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Computer networks CEN-330 ENG.Wisam oqilat Computer Science Department [email protected] Office hours :8:00-9:00,11:00-12:00,1:00-2:00 SUN.-TUS.-THU Course Objective The course is designed to introduce you to the world of computer networks, so that you could know the science being used in running this network Use this knowledge in your professional field The course covers concepts and useful tools for design and performance analysis of data communication networks Reading Text book: Data Communications and Networking, 4/e B.A. Forouzan, McGraw-Hill, 2003, ISBN 0-07-292354-7. Reference books: Computer Networking, a top-down approach featuring the Internet (3rd edition), J.K.Kurose, K.W.Ross, Addison-Wesley, 2005, ISBN 0-321-26976-4. Computer Networks, A Systems Approach L. Peterson & Davie Grading Policy lab Quizzes First Sessional Second Sessional Final Exam : : : : : 20 % 10% 15% 15% 40% Grading Policy is Tentative Data Communications Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. 24/12/37 CEN 330 by ENG.WISAM 5 Five Components of Data Communication 24/12/37 1. Message 2. Sender 3. Receiver 4. Medium 5. Protocol CEN 330 by ENG.WISAM 6 What’s a protocol? A protocol is a set of rules that governs data communications Key elements of a protocol are Syntax Semantics Timing 24/12/37 CEN 330 by ENG.WISAM 7 Direction of data flow Simplex Half Duplex Full Duplex 24/12/37 CEN 330 by ENG.WISAM 8 Type of connections Point-to-point Point-to-multipoint One-to-one communication Unicasting Communication channel shared among nodes One-to-many Broadcasting Multicasting Multipoint-to-point 24/12/37 Many-to-one CEN 330 by ENG.WISAM 9 Network topologies Topology defines the way hosts are connected to the network 24/12/37 CEN 330 by ENG.WISAM 10 Network topology issues a goal of any topology 1. high throughput (bandwidth) 2. low latency 24/12/37 CEN 330 by ENG.WISAM 11 Terminology The throughput or bandwidth of a channel is the number of bits it can transfer per second The latency or delay of a channel is the time that elapses between sending information and the earliest possible reception of it 24/12/37 CEN 330 by ENG.WISAM 12 Categories of Topology 24/12/37 CEN 330 by ENG.WISAM 13 Mostly used network topologies bus mesh ring star 24/12/37 CEN 330 by ENG.WISAM 14 A hybrid topology: a star backbone with three bus networks 24/12/37 CEN 330 by ENG.WISAM 15 Categories of Network Generally there are three categories of network Local Area network (LAN) Metropolitan Area Network (MAN) Wide Area Network (WAN) Category into which a network falls is determined by its size 24/12/37 CEN 330 by ENG.WISAM 16 Categories of Network(2) Local Area Network (LAN) Wide Area Network (WAN) A local area network (LAN) is usually privately owned and links the devices in a single office, building, or campus A wide area network (WAN) provides long-distance transmission of data over large geographic area that may comprise a country, continent or world wide. Metropolitan Area Network (MAN) 24/12/37 A metropolitan area network MAN )is a network with a size between a LAN and a WAN. Usually it is spreaded over a city or a part of a city CEN 330 by ENG.WISAM 17 Protocol protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt a human protocol and a computer network protocol: Hi time TCP connection req. Hi TCP connection reply. Got the time? Get http://gaia.cs.umass.edu/index.htm 2:00 24/12/37 <file> CEN 330 by ENG.WISAM 18 Layered Tasks An example from the everyday life Hierarchy? Services 24/12/37 CEN 330 by ENG.WISAM 19 Why layered communication? To reduce complexity of communication task by splitting it into several layered small tasks Functionality of the layers can be changed as long as the service provided to the layer above stays unchanged makes easier maintenance & updating Each layer has its own task Each layer has its own protocol 24/12/37 CEN 330 by ENG.WISAM 20 Reference Models OSI reference model TCP/IP 24/12/37 CEN 330 by ENG.WISAM 21 OSI Reference model 1. 2. 3. 4. Open System Interconnection 7 layers Create a layer when different abstraction is needed Each layer performs a well define function Functions of the layers chosen taking internationally standardized protocols Number of layers – large enough to avoid complexity 24/12/37 CEN 330 by ENG.WISAM 22 Seven layers of the OSI model 24/12/37 CEN 330 by ENG.WISAM 23 Exchange using OSI Model 24/12/37 CEN 330 by ENG.WISAM 24 The interaction between layers in the OSI model 24/12/37 CEN 330 by ENG.WISAM 25 Issues, to be resolved by the layers Larger bandwidth at lower cost Error correction Flow control Addressing Multiplexing Naming Congestion control Mobility Routing Fragmentation Security .... 