machine so I can typing, followed by an I p address and being followed by a domain name I can typing for a domain name, followed by the switch minus T, which means that I need toe execute and interrupted an uninterrupted ping being that goes on a number off packets and sends to me the reply until I press control, See to stop this operation here. I'm connected to google dot com and request the ICMP request. Packets sent by this command is replied by the ICMP replying that is appearing on the CME. The screen. I can specify the number of packets sent by my machine toe the distillation machine I need to pink, for example. I can typing minus and six www dot google not come, which means I need only toe send six packets and see the reply. Only here are two, 345 six and then it stops. Ping has so many switches. If I need to know all the switches off the ping command and need to know more about them, I can typing minus question, Mark, and go on and see these switches and its usage and try to use them one by one. The other command that I want you to know about is the argument ARB stance for address resolution protocol. And as we have said before, our is the resolution protocol resolving the logical address into physical address resolving the i P address in tow. Mac, address If I type r minus question Mark, I get the help or the manual off this command and can read the usage off this command, the most popular usage is using ar minus A to display the AARP cash off a certain machine here we can have the Internet address and the physical address corresponding to it that our store, the inside the AARP, cash off this machine and used for the resolution between the I. P and the physical address. This is a Mac address. This is an I P address. Both are used for the resolution between logical and physical, and both are stored in the our cash off this machine, our command once more, can be used by several switches. You can have a look at art minus question mark to know the usage is off such switches. You can make your machine act as an FTP client. If you type the command FTP, then you can type open, for example, ftp dot Microsoft not come and then waits for the connection between your client machine and FTP that Microsoft dot com It may ask you about user name and password. If you supply them in a correct way, then you log in in tow. The FDP that Microsoft dot com to do what Toe download files from this FTP server to your client machine toe. Get some files through the command, get and then type the file name and you can upload some files through the command put and then type the file names. And by this you can upload some files from your machine toe the server machine, and you can type ls Which means that you want to list their contents off the FTP server that you are connected toe to end this ftp section You just typed by and then end this FTP session. Another command that we need to know about is an ASL Look up and as look up is a very useful command in determining the i p address corresponding to a certain domain name. For example, if I type here www dot google don't come, I can get the I P addresses connecting corresponding toe google dot com and connecting them to my machine. If I can type any domain name, I can get the corresponding I p address and vice versa. If I can type an I p address, I can get the fully qualified domain name for this I P address toe exit from this command. I simply type exit. Another command that we need to know about is that state not state minus question. Mark shows the manual and the help of this command with many switches that can be used. That state is usedto display their current connections of any machine. For example, if I type Net ST minus and I can see the machines that I am connected toe currently through the I P address on my machine, the I p address off the foreign machine, the connection protocol and the status of this connection, I can also type that ST minus A to display the same connections in the form off I P address on my machine domain name off the connected machine and the status of the connection. That state is very useful in determining and in ah specifying the connections that are connected to my machine in a certain moment, off time after this, after this commands has been listed, we can go through them. Here is the ping minus T minus and minus R minus. W minus T for uninterrupted being Manus and for specifying certain that number off packets . My big man is our for the out count, and Piemonte is W for the time outs but spanked them out. Here is the output off an arms cache of a certain machine using the R minus a Command here is using the FTP command to connect to an FTP server. You can you use open a less seedy been get em get put by these commands can be tried on the FTP session and as look up to resolve the DNS into the that the domain name in tow i p address Using the DNS system out, this command is used to print the routing table for a certain machine route print, for example, This place, the routing table for any machine that I am connected to, displays the routing table off the machine that this command is typed on the routing table and its components has been previously explained. And this is a simple routing table that you can have a look on. This is the distillation network. This is the sub Net mosque, the gateway, the interface and the metric or the coast. Just review the section speaking about the routing table, and you can