Computer Networks Textbook Computer Networks 4 th ed

Computer Networks Textbook: Computer Networks 4 th ed. , by A. S. Tanenbaum 10/26/2021 Sam_CN_UNIT- I 1

COMPUTER NETWORKS Ch. Samson M. E, (Ph. D) Associate Professor & Associate Head, Dept of IT 10/26/2021 Sam_CN_UNIT- I 2

UNIT- I: INTRODUCTION What is a network? Set of devices communicating with each other l Could be a CPU, monitor and other peripheral devices connected (and exchanging data) to each other l Could be a group of people …. A network of friends l Or, could be a set of computers communicating with each other l 10/26/2021 Sam_CN_UNIT- I 3

Computer Network Technology and architecture of the communications networks used to interconnect devices l An interconnected collection of autonomous computers is called computer network l Examples: LAN, MAN, WAN, Internet etc. l 10/26/2021 Sam_CN_UNIT- I 4

Why Networks? Point-to-point communication is not usually practical because l Devices are too far apart l Requires large number of connections between all devices l Too expensive l Solution is a communications network l 10/26/2021 Sam_CN_UNIT- I 5

Uses of Computer Networks Availability of Resource / Resource sharing - Resources become available regardless of the user’s physical location l Load Sharing - Jobs processed on the least crowded machine l High Reliability - File and processor redundancy l Human-to-Human Communication - Telephone - Long distance education and collaboration l 10/26/2021 Sam_CN_UNIT- I 6

Applications of Computer Networks Business Applications l Home Applications l Mobile Users l Social Issues l 10/26/2021 Sam_CN_UNIT- I 7

Business Applications of Networks l The client-server model involves requests and replies Fig: A network with two clients and one server 10/26/2021 Sam_CN_UNIT- I 8

Home Network Applications Access to remote information - World Wide Web l Person-to-person communication - Electronic mail, Videoconference l Interactive entertainment - Video-on-Demand, Games l Electronic commerce l 10/26/2021 Sam_CN_UNIT- I 9

Home Network Applications l Some forms of e-commerce. 10/26/2021 Sam_CN_UNIT- I 10

Mobile Network Users l Combinations of wireless networks and mobile computing -Cellular Phones, Personal Digital Assistant (PDA) and Smart hones (PDA+ Handset+ GPS+…) 10/26/2021 Sam_CN_UNIT- I 11

Social issues l l l l Intrusions Privacy Copyright Pornography Anonymity Security Worms and Virus responsibility of the service providers 10/26/2021 Sam_CN_UNIT- I 12

Network Hardware Network design dimensions: Transmission technology( broadcast networks, Point-to -point networks) l Scale( LAN, WAN, Internet etc. . ) l 10/26/2021 Sam_CN_UNIT- I 13

Network Classifications Based on transmission technology networks are divided into Broadcast and Point to Point networks Ø Broadcast Networks use one communication channel that is shared by all the machines. Packets are sent to the shared channel and are “listened to” by all machines. (for smaller, geographically localized networks) l 10/26/2021 Sam_CN_UNIT- I 14

Network Classifications (cont’d) Ø Point - to - Point network : A network in which a physical communication path exists between 2 end-systems with no other devices involved 10/26/2021 Sam_CN_UNIT- I 15

Network Classifications (cont’d) Classification based on scale Local Area Networks( LAN): Room, Building /Campus l Metropolitan Area Networks ( MAN): City l Wide Area Networks (WAN): Country, Continent l Wireless Networks l Home networks l Internetworks: Global l 10/26/2021 Sam_CN_UNIT- I 16

Local Area Network in small geographical Area (room , building or a campus) is called LAN l A LAN is a data communication system allowing a number of independent devices to communicate directly with each other, within a moderately sized geographic area over a physical communication channel of moderate data rates. l 10/26/2021 Sam_CN_UNIT- I 17

Local Area Network (Cont’d) l l l Short geographical distance (a few kilometers) High speed (Larger than 1 Mbps up to 100 Mbps ) Multiple access (Many can use it at the same time) Sharing (hardware, software etc. ) IEEE standard 802. 3 The most reliable network 10/26/2021 Sam_CN_UNIT- I 18