24/12/37 CEN 330 by ENG.WISAM 26 OSI Layers 24/12/37 CEN 330 by ENG.WISAM 27 Physical layer physical connection Transporting bits from one end node to the next - type of the transmission media (twisted-pair, coax, optical fiber, air) - bit representation (voltage levels of logical values) - data rate (speed) - synchronization of bits (time synchronization) 24/12/37 CEN 330 by ENG.WISAM 28 Note The physical layer is responsible for movements of individual bits from one hop (node) to the next. 24/12/37 CEN 330 by ENG.WISAM 29 Data Link layer logical connection Transporting frames from one end node to the next one - framing - physical addressing - flow control - error control - access control 24/12/37 CEN 330 by ENG.WISAM 30 Data Link layer - hop-to-hop delivery- 24/12/37 CEN 330 by ENG.WISAM 31 Data Link layer - example- 24/12/37 CEN 330 by ENG.WISAM 32 Note The data link layer is responsible for moving frames from one hop (node) to the next. 24/12/37 CEN 330 by ENG.WISAM 33 Network layer Not a message End-to-End packet delivery Needed when 2 devices are attached to different networks What is the network definition here? Main duties: 1. 2. 3. 24/12/37 From the original source to a destination Logical addressing Routing Congestion control and QoS CEN 330 by ENG.WISAM 34 Source to destination delivery Data Link Network layer 24/12/37 CEN 330 by ENG.WISAM 35 Network layer - example - Network layer addresses Data Link layer addresses 24/12/37 CEN 330 by ENG.WISAM 36 Note The network layer is responsible for the delivery of individual packets from the source host to the destination host. 24/12/37 CEN 330 by ENG.WISAM 37 Transport layer Process-to-Process delivery of the entire message From the original source to a destination Needed when several processes (running programs) active at the same time Main tasks: 24/12/37 Port addressing Segmentation and reassembly Congestion control Flow control Error control CEN 330 by ENG.WISAM 38 Transport Layer 24/12/37 CEN 330 by ENG.WISAM 39 Transport layer -an example of a reliable delivery - 24/12/37 CEN 330 by ENG.WISAM 40 Note The transport layer is responsible for the delivery of a message from one process to another. 24/12/37 CEN 330 by ENG.WISAM 41 Note The session layer is responsible for dialog control and synchronization. 24/12/37 CEN 330 by ENG.WISAM 42 Note The presentation layer is responsible for translation, compression, and encryption. 24/12/37 CEN 330 by ENG.WISAM 43 Application layer Enables user to access the network Provides services to a user 24/12/37 E-mail Remote file access and transfer (Telnet, FTP) Access to WWW (HTTP) CEN 330 by ENG.WISAM 44 Note The application layer is responsible for providing services to the user. 24/12/37 CEN 330 by ENG.WISAM 45 OSI Reference Model A convenient aid for remembering the OSI layer names is to use the first letter of each word in the phrase: All People Seem To Need Data Processing 24/12/37 CEN 330 by ENG.WISAM 46 Summary of layers and protocols Low-level protocols define the electrical and physical standards to be observed, bit- and byte-ordering and the transmission and error detection and correction of the bit stream High-level protocols deal with the data formatting, including the syntax of messages, the terminal to computer dialogue, character sets, sequencing of messages 24/12/37 CEN 330 by ENG.WISAM 47 TCP/IP Protocol 24/12/37 CEN 330 by ENG.WISAM 48 TCP/IP Vs OSI Model 24/12/37 CEN 330 by ENG.WISAM 49 Four Level of Addresses 24/12/37 CEN 330 by ENG.WISAM 50 Relationship of Layers & Addresses in TCP/IP 24/12/37 CEN 330 by ENG.WISAM 51 Note The physical addresses will change from hop to hop, but the logical addresses usually remain the same. A port address is a 16 bit address represented by one decimal number 24/12/37 CEN 330 by ENG.WISAM 52 Ethernet Addresses The least significant bit of the first byte defines the type of address. If the bit is 0, the address is unicast; otherwise, it is multicast. The broadcast destination address is a special case of the multicast address in which all bits are 1s. Data Communication & Networks, Fall 2009 53 Example Define the type of the following destination addresses: a. 4A:30:10:21:10:1A b. 47:20:1B:2E:08:EE c. FF:FF:FF:FF:FF:FF Solution To find the type of the address, we need to look at the second hexadecimal digit from the left. If it is even, the address is unicast. If it is odd, the address is multicast. If all digits are F’s, the address is broadcast. Therefore, we have the following: a. This is a unicast address because A in binary is 1010. b. This is a multicast address because 7 in binary is 0111. c. This is a broadcast address because all digits are F’s. Data Communication & Networks, Fall 2009 54 Example Show how the address 47:20:1B:2E:08:EE is sent out on line. Solution The address is sent left-to-right, byte by byte; for each byte, it is sent right-to-left, bit by bit, as shown below: Data Communication & Networks, Fall 2009 55 QUESTIONS 24/12/37 CEN 330 by ENG.WISAM 56