see these columns as the components off the routing table. Finally, we come to the estate once more nuts ST minus in a state Manus and and that ST minus P shows the connections with the name off the protocols that ST minus p, for example. And then spasticity shows the connections made through the TCP Protocol. Only through this machine where you type this comment. Thank you. 16. Wireless Networks Benefits: Welcome to the wireless sexual. Let's start by exploring the benefits of a wireless network over a wired network. The benefit of a wired network is mobility, flexibility scalability it. The wireless networks enables that you can bring your own device, the wireless network. Sometimes it's more cost effective than the wired one. When we say mobility, it is the biggest attraction towards going toe wireless because in most of the times we need to be mobile inside the place, and at the same time we need to access the network we need to be online. We have so many mobile devices nowadays, such as the laptops, mobile phones and the tablets. These devices can access the latter through the wireless connection. While you are moving, mobility enables access anywhere in the quarters, in the corridors in the meeting rooms. Any off these devices can access the network through wireless connection from the corners from the corridors from the meeting rooms and as well. You can have mobile voice over I P phones. You can have mobile sets for the voice over I P phones that can be handled anywhere inside the building. The flexibility is another attraction in the wireless network. It enables the ease off, set up and change. You do not need toe fix wires inside the place. You do not need toe change the infrastructure. I mean the civil infrastructure of the place you do not need toe big inside the wall to fix cables. You do not need wiring hassles. You can enable the guest excess inside the place. The guest that is temporary inside the place and passing some time inside the place can be enabled through the wireless network you can allow to work remotely. You can allow toe access any server remotely from another place where the server room is away from you allow for freedom of operations you can separate. The person's working in different departments in different rooms, and they can still connect to each other wirelessly and connect to the network wirelessly. It allows freedom, which is some sort off mobility and some sort off flexibility in changing the place in the set up of the place. In that movement, off persons using the network wireless networks allows for scalability. You can expand the network easily. A machine can enter or leave the network easily, much more easier than the wired infrastructure. You have saved cables. You saved connecting devices such as the switches and routers. You saved them and replace them by a wireless excess point. You saved the outlets that exist in the world to connect the cables to the wired infrastructure. There are no outlets here in the wireless network. It is just the access point that connects wirelessly toe the other devices. You can easily add a machine toe. The wireless network you do not need toe. Add an outlet in the wall for this extra machine or to remove an out in the wool. If this machine leaves, this machine can be handled by a person who can enter the place and added to the network so easily and can leave the place and removed from the network with the same easiness. Scalability also means that you have the capability off relocation. Inside the building, you can change the functionality of any room from a meeting room, toe, an office or vice versa. You can have less planning overhead. You do not need to plan the room from the beginning until the end to be a meeting room. It can be a meeting room for some time and then an office, an ordinary office for the rest of the day, so it it does not need to be planned to be something that is fix it. Scalable speed off connection. The speed off connection for this network is scalable. It can be adapted toe the variety of devices connecting can be adopted. Toe the first mobile phone if it is smart and toe the slow mobile phone or laptop. If it is something old model, you can connect the hard to reach areas. The areas that can be hardly connected through with a wired infrastructure can be easily Richard through the wireless network, and through that excess point, you can enable here the concept off. Bring your own device with you to the place We have variety of devices laptops, mobile phones, tablets that can be brought to the place toe. Connect to the wireless network and you have ease off nattering establishment. Inside the meeting room. Inside the training center inside an office inside the canteen. Just connect the wireless excess point. So the sealing off this room and it is now a separate network and also a connected networked with a wired infrastructure through one excess point that connects these devices , toe the wired infrastructure and enables these devices to move and receives the wireless signals emitted from these devices. Toe their excess point and toe the world infrastructure and so forth. Wireless networks are cost effective. You save the coast off cables, you save the coast off connecting devices. You save the coast of outlets. You save the post off so many switches with somehow cheaper excess points and somehow less in number excess points. You save the Labour Coast that are involved in