LAN Topologies 10/26/2021 Sam_CN_UNIT- I 19

Metropolitan Area Networks Network in a City is call MAN (Metropolitan Area Network) l MAN is distinguished by its adopted standard DQDB (Distributed Queue Dual Bus (IEEE standard 802. 6) and it contains two unidirectional buses which all the computers are connected l A metropolitan area network based on cable TV 10/26/2021 Sam_CN_UNIT- I 20

Definitions l l l Network: Interconnected collection of autonomous computers Host: machine running user application Subnet: Communication subnet carries messages between hosts Channel: Logical Line of communication (circuit) Router: Network router is a device or a piece of software in a computer that forwards and routes data packets along networks 10/26/2021 Sam_CN_UNIT- I 21

Wide Area Networks Network spread geographically (country or across Globe) is called WAN. l WAN contains hosts that are connected by a communication subnet l The job of the subnet is to carry messages from host to host like telephone system carries words from speaker to listener l Store-and-forward network l 10/26/2021 Sam_CN_UNIT- I 22

Wide Area Networks (Cont’d) Fig: Relation between hosts on LANs and the subnet 10/26/2021 Sam_CN_UNIT- I 23

Wide Area Networks (Cont’d) Figure: A stream of packets from sender to receiver 10/26/2021 Sam_CN_UNIT- I 24

Networking Devices HUB, Switches, Routers, Wireless Access Points, Modems etc. 10/26/2021 Sam_CN_UNIT- I 25

Wireless Networks Categories of wireless networks: (used for) System interconnection l Wireless LANs l Wireless WANs l 10/26/2021 Sam_CN_UNIT- I 26

Wireless Networks (Cont’d) (a) Bluetooth configuration (b) Wireless LAN 10/26/2021 Sam_CN_UNIT- I 27

Wireless Networks (Cont’d) (a) Individual mobile computers (b) A flying LAN 10/26/2021 Sam_CN_UNIT- I 28

Internetworks l l l internet: a collection of interconnected networks Internet: specific worldwide internet Subnets: (WAN) collection of routers and communication lines (without hosts). Ex: telephone subnet Networks: combination of subnet and its hosts. Ex: telephone network = telephone subnets+ telephones internetwork: formed when distinct networks are connected together. Ex: connecting LAN and WAN 10/26/2021 Sam_CN_UNIT- I 29

Home Network Categories l l l Computers (desktop PC, PDA, shared peripherals Entertainment (TV, DVD, VCR, camera, stereo, MP 3) Telecomm (telephone, cell phone, intercom, fax) Appliances (microwave, fridge, clock, furnace etc. ) Telemetry (utility meter, burglar alarm etc. ) 10/26/2021 Sam_CN_UNIT- I 30

Network Software l l l Protocol Hierarchies Design Issues for the Layers Connection-Oriented and Connectionless Service Primitives The Relationship of Services to Protocols 10/26/2021 Sam_CN_UNIT- I 31

Protocol A protocol is an agreement that standardizes the way communication will be handled l It is a set of rules and conventions that governs exchange of data between two systems l A set of layers and protocols is called a network architecture l A list of protocols used by a certain system, one protocol per layer, is called a protocol stack l 10/26/2021 Sam_CN_UNIT- I 32

Protocol Hierarchies l l l Networks are organized as a stack of levels or layers We build each layer on the one below it Layers differ in number and function from one network to another Each layer hides underlying details from the one above it – sort of like a virtual machine Each layer talks to the ones above & below it 10/26/2021 Sam_CN_UNIT- I 33

Network Software Protocol Hierarchies Fig: Layers, protocols, and interfaces 10/26/2021 Sam_CN_UNIT- I 34

Data Transfer l No data is transferred directly from one machine to another on that layer – the layers can only talk to the ones above or below them on their host. l A message from layer 5 will have to travel to layer 1, move across the physical medium, and then back up to layer 5 on the different machine. l Layer 1 is the only layer able to move data from one machine to another, through the physical medium. 10/26/2021 Sam_CN_UNIT- I 35

Design Issues for the Layers l l l l A mechanism for identifying senders and receivers (naming and addressing) rules of transfer (simplex, half-duplex, fullduplex) error control (error correction and error detection) ordering and sequencing flow control, congestion control message or packet size (disassembling and reassembling) multiplexing and demultiplexing routing 10/26/2021 Sam_CN_UNIT- I 36

