COE 341 Data and Computer Communications 3 0

COE 341: Data and Computer Communications (3 -0 -3) Chapter 1: Data Communications & Networking: Overview

Acknowledgements Many figures, slides, and course notes were made available by: n Pearson Prentice-Hall (Publishers) q n Mc. Graw-Hill (Publishers) q n Data & Computer Communications, W. Stallings Data Communications & Networking, B. Forouzan Previous Course Offerings at COE, KFUPM by: q q q Dr. Marwan Abu-Amara Dr. Taha Landolsi Dr. Ashraf Mahmoud 2

Contents n Introduction q q n Communications Model q q n n Merging of computing and communications Integration of various types of data: Text, Pictures, Audio, Video Main blocks and functionality Communication Tasks Data Communication Networks q q q Wide Area Networks (WAN) n Circuit switching n Packet switching Local Area Networks (LAN) Metropolitan Area Networks (MAN) 3

Merging, Integration, and Blurring…. n Merging of computing and communications q n Integration of various types of information: Voice, Video, Text, Pictures, Data q n Computers communicate and communication devices (e. g. cell phones, routers) compute!… Before, they used to be handled by different dedicated networks, e. g. telephone network for voice only Blurring of boundaries in computing and communications q q Microcomputer, Minicomputer, …. Networks: LAN, MAN, WAN, … 4

n n Communicatio n purpose of a Main Hosts Routers, Switches communication system is: “Reliable exchange of data between two entities” 3 main areas: q q Standards and Protocols Networking n n q Covers technology & architecture of communication networks Networks categorized into: LANs, MANs & WANs Data Communications (Main Concern of COE 341) n n Reliable & efficient data communication over a link Covers signal transmission, transmission media, signal impairment, signal encoding, synchronization, error detection, data link control (error and flow), multiplexing 5

Communication over a point-to-point link: A simplified model Generate Data to Signals to Data Receive Data 6

Simplified Communications Model n Source (e. g. PC) q n Transmitter q n Carries signals, but introduces attenuation, noise, interference, etc. Receiver q n Converts data into transmittable signals (modulation, encoding) Transmission System (medium + equipment) q n Generates data to be transmitted Converts received signals into data (demodulation, decoding) Destination q Takes and uses incoming data Data 1101. . . Signal Noise, Distortion Interference Attenuation Data 1101… 7

This deceptive simplicity hides many important tasks! (See pages 11 -13 of the textbook for a good description) Interfacing Addressing Signal generation Routing Synchronization Recovery Exchange management: Message formatting Error detection and correction Security Error control Network management Flow control Transmission system utilization = Tasks covered in some detail in this course Data 1101. . . Signal Noise, Distortion Interference Attenuation Data 1101… 8

Simplified Data Communications Model Speech, n n n n Speech, Information (say ASCII chars) Data (bits) Signal (say 1 KHz signal) Encoding of data g(t) as signals s(t) (Ch. 5) Signal, s(t), should suit the transmission medium (Ch. 3 & 4) Transmission Impairments: attenuation, noise, distortion, etc. (Section 3. 3) Is received data, g’, identical to original data, g ? Error detection (Ch. 6) If not, Error correction at RX may help restore g Otherwise, request retransmission of message (Error control), Also flow control (Ch. 7) Better utilization of link capacity by multiplexing many channels 9 (Multiplexing) (Ch 8)

Networking: Why do we need networks? n Direct point-to-point communication is not always possible/practical/efficient: Communicating entities can be too far apart for a single link q A large set of communicating entities (e. g. telephones) would need impractically large number of connections (full connectivity for N nodes needs N (N – 1) / 2 links) q Not all links would be needed all the time! q n Solution is a communication network: q q q Wide Area Network (WAN) Metropolitan Area Network (MAN) Local Area Network (LAN) 10

Wide Area Networks (WAN) n n Large geