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Unit 1: Computer Networks Dr. Jahangir Alam, University Women's Polytechnic Notes

Unit 1: Computer Networks Dr. Jahangir Alam, University Women's Polytechnic Notes

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Unit 1: Computer Networks Dr. Jahangir Alam, University Women's Polytechnic Notes

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  1. UNIT 1: Introduction to Computer Networks Computer Engineering Section University Women’s Polytechnic Aligarh Muslim University, Aligarh February 5, 2020 Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 1/113

  2. Outline Computer Networks: What and Why?? Applications of Computer Networks Types of Network Connections Categories of Networks: LAN, MAN & WAN Network Topologies Network Configurations: Server Based, Peer-to-Peer & Hybrid Expanding Networks Network Segmentation Types of Servers Network Performance Parameters: Bandwidth, Throughput, Latency, Jitter etc. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 2/113

  3. Computer Network & Networking A Computer Network is a set of autonomous comput- ers and other devices connected together to exchange infromation and sharing resources. By autonomous we mean that no computer on the net- work can be forcibly start/stop by any other computer on the network. Another definition is - A group of computers and other devices connected together is called a network and the concept of connected computers sharing information and resources, is called Networking. Each device on the network is referred to as node. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 3/113

  4. Centralized Computing Vs. Networking I In centralized computing there is a computer with single powerful CPU and a number of terminals are connected to it as shown in the figure on slide 6. All processing is performed within the boundaries of the same physical computer. User terminals are typically dumb ones, incapable of functioning on their own. They are cabled to the central computer. Sometimes these terminals have very little processing power and memory of their own and are called intelli- gent terminals. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 4/113

  5. Centralized Computing Vs. Networking II This architecture places the tremendous burden on the central computer. In recent years, there have been significant advances in the development of high performance personal comput- ers and networks. There is now an identifiable trend in industry towards downsizing, i.e. replacing expensive mainframe com- puters with more cost effective networks of personal computers that achieve the same or even better results. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 5/113

  6. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 6/113

  7. Why Networks?? Networks are all about: Sharing Resources. Preserving Information. Protecting Information. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 7/113

  8. Sharing Resources I Resource sharing means sharing H/W and S/W. Hardware Resource Sharing: Networked Computers can share: Printers, Fax Modem, Scanners, Hard Disks, Floppy Disks, CD-ROMS, Tape Backup Units, Plotters, Any device that can be attached to the Network. Software Resource Sharing: Software resources can be used more effectively over networks. With stand alone computers the software used on the computers must be present on each computer’s hard disk, whether or not that computer is used at that moment for the task the software performs. For a large number of stand alone computers S/W cost can become more than expectations. It is also difficult and time consuming to install and configure the S/W individually on each computer. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 8/113

  9. Sharing Resources II With a network we can install and configure the software on one com- puter (server) and can share it with other computers on the network. We can also control the access to that S/W. Not all S/W will use a network even if one is installed on the server. Dif- ferent S/W packages have different restrictions on how the software can legally be used on a network. We must check the S/W documentation to check what features the S/W provides in a networked environment. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 9/113

  10. Preserving Information Besides, information and resource sharing a network al- lows information to be backed up to a central location. Important information can be lost by mistake or acci- dentally when a stand alone computer has no backup means. It is also difficult to maintain regular backups on a num- ber of stand alone computers. In a networked environment when we take backup at a central location from all computers, we have one place to preserve it. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 10/113

  11. Protecting Information With stand alone computer, access to the computer means access to the information on that computer. Networks provide an additional layer of security by means of passwords. We can give each network user a different account name and password, allowing the network server to distinguish among those who need access to have it and protecting the information from tampering by those who do not. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 11/113

  12. Components of a Data Communication System I There are f ive components of a data communication sys- tem: 1 Message: The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video. 2 Sender: A sender is a device that sends the data mes- sage. It can be a computer, workstation, telephone handset, video camera, and so on. 3 Receiver: A receiver is a device that receives the mes- sage. It can be a computer, workstation, telephone handset, television, and so on. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 12/113