Connection-Oriented and Connectionless Services l Six different types of service 10/26/2021 Sam_CN_UNIT- I 37

Connection-Oriented and Connectionless Services Issue Initial Destination Packet Error Flow Option setup address sequence control negotiation only needed by by guaranteed during setup network layer Connection Oriented required Connectionless needed for by by not possible every packet guaranteed transport layer 10/26/2021 Sam_CN_UNIT- I Yes No 38

Service Primitives l 10/26/2021 Five service primitives for implementing a simple connection-oriented service Sam_CN_UNIT- I 39

The Relationship of Services to Protocols l A service defines what operations the layer is prepared to perform on behalf of its users, but it says nothing at all about how these operations are implemented. l A protocol, in contrast, is a set of rules governing the format and meaning of the frames, packets, or messages that are exchanged by the peer entities within a layer. Entities use protocols in order to implement their service definitions. 10/26/2021 Sam_CN_UNIT- I 40

Reference Models The OSI Reference Model l. In the late 1970 s, to promote the compatibility of network designs, the International Organization for Standardization (ISO) proposed an architecture model called the open systems interconnection references model (OSI model) services layer N PDUs (protocol data unit) layer N-1 layer N actual data flow on the lowest level 10/26/2021 Sam_CN_UNIT- I 41

The OSI Reference Model 10/26/2021 Sam_CN_UNIT- I 42

The OSI Reference Model 7 application 6 presentation 5 session 4 3 transport 2 1 data link 10/26/2021 network physical network services (email, file transfer) formatting, encryption, and compression setup and management of end-to-end conversation end-to-end delivery of messages end-to-end transmission of packets on one given link transmission of bits Sam_CN_UNIT- I 43

OSI Layers App X App Y Outgoing Packets Incoming Packets Data Application H Presentation H Session H Transport Network Data link Physical H H H Data Presentation Session Transport Network Data link Data Physical Path 10/26/2021 Sam_CN_UNIT- I 44

The Physical Layer Transmission of a raw bit stream forms the physical interface between devices l Makes sure that when one side sends a 1 bit , the other side receives it as a 1. l Covers all aspects for communication l Mechanical interface defines the connectors used, number of pins, their placement, size, material used. l Electrical interface defines the voltage/current levels of signals. l 10/26/2021 Sam_CN_UNIT- I 45

The Data Link Layer l l l l Data link layer attempts to make physical link reliable May divide upper layer packet into multiple frames Ensure that peer entity will recognize frame boundaries May introduce sequence numbers and acknowledgments Provides reliable transfer of information between two adjacent nodes Creates frames, or packets from bits and vice versa Provides frame-level error control Provides flow control 10/26/2021 Sam_CN_UNIT- I 46

The Network Layer l l l Network layer is designed to facilitate communication between systems across a communication network Implements network routing and message delivery through networks to the correct destination Congestion control can also be done at network layer Internetworking Internet protocol or IP is one example Responsible for routing decisions 10/26/2021 Sam_CN_UNIT- I 47

The Transport Layer l l l l l Provides reliable end-to-end communication May detect erroneous packets Reorders packets which arrive out-of-sequence. Ensures that there is no loss or duplication of packets May provide connection-less or connection-oriented type of service Provides for the connection management. Multiplexing and demultiplexing Packetization, flow control, etc. Examples: TCP and UDP Establishes and deletes connections across the network 10/26/2021 Sam_CN_UNIT- I 48

The Session Layer l l l Allows users on different computers to establish a session This layer requests for a logical connection to be established based on an end-user's request This layer provides services like dialogue discipline which can be full duplex or half duplex Session layer can also provide check pointing (or synchronization) mechanism If a failure occurs between checkpoints, all data can be retransmitted from the last checkpoint May perform synchronization and token management between several communicating applications 10/26/2021 Sam_CN_UNIT- I 49

The Presentation Layer l l Performs specific functions that are requested regularly by applications Presentation layer defines the data format to be exchanged between the programs. Manages abstract data structures, and converts them host-representation to network- representation and vice versa. Encryption 10/26/2021 Sam_CN_UNIT- I 50

The Application Layer Application layer protocols are application dependent l Implements communication between two applications of the same type - FTP - SMTP (email) etc. l 10/26/2021 Sam_CN_UNIT- I 51