wiring. You save the labor costs that are involved in digging the wall and spreading the wild infrastructure inside the walls. Off the building, you save some civil work that is needed toe. Allow for the cables to pass inside the building toe. Cut the walls and the floors and the ceilings toe allow or toe. Establish a path for the cables toe pass through inside the building. You save all of this and you save the post off course off the devices, the end devices as well, since your guests or your trainees or your conference at in these can bring their own devices their own mobile devices into your premises, connect to your network and then take their devices back so you do not have to buy them any devices and to offer them any devices on your own. If we have a very small comparison between the wired and the wireless infrastructure, we can say that the wireless has many advantages, but it is not a perfect solution. We must mix both technologies in the network wired and wireless. The excess point just connects the wireless devices through the wire. The infrastructure. You must have a word core network and a wireless access network connecting the communicating devices toe the wired core infrastructure. A world infrastructure must exist at most of the cases toe be the infrastructure of the place, and Toby routed and toe be connected to the Internet. And then it can end with wireless terminals that can be mobile and can be moving inside the place. Wireless has advantages in offering a healthy environment inside the place. It avoids the electromagnetic interference. It avoids being shocked by the electrical signals traveling inside a wire. It saves all of this and offers somehow a healthier environment inside the place. It offers a safe premises for working because no falling over cables inside the place will take place or will occur, and you will have less cables mixing with water in the cleaning process. In the water flooding process, you will have less dangerous situation, since cables are less so. If there there is water existing inside the place, you will find that less cables are susceptible to mix with them and less people are falling over the cables existing in the place. Thank you. 17. Wireless Networks Types: Now let's take a look about on the wireless networks types. We have several types of wireless networks that are used in communications, so our course will focus on the WiFi network. But we can explore some types of the wireless networks that can be used in connecting devices and communicating them toe the Internet. The difference between each off the wireless networks mainly lies in two features. It's the frequency range that is used by this wireless network and the covered area that is used by this wireless network, the frequency range used by this wireless technology and the covered area by this technology, the bend with the distance, the speed are the main features that differs one wireless technology, then another. We have a variety of wireless technologies that are used in our daily life, such as the radio and television. Either tourist, aerial or satellite radios can be terraced Ariel and can be from the satellite. The same is the television, so both can be emitted from terrestrial stations or from the satellite in the sky. We have the G M. D. S s, which are used by ships to transmit their information and even their signals off emergency from the oceans. Toe the land we have in each country, the police and or be walkie talkies and wireless network to communicate through each other as persons from the police or the Army. In a safe and on a separate network. We have the airplanes that uses the networks to transmit signals between the civil airplane and the airport or the military airplane and the airport. We have the GSM, the global system mobile for the mobile phones and the smart mobile phones we hold in our hands. We have the Bluetooth technology that is used for transferring data in small geographical areas. We have the infrared that are used by the remote controls. We have the Y mix, which is a when technology for transferring data. And finally we have the WiFi, which is a land technology for transferring data, and the WiFi is the core off our section. Here. Let's talk about the frequency ranges. We have a license, that band and on I s and bend a license. That Ben means that you need a license to use this bent for your communication, a license from the regulatory authority existing inside your country to be able to transmit and receive signals over this band, and you have the eyes and band that can you be used for industrial scientific medical. That's what Isom stands for. Industrial, scientific and medical applications without the need for obtaining license. The WiFi lies in the ice and band. Many wireless technologies are inside the ice M band that can be used in transmission and receiving signals without the need off licensing from the regulatory authority, any regulatory authority inside a country is responsible off the spectrum. Management off this country is responsible off dividing the frequency range inside this country. Among the authorities that has been mentioned in the lost slide among the military and civil among the ah satellite and tourist area. Red Radio and television, too, avoid interference and toe save some door band between the frequency range is used for the different applications existing inside the country. All through the regulatory authority is responsible for quality monitoring, off mobile phone calls, off satellite communication and satellite television and satellite trade. You it has the authority off requesting from the mobile operators toe handle the phone calls in a better way or to offer better voice quality for their mobile phone calls. It is responsible for the rules and regulations toe offer fair play game between the mobile operators, for example, or between the video services companies that are offering video services over wireless networks. Each regulatory authority inside any country should have the research and development department that are responsible for funding and directing the research and development inside this country in the wireless communications domain and ask them for the up today technologies and the most reasoned ah research is that has been done over this type of communication. Let's have a look at the global system of ill, and the GSM is a very important component off the Internet nowadays, so many mobile devices connect to the Internet fruit, the GSM network. So we need to know more about this GS another. Let's have a look at this diagram and see that the laptop or the mobile phone is connected wirelessly. Toe the BTS BTS is something like a tower that exists in the street, and it is fix it, but it is covering it's surrounding area toe. Allow the mobile phones and laptops to connect wirelessly through it to the world infrastructure that is behind it. So the BTS is a very important component to be spreading over the whole area that needs to be covered by the wireless network. It allows for the mobile devices, the moving, moving devices inside the place to connect through it, do with a wild infrastructure. We have the PST, PST and network, which is the public switched telephone network. That is the world, not we're connecting the land phones there, fix it phone lines. And we have the Internet. That may use the infrastructure off the mobile network and the PST, another to connect mobile devices and fix the devices to the Internet, to the servers of the Internet to the World Wide Web. So we have the Internet as the largest network in the world and the network of networks that can allows the excess to mobile devices through the mobile at work or to fix the devices through the PST en tow. The World Wide Web network, the GSM, has passed through several generations. We have the first generation, second that our generation 3rd 4th and fifth and we have the lt which is the long term evolution. The main difference between each generation and the other lies in the bend. With the speed of connection, each generation is better in its speed and allows for more applications and more security features from a generation toe. Another. In the fourth generation, we can have a look at some video communication that can exist and that wells not there in the third or the second generation off Moviles. We can see in the fourth generation more security features and as well we can see the fifth generation that is still coming and in progress, having more bandwidths and more availability for video communication and more security features than the fourth and the third and the second generations, the Bluetooth. The Bluetooth is a very common way to connect some mobile devices that are not so remote in distance. It's a standard for short distances that can reach 10 meters or something like this. It uses short wavelength is that lies in the eyes and band industrial scientific medical bend, which means that using Bluetooth needs lower no license. You can establish a personal area network using the blue tooth personal area between two or three or more mobile devices, smartphones that are equipped with Bluetooth guards toe communicate with each other. Using this technology in a limited area, the Bluetooth is managed by the special interest group as I G off Bluetooth. It has the standard number, 802.15 from the I Tripoli. Bluetooth is acceptable to barriers and walls, which means that if two devices needs to connect to each other using the blue tooth, there should be no walls or barriers between them. If they will connect through Bluetooth, otherwise the connection will fail. The infrared is a very known way for wireless communication. It uses the electromagnetic radiation it uses longer wavelength is than the visible sight, the visible light. It is a short range communication. It is most commonly used by remote controls to switch between channels and things like this for any device, any electrical device or any device that he needs to be controlled remotely. Their infrared is just like the Bluetooth is susceptible to barriers and walls. And if there is a barrier or wall between the remote control and the device needs to be controlled, that communication fails. The Rhyme X, which is another form of wireless communication. It is a went technology. It is invented, and I mean it is managed by the climax forum. It has the standard number 802.16 from the I Tripoli. Why I'm extends for worldwide interoperability for microwave excess. It is competing now with the Lt or the long term evolution as a when technology. They are both competing now, as when technologies connecting devices with better speed with higher capabilities with more security features. The why Max can provide the triple play communication. And let's explain what is triple play. The triple play is allowing for data, voice and video to