  13. Components of a Data Communication System II 4 Transmission Medium: The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 13/113

  14. Components of a Data Communication System III 5 Protocol: A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 14/113

  15. Transmission Modes I The term Transmission Mode defines the direction of the flow of information between two communicating devices i.e. it tells the direction of signal flow between the two devices. There are three ways or modes of data transmission: Sim- plex, Half duplex (HDX) & Full duplex (FDX) 1 Simplex - unidirectional, one can transmit other can only receive, uses entire capacity of channel to send data in one direction. Ex- amples of simplex mode is loudspeaker, television broadcasting, television and remote, keyboard and monitor etc. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 15/113

  16. Transmission Modes II 2 Half Duplex - both station can transmit and receive but not at the same time, entire capacity of the channel can be used for each direction. Example of half duplex is a walkie- talkie in which message is sent one at a time and messages are sent in both the directions. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 16/113

  17. Transmission Modes III 3 Full Duplex - both stations can transmit and receive simultane- ously, either separate channels or channel can be divided between signals traveling in both directions. Example of Full Duplex is a Telephone Network in which there is communication between two persons by a telephone line, through which both can talk and listen at the same time. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 17/113

  18. Classification of Computer Networks There is no generally accepted taxonomy for computer net- works but two criteria based on which they can be classified are Transmission Technology and Scale. Based on tramission technology they may be classified as: Broadcast/ Multipoint Networks Point-to-Point Networks Based on scale (physical limits) they can be classified as: Local Area Network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN) Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 18/113

  19. Broadcast Networks I 1 Broadcast networks have a single communication channel that is shared or used by all the machines on the network. Short messages called packets sent by any machine are received by all the others. 2 Broadcast systems generally use a special code in the address field for addressing a packet to all the concerned computers. This mode of operation is called broadcasting. 3 Some broadcast systems also support transmission to a subset of the machines known as multicasting. 4 Upon receiving a packet, a machine checks the address field. If the packet is addressed to it then the packet is processed, otherwise the packet is ignored. 5 The channel’s capacity is shared temporarily among the devices connected to the link. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 19/113

  20. Broadcast Networks II Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 20/113

  21. Point-to-Point Networks I 1 A point-to-point connection is a direct link between two devices such as a computer and a printer. It uses dedicated link between the devices. 2 The entire capacity of the link is used for the transmission between those two devices. 3 In point to point networks, there exist many connections between individual pairs of machines. 4 To move from sources to destination, a packet (short message) may follow different routes. 5 In point-to-point connection, there can only be a single transmitter and a single receiver. On the other hand, in multipoint connection, there is a single transmitter, and there can be multiple receivers. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 21/113

  22. Point-to-Point Networks II 6 The switching nodes are not concerned with the contents of data. Their purpose is to provide a switching facility that will move data from node to node until they reach the destination. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 22/113

  23. Classificaton Based on Scale I Local Area Networks (LANs) A Local Area Network (LAN) is a network that is restricted to smaller physical areas (few kilometers - typically upto 5 kms) e.g. a local office, school, house, University campus etc. On a ‘Local Area Network’ data transfer speeds are higher than WAN & MAN, and that can range from 10.0 Mbps (Ethernet network) to 10 Gbps (10 Gigabit Ethernet). A LANs is usually implemented using any of the LAN Technolo- gies i.e. Ethernet, Token Ring and FDDI (Fiber Distributed Data Interface). LAN Technologies are also referred to as Physical and Data Link Layers Protocols. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 23/113

  24. Classificaton Based on Scale II Local Area Networks (LANs) Each LAN technolgy offers specific devices (meant for that technol- ogy only) and network layouts (topologies) for connecting several computers as LAN. The most prevalent LAN Technology is Ethernet. It is standardized as IEEE 802.3. The most common forms of Ethernet are 10BASE-T, 100BASE-T, and 1000BASE-T. All three use twisted pair cables. They run at 10 Mbit/s, 100 Mbit/s, and 1 Gbit/s, respectively. Fiber optic variants of Ethernet are also very common in larger networks, offering high performance and longer distance (tens of kilometers with some versions). Also referred to as WiFi, Wireless LANs (WLANs) are standardized as IEEE 802.11. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 24/113