What is TCP/IP ? l l l The name TCP/IP refers to a suite of data communication protocols Its name comes from two of the more important protocols in the suite: the Transmission Control Protocol (TCP) and the Internet Protocol (IP) The most common of all network protocol suites, is the ‘standard’ in modern networks, used for communication on the Internet Although designed for the Internet it is used to build LANs, WANs and MANs Most widely used protocol suite, used within Unix, Windows and Macintosh platforms 10/26/2021 Sam_CN_UNIT- I 52

The TCP/IP Reference model 10/26/2021 Sam_CN_UNIT- I 53

The TCP/IP Reference model Protocols and networks in the TCP/IP model initially 10/26/2021 Sam_CN_UNIT- I 54

The TCP/IP Protocol Suite Four-Layered Model Provides access to network services for the user and application programs Application Provides end-to-end transport Transport Path determination – routing Internet Access commn network LAN and WAN technologies 10/26/2021 Network Access (Host-to-network) Sam_CN_UNIT- I Protocols DNS FTP HTTP Telnet SMTP SNMP TFTP HTTP POP 3 TCP, UDP IP, ARP, ICMP, DHCP Ethernet, Token Ring, FDDI Frame Relay, ATM, ISDN 55

Host-to-Network Layer The TCP/IP model does not really say much about what happens here, except to point out that the host has to connect to the network so it can send IP packets to it l Access the communication network l 10/26/2021 Sam_CN_UNIT- I 56

Internet Layer Routes data between hosts l Connectionless l Every packet routed independently l Does not guarantee reliable or in-sequence delivery l 10/26/2021 Sam_CN_UNIT- I 57

Internet Layer (cont’d) The internet layer defines an official packet format for and protocol called Internet Protocol (IP) l It is the responsibility of the internet layer to get the IP packets to their destination l The TCP/IP internet layer is similar in functionality to the OSI network layer l 10/26/2021 Sam_CN_UNIT- I 58

Transport Layer The transport layer is intended to allow two machines to carry on a conversation, just like the OSI transport layer l There are two protocols defined for this: l TCP (Transmission Control Protocol) l reliable, connection-oriented l UDP (User Datagram Protocol) l unreliable, connectionless l 10/26/2021 Sam_CN_UNIT- I 59

Application Layer l This layer contains all of the higher-level protocols l telnet l FTP l SMTP l DNS l HTTP 10/26/2021 Sam_CN_UNIT- I 60

The differences between the TCP/IP and OSI models OSI model clearly defined the distinction between services, interfaces and protocols, where the TCP/IP model does not l This fits in nicely with OO programming concepts as the layer hide information l Protocols can easily be replaced in the OSI model, but not in the TCP/IP model l 10/26/2021 Sam_CN_UNIT- I 61

The Differences (cont’d) The OSI model has no biases for protocols, but the OSI model was overly general and did not help with the creation of new protocols l OSI supports connectionless and connection-oriented in the network layer, but only connection-oriented in the transport layer, providing no choice to the user l TCP/IP supports only connectionless in the network layer, but both in the transport layer, giving user a choice l 10/26/2021 Sam_CN_UNIT- I 62

A Critique of the OSI Model and Protocols Why OSI did not take over the world? l Bad timing l Bad technology l Bad implementations l Bad politics 10/26/2021 Sam_CN_UNIT- I 63

Bad Timing l The apocalypse of the two elephants 10/26/2021 Sam_CN_UNIT- I 64

A Critique of the TCP/IP Reference Model l l Service, interface, and protocol not distinguished Not a general model Host-to-network “layer” not really a layer No mention of physical and data link layers Minor protocols deeply entrenched, hard to replace 10/26/2021 Sam_CN_UNIT- I 65

Hybrid Model The hybrid reference model to be used in this book 10/26/2021 Sam_CN_UNIT- I 66

Example Networks l The Internet(ARPA NET) l Connection-Oriented Networks: X. 25, Frame Relay, and ATM l Ethernet l Novell Netware l Wireless LANs: 802: 11 10/26/2021 Sam_CN_UNIT- I 67

The ARPANET The original ARPANET design 10/26/2021 Sam_CN_UNIT- I 68

Internet Usage l l l Traditional applications (1970 – 1990) E-mail News Remote login File transfer 10/26/2021 Sam_CN_UNIT- I 69