exist over the same connection over the same wire over the same outlet inside the building, which means that you receive the three off these information streams through one outlet, and this outlet is then spreading toe several devices. One outlet for the fix it phone for the voice, another outlet for the laptop for the Internet and the third outlet for your television. Four streaming video video on the men, for example, to your television. So the why Max can enable this triple play communication. Triple play communication is one off. The trends in communication toe enable all off the communication channels to co exist with each other inside one channel and with one outlet toe the user. Thank you. 18. Wireless Networks Protocols: Now let's talk about the wireless networks protocol. The WiFi. The WiFi stands for wireless fidelity. It's a land protocol. It is usedto connect. The virus is in the limited geographical area wirelessly. It has the standard off 802.11 from the I Triple E. We have several standards for the WiFi A, B G and then are the names of these standards. They differ in the frequents used and the speed achieved for the wireless communication. The WiFi generally works in the ice and bend, so it needs no license from the regulatory authority. It uses the frequencies off 2.4 gigahertz and five gigahertz, according to the Standard. Either it is a B, G or N. This frequency band is divided into a number of channels with a guard frequency or a guard band between each channel and the other. These channels are used for the communication off excess points that are near to each other without allowing for interference between their frequency ranges. WiFi is governed by the WiFi alliance. The 802.11 standard is the wireless land standard. If uses air as the transmission media, such as the rest off the wireless standards. It is concerned with the two lower layers off the S. I model the physical and the datalink layers in the datalink. Clear. It divides the Datalink lair into two sub players. One of them is the logical in control layer, and the other is the medium access control layer, and the physical air is also divided into two sub layers. One of them is called the Physical Layer Convergence Procedure PLC P. The other is the physical, medium dependent PMD layer. So we have in this diagram this division toe, the datalink and physical air. According toe the WiFi standard. We can establish two types of wireless networks amazed on the WiFi standard, either an infrastructure network or ad hoc network. The infrastructure not accuses the excess point to communicate to devices to each other. It is a start apology. It is more commonly used to establish a wireless network inside an office meeting room or corridor is, or something like this. The excess point is used to connect the wireless devices toe the wired infrastructure. Sometimes you need toe establish an ad hoc network wirelessly. You need to establish direct communication between two laptops or two mobile phones that happened to exist in the same place. This ad hoc network is established for short period inside, for example, a meeting inside the meeting room between two persons that need to communicate their business cars or to exchange some information between their laptops. They can do this using the ad hoc network. It's suitable for meetings and conferences. It is more flexible in set up. It can be set up for some short period of time and then dissolves. If these two laptops or mobile phones are away from each other, it uses the point to point communication topology. Meanwhile, the infrastructure, while it's not, loses the star topology. Since there is a connecting device, which is the excess point, the SS i D. Which is the service set identifier. This is the name off the network. This is the name that you can see when you scan the surrounding area. For wireless networks, it is used to identify the wireless than it is the name off. The I understand that you choose to connect toe. It can be broadcasted name or hither name, according toe the configuration off the excess point and the wireless. Then the configuration says that this wireless land is brought costed. Anyone that scans the network using that mobile device or the laptop can see the name of this network or it can be hidden. So scanning the network does not show this name. If you will connect to a head a network, you need to know to pieces of information, the name of the network and the password. Meanwhile, if you will connect to a broad cost that S s I d. You need only to know the password and you will find the name Broad Constant and you just click on it. Toby connected the length off the S S I d can reach to 30 toe alphanumeric characters. This is the name of the Notre Can reach 32 alphanumeric characters. It can be composed off several excess points. Several excess points can serve the same s s I D can connect devices toe the same as us. I d single excess point as well can connect to several SS ideas according to the conflagration off this excess point, it can connect devices toe. Many assess ID's many names off networks through the same excess point in WiFi collisions are avoided through another technology that is different from the Cisma CD. It is called the Cisma. See a carrier sense multiple excess collision avoidance. It uses two types of messages that are called RTs, which is request to send, and another signal that it's seat us. What happens is that descending device sends an RTs signal. It does not start sending all till until receiving city a signal from the receiving device . That's the way it avoids collisions. But the possibility off collisions still exists. There can be some pollutions. And as you know, collisions are something that we do not like over our networks, either wired or wireless. So collisions leads to poor performance, slower performance and leads to resending several times for the same type off information recovery off collisions is done just simply by resending the information that has collided with each other. Resending means slower. Resending, needs poor performance. But this is the way that this is messy. A depends on tow. Avoid collisions or to recover from collisions that already has happened By now we have introduced the WiFi protocol briefly. Thank you 19. Wireless Networks Devices: Let's now talk about the wireless networks devices. What are the devices that can communicate wirelessly? Let's start by the wireless excess point. The wireless Excess Point is a networking hardware device, as shown in the picture. It connects the mobile devices toe the wild infrastructure from one side. It is connected toe the registration jack 45 to the other side it is connected to an antenna. So this antenna is used for wireless communication, and the RJ 45 is used as an Ethernet interface for the wired infrastructure. So it has the interfacing between the wild infrastructure and the wireless network through the antenna and the Audrey 45 existing in the same device. The access point is a layer to device. It works in the physical and datalink layers. The coverage area depends on the antenna on the number of antenna existing in this wireless excess point and the strength of each off its antenna. Off course wireless excess point with one antenna covers less area than wireless. Excess point, with two and two is less than four and four is less than six and off course. Each. Anthony has its strength and its coverage area. So the antenna, its number and its strength determines, to a great extent the coverage area off this wireless excess point. We have several excess points manufactured by several known vendors for networking devices . Cisco and other companies has produced a very well known names for excess points such as Huawei and other networking companies. It may contain a DSL and router in the same box. This is a wireless point for home connections, the one that contains the SL and the router. It is a variety off devices that are contained inside one box, so this DSL is connected toe the telephone line and the router is connected toe. They're splitter, and then each of these devices interact toe. Get the wireless device inside your home connected to the Internet. The water's excess point can support several standards off the WiFi, A BG and and standards. It can be divided into several radio channels to avoid interferes between the channels, it is communicated with each other. This excess point can act on Channel five, and the adjacent excess point can act on Channel seven, so we leave Channel six in between unused so as to avoid interference between the communication challenge. One excess point can hold several SS ideas, either broadcasted or hidden. The speed and coverage of the excess point depends on the brand and model off the manufacturers. A good one can cover bigger area and can have a hard speed. The excess point signals can be obstructed by wolves and can be ah, stopped by by long distances. This wireless signals can be reflected by walls and cannot bypass walls, and did is susceptible toe being weakened through long distances. It can be configured through its firmware directly through tell not, for example, or any other communication that can directly sets the configuration and saves the configuration over the firmware or the configuration can be Web based. The excess point can show a Web interface that can be used by the user toe. Configure it to determine the channel to determine their encryption protocol that will be used by this excess point and other settings. For this excess point, the excess point can receive its power over the ether ether lad connection. It can use the power over Ethernet concept Toby powered. If it is in the ceiling or in some place, that is hard to connect power to it. The security features inside the wildest excess point are many. The S S I D itself can be hidden so it is not exposed to the attacker. Excess once used filtering based on several parameters, it can filter the traffic based on Mac addresses or based on I p addresses or based on port numbers, which means that it can filter that http service. Based on Port number 80 it can filter some domain names to access the network from inside to outside or vice versa. Excess points use encryption techniques to communicate between the device and the excess point. The mobile device and the excess point can transmit and receive signals using the Web wireless encryption protocol, the W P. A or the A s protocols. Those three are encryption protocols that are used to encrypt the traffic between the wireless excess point and between the communicating mobile device wirelessly. The A s is the most recent encryption protocol among these three. Let's have a look at the configuration off wireless excess point. This is the configuration page. This is the page that appears when configuring the excess point through Web interface as you can