  25. Classificaton Based on Scale III Local Area Networks (LANs) In general, network protocol stack software will work similarly on all varieties. LANs are restricted in size. It simplifies network management. They are more reliable as compared to MAN and WAN. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 25/113

  26. Metropolitan Area Network (MAN) I A Metropolitan Area Network (MAN) is a network that connects two or more computers, communicating devices or networks in a single network that has geographic area larger than that covered by even a large ‘Local Area Network’ but smaller than the region covered by a ‘Wide Area Network’ (Typically from more than 5 km to 160 km). A Metropolitan Area Networks bridges a number of ‘Local Area Networks’ with a fiber-optical links which act as a backbone, and provides services similar to what Internet Service Provider (ISP) provide to Wide Area Networks and the Internet. MANs can bridge Local Area Networks without any cables by using microwave, radio wireless communication or infra-red laser which transmits data wirelessly. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 26/113

  27. Metropolitan Area Network (MAN) II Distributed Queue Dual Bus (DQDB) is the Metropolitan Area Network (MAN) IEEE 802.6 standard for data communication. Using DQDB, networks can extend up to 100km-160km and op- erate at speeds of 44 to 155Mbps. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 27/113

  28. Wide Area Network (WAN) I Wide Area Network is a computer network that covers relatively larger geographical area such as a state, province or country. It provides a solution to companies or organizations operating from distant geographical locations who want to communicate with each other for sharing and managing central data or for general com- munication. WAN is made up of two or more Local Area Networks (LANs) or Metropolitan Area Networks (MANs) that are interconnected with each other. In ‘Wide Area Network’, Computers are connected through public networks, such as the telephone systems, fiber-optic cables, and satellite links or leased lines. The ‘Internet’ is the largest WAN in the world. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 28/113

  29. Wide Area Network (WAN) II WANs are mostly private and are build for a particular organization by ‘Internet Service Providers (ISPs)’ which connects the LAN of the organization to the internet. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 29/113

  30. Other Special Types of Networks I 1 Home Area Network(HAN): As the name would suggest, a HAN is the connection of network enabled devices in a domestic home. 2 Personal Area Network(PAN): As the name suggests, a personal area network is intended for personal use within a range of a few ten meters. Mainly, the technologies used for creating personal area networks are wireless. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 30/113

  31. Other Special Types of Networks II A notable example of WPAN is the Bluetooth technology, mostly found on portable devices like smartphones, laptops, tablets, wearables, etc. Other PAN technologies are Zigbee, Wireless USB, etc. Wireless BAN can work together with PAN technologies. For instance, a Bluetooth-connected smartphone can be used to sync data from wearables and various sensors present in the body. 3 Body Area Network(BAN): You can create a body area network by using wearable devices like smart- watches, fitness bands, biometric RFID implants, and medical devices placed inside the body like pacemakers. Wireless BAN is the primary form used to created such networks. It is defined as per the IEEE 802.15.6 standard which describes a short-range, extremely low power wireless communication within or in a vicinity of the human body. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 31/113

  32. Other Special Types of Networks III 4 Near-me Area Network(NAN): A near-me area network (NAN) is a communication network that focuses on wireless communication among devices in close proximity. Unlike local area networks (LANs), where the devices are in the same network segment and share the same broadcast domain. The devices in a NAN can belong to different proprietary network infras- tructures (for example, different mobile carriers). If two devices are geographically close, the communication path between them might, in fact, traverse a long distance, going from a LAN, through the Internet, and to another LAN. Remember chatting with your friends on Facebook while all of you were sitting in the same room. You were part of a NAN, even though you might be on the networks of different carriers. A message from your device would traverse all the way to Facebook servers over the internet come to your friend’s device sitting right next to you. In a logical way, both the device are on some sort of network. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 32/113

  33. Other Special Types of Networks IV 5 Storage Area Network(SAN): SAN is a high-speed network of storage devices that also connects those storage devices with servers. It provides block-level storage that can be accessed by the applications running on any networked servers. Block-level storage is a type of storage in which each block (consisting of several hard drives) of the storage system can be controlled as an individual hard drive, and the blocks are managed by a server operating system. SAN devices appear to servers as attached drives Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 33/113

  34. Other Special Types of Networks V 6 Campus Area Network(CAN): A network infrastructure covering the school, university, or a corporate premises can be dubbed as campus area network. It can comprise of several LANs and connected to the internet using a leased line or any other means. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 34/113

  35. Other Special Types of Networks VI 7 Virtual Private Network(VPN): A virtual private network (VPN) is a private network that is built over a public infrastructure. VPN is a type of computer network which doesn’t have physical exis- tence. The devices that are part of a VPN could be present anywhere on the earth, connected to each other over the internet. Security mechanisms, such as encryption, allow VPN users to securely access a network from different locations via the Internet. VPNs are used by corporates to interconnect their offices located in different places and give their remote employees access to company’s resources. It has phased out another type of network known as Enterprise Private Network, a physical network created by organizations to link their office locations. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 35/113

  36. Network (LAN) Topologies I A network topology is the arrangement of a network, including its nodes and connecting lines. There are two ways of defining network geometry: the physical topology and the logical (or signal) topology. On a network the way in which connections are made is called the physical topology of the network. Physical topology specificaly refers to the physical layout of the network, especially the locations of the computers & devices and how cable is run between them (Geographical arrangement of com- puters, devices and cables.). Logical (or signal) topology refers to the nature of the paths the signals follow from node to node. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 36/113

  37. Network (LAN) Topologies II In many instances, the logical topology is the same as the physical topology. But this is not always the case. For example, some networks (e.g. Hub based star and Token Ring) are physically laid out in a star configuration, but they operate logically as bus or ring networks. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 37/113

  38. Physical Network (LAN) Topologies I 1 Bus Topology On a bus network, the cable is just one or more wires, with no active electronics to amplify the signals or to pass them from one computer to another. This makes the bus a passive topology. When one computer sends a signal up (or down) the wire, all the other computers on the network receives the information. But, only one (the one with the address that matches the address en- coded in the message) accepts the information. The rest discard the message. Only one computer at a time can send the message. Therefore, the number of computers attached to a bus can significantly affect the speed of the network. A computer must wait until the bus is free before it can transmit. These factors also affect star and ring networks. Another important issue in bus network is termination. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 38/113

  39. Physical Network (LAN) Topologies II As the bus is a passive topology, the electrical signal from a transmitting computer is free to travel the entire length of the cable. Without termination, when the signal reaches at the end of the wire, it bounces back and travels back up the wire. When a signal echoes back and forth along an unterminated bus, it is called ringing. To stop signals from ringing we attach terminators at either end of the bus. Terminators absorb the signals and stop ringing. Ethernet 10Base2 (uses BNC T-Connectors with coaxial cable), also referred to as thinnet is an inexpensive network based on bus topology. Ethernet 10Base5 also referred to as thicknet is another network based on bus topology. It uses thick coaxial cable compared to one used in thinnet. Advantages Simple, Reliable for small networks, Easy to use and install. Requires least amount of cable and therefore less expensive. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 39/113

  40. Physical Network (LAN) Topologies III Scalable: Its easy to extend a bus. Repeaters can be used to boost the signals if a larger bus is required. Disadvantages Heavy network traffic can slow down a bus considerably. Problems caused by terminators. Difficult to troubleshoot. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 40/113

  41. Physical Network (LAN) Topologies IV Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 41/113

  42. Physical Network (LAN) Topologies V 2 Star Topology Each computer on a star network communicates with a central device. The central device resends the message to all computers (in a broad- cast star network(hub based)) or only to the destination computer (in a switched star network). The central device in a star network can be an Active Hub or a Passive Hub or a Switch. An active hub regenerates the electrical signal and sends it to all the computers connected to it (broadcast star network). Active Hubs and Switches require electric power to run. A passive hub such as wiring panel or punch-down blocks merely acts as a connection point and doesn’t amplify or regenerates the electrical signal. Passive Hubs don’t require electric power to run. We can use STP(Shielded Twisted Pair), UTP (Unshilded Twisted Pair) or Fiber Optic cables to implement star networks. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 42/113

  43. Physical Network (LAN) Topologies VI A hybrid hub/ switch can accomodate several types of cable in the same star network. Ethernet 10Base-T, 100Base-T (Fast Enternet), 1000Base-T (Gigabit Ethernet) and 10000Base-T (10 G Ethernet) are well known star net- works implemented with twisted pair cables (STP/UTP). In above star based ethernets, if medium (twisted pair cable) is replaced by Fiber Optics then ’T’ gets replaced by ’F’ (e.g. 10Base-F etc.). Advantages It is easy to modify and add new computers to a star network without disturbing the rest of the network. The centre of the star is a good place to diagnose network faults. Single computer failure do not bring down the whole star network. Several types of cable can be accomodated on same network. Disadvantages If central hub fails the whole network comes to halt. Expensive compared to bus based networks. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 43/113

  44. Physical Network (LAN) Topologies VII Active Hub and Switch consume electricity. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 44/113

  45. Physical Network (LAN) Topologies VIII 3 Ring Topology On a ring network, each computer is connected to the next computer with the last one connected to the first. Each computer retransmits what it receives from the previous computer. The messages flow around the ring in one direction. Since each computer retransmits what it receives, a ring is an active network and is not subject to the signal loss problem. There is no termination because there is no end to the ring. Some ring networks do token passing. In token passing, a short message called token is passed around the ring until a computer whishes to send information to another computer. That computer captures the token modifies it to adds an electronic address and data, and sends it around the ring. Each computer in sequence receives the modified token and passes it to the next computer until either the electronic address matches the address of a computer or the token returns to its origin. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 45/113

  46. Physical Network (LAN) Topologies IX The receiving computer sends an acknowledgement to the originator indicating that the message has been received. The sending computer then creates a fresh token and place it on the network, allowing other computer to capture the token and begin trans- mitting. This all happens very quickly. A token can circle a ring 200 meters in diameter at about 10,000 times a second. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 46/113

  47. Physical Network (LAN) Topologies X The topology of IBM’s Token Ring LAN technology (standardized as IEEE 802.5) uses the similar kind of ring. Physical topology of token ring is star but logically it is a token passing ring. Some other ring networks have two counter-rotating rings, that help them recover from network faults. The topology of FDDI (Fiber Distributed Data Interface) LAN technol- ogy uses two counter-rotating rings. Advantages No computer can monopolize the network as each computer is given equal chance of capturing the token. Token passing makes ring topology perform better than bus topology under heavy traffic. Disadvantages Failure of one computer on the ring can affect the whole network. Difficult to trobuleshoot. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 47/113

  48. Physical Network (LAN) Topologies XI Adding or removing computers disrupts the network. 4 Mesh Topology In a mesh network topology, each of the network node, computer and other devices, are interconnected with one another. In a full mesh topology, every computer in the network has a connection to each of the other computers in that network. The number of connections in this network can be calculated using the formula n(n − 1)/2, where n indicates the number of devices. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 48/113

  49. Physical Network (LAN) Topologies XII This type of topology is very expensive as there are many redundant connections, thus it is not mostly used in computer networks. Advantages Can handle high amounts of traffic, because multiple devices can trans- mit data simultaneously. A failure of one device does not cause a break in the network or trans- mission of data (fault tolerant). Adding additional devices does not disrupt data transmission between other devices. Easy to troubleshoot. Disadvantages The cost to implement is higher than other network topologies, making it a less desirable option. Building and maintaining the topology is difficult and time consuming. Becomes unmanagable as more and more devices join network. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 49/113

  50. Hybrid Topologies I In today’s networks we also see the combinations of the topologies of bus, star and ring. A topology which is created by combining two or more topologies is referred to as a hybrid topol- ogy. Some popular hybrid topologies are star-bus & star-ring. Figure on next page illustrates each of them. Dr. J. Alam (CES) Unit 1: Introduction February 5, 2020 50/113

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