see you can enable villain. You can determine the SS i D. You can determine the operation mode. You can determine the channel of communication, and you can from the media on the left. Determine the security features that you want to apply over this wireless excess point. Namely, you can determine the Mac filtering, which make addresses to filter and which make addresses to pass, which I P addresses the filter and which I P addresses to post and which domain names the filter and which domain names the path you can monitor the throughput. You can have statistics about the wireless communications, and you can have several features toe configure through this excess point. Using that Web interface speech, let's have another device that can connect your network wirelessly, which is the USB modem. It connects species laptops through the GSM network via mobile operator so it is inserted inside the PC or the laptop toe. Connect this PC or laptop toe the mobile operator company through the GSM letter. It depends on the network generation, so the speed can either be three G or can be faster using the four G or anti network. It needs no world infrastructure. It can be inserted inside the laptop with no wired infrastructure to connect this laptop toe that Internet directly through the wireless infrastructure. Off course, this USB modem has charging fees according to your subscription toe, your mobile subscriber and your mobile letter. You should pay for this traffic passing through the GSM network your subscribed toe. So it is ghostie than the WiFi network. It has less network speed than the WiFi, and it uses more power off that mobile device, such as the laptop or smartphone, more power than the WiFi. It allows more flexibility and mobility says it can be connected anywhere covered by the mobile network and the mobile operator. So it allows more flexibility and mobility. And it can be connected through streets and through remote areas just covered by the mobile network Operator Smartphones are the terminals that are most commonly connecting toe. The wireless network, Smart fourth and laptops are the in terminals. In a wireless that work, it's spreading fast over the world. We have so many statistics that says that smartphones are penetrating that markets off several countries, and it is increasingly spreading over the world in number and in the type and number off users. It can be connected to the Internet through WiFi. It can be connected through the GSM network. It can be connected to other more mobile devices through the Bluetooth. It can also act as hot spot that can can connect other devices through it to the Internet can act as the excess point for other devices to the Internet, and this excess point can connect them through the GSM network. WiFi is less battery consuming, then GS and in smartphones. If you connect through your smartphone toe WiFi and connect to the Internet, you will consume less battery than connecting to the Internet. Using the GSM network charges four Gs and depends on your subscription. You either pay a monthly subscription and uses the Internet according to the subscription, or you can either pay as you go pay. As you download Perez. You pay as you use for the GSM operator. You are subscribed toe and use whatever services you can use offered by this mobile operator. Thank you 20. Wireless Networks Drawbacks: Now let's know some off the drawbacks off the wireless networks and answer some of the review questions over thes two sections. The wireless networks Throwbacks lies in the limitations in the coverage. The areas covered by the wireless network is obstructed by wolves and long distances and sometimes weather conditions, such as in satellite communications and things like this. So wolves can obstruct the signals and can cause attenuation and can cause reflection and refraction for the wireless signals. Long distances can cause very strong attenuation for the wildest signal and may make it very weak. Toby heard correctly and to be utilized at the end device. The weather conditions can act as, AH, weakening for the wireless signal as well, and reflection and reflection. And such conditions can be obvious in the satellite communication. The wireless network generally has a higher bit rate higher than the corresponding wire network. Wireless is in general less in the security features. This is because the communication media is the air. It is open for sniffing. It is susceptible to any listening device that can catch the signal intended from a certain sending device to a certain receiving device and interpreted and no, its content because it is just in there, which is open for everyone. So sniffing is probably very highly probable. Sometimes the wireless network is very coast ian, charging like the GSM like the USB modem, which uses the GSM network. So it depends on your subscription. Either you are monthly subscribed or you pay as you go so it can be caused the than the wired network. It cannot fully replace the world infrastructure. The wireless network is to serve the mobility and the flexibility goals only, but it is hard and very rare to find another that is completely worlds. Even the mobile network. The mobile operator network, is wireless only in the excess network, but it is wired in the court. Many, many networks act like this. It is wireless at the exercise toe, offer mobility and flexibility what it is wired in the core toe connect and to communicate between the fix it devices, the fix it, connecting devices, forming this letter. Now let's have some review questions. What is the standard protocol over the Internet? It's the TCP I P Protocol. What does d c P i p stand for T c P. I P stands for transmission control protocol. Internet Protocol. Many, many people studies this protocol and ignores knowing the meaning and knowing what does it stand for? And let's figure out here that the TCP i p the word off the protocols so it is composed off the two most important protocols forming it. The TCP Protocol in Layer four and the I P Protocol in Layer three that were clear. What are the layers off the TCP I p. It's application, transport, Internet or networking and knocker access. As you can see only four layers. It is not like the always I composed off seven layers. Some names are common, like the application, transport, Internet or network, and some names are not common like the Network Texas. Let's recall here that the network excesses formed off the physical and datalink layers of the eyes. O s I. The Internet is the same as the network layer. The transport is the same as the transport layer in both in the S I modern. The application here in the TCP I p is corresponding toe three layers in the argo a Simon, the application, the presentation and the session layer seven and Layer six and layer five in the Arzo Asai model are here corresponding toe one layer in the TCP I P, which is called the application layer. This is very important to record name some off the application layer protocols in TCP I p. We can name several protocols working in the application layer off the TCP I P such as the http hypertext transfer protocol, the FTP, the file transfer protocol, the end as the domain name system protocol and the SMTP the simple mail transfer protocols . All of these are working in the application layer off the TCP I p. Let's hear recall that the application layer off the TCP I p is corresponding toe three layers off the Arzo Asai Modern, which are application, presentation and session. What are the port numbers used by each of the above protocols, respectively. Let's recall here that http use a sport number 80 ftp uses port number 21. The Enos uses fourth number 53 it can act either TCP or UDP as empty. P uses sport number 25 these port numbers our identifies that exist in the transport layer that identifies the type of service requested from that line toe the server toe, identify the type of data that needs to be transmitted between both machines. Http transfers text images and hypertext FTP transfers, files the N S. Transfers domain name queries and replied to result between i p addresses enemy names. SMTP is for the exchange off emails between the mail servers and between the mail servers and email clients. What is the lens off the I P address in bits? What is the length of the I P addresses? It's 32 bits in version four and 128 bits in Virgin. Six. This is the length of the I P address. Let's record here that the I p address is a unique identifying, logical identify are bound to the geographical location off the machine. What are the device is working in Layer three are or what could be. The device is working in layer three. The router is the most common device working in layer three and layer three switches are another type of devices working in layers. Three layers. Three switches are somehow faster. It uses the hardware toe to perform the routing function. How can the routing table build inside the route. It can be build. Eyes are static, statically by the admin entered by the admin off the network in tow. The router or the router can build it dynamically through some routing protocols that X dynamically through some dynamic routing protocols, such as the routing Information Protocol R. I. P. Or open Shorter's tests first protocol, which is oh, SPF and other protocols that can act dynamically to build the routing table. Inside that out. What are the main advantages off a wireless network? Many advantages off wireless flexibility, mobility, scalability and other advantages for the wireless network over the wild. But let's remember here that the network can be composed off mixer technologies, wired and wireless wireless to offer flexibility, mobility and scalability and wire to connect this world less network toe the wired infrastructure, in which layer does the weap work. The Web is the wireless excess point. It works in layer toe, the Datalink lair. It works in both layers, the physical and the detailing. But it is a layer to device what are the main throwbacks of wireless networks. We had some drawbacks. Its limitations in the coverage area do toe the obstacles off walls or weather conditions, or sometimes the long distances that can at anyway, the signal being transmitted. The sniffing, its security vulnerability in the world isn others. It allows four sniffing off the data being sent from the sunder to the receiver because that transmission media is open for everyone, it is simply the air that can be sniffed by anyone, and the message that is intended to a certain recipient can be interpreted and received by another recipient that was not intended. This is off course, a security hole or a vulnerability. Ah, the wireless networks in general have higher beat a retreat than the wild ones. And by this we come to the end off our wireless section. Hopefully we have briefed many off the wireless concerts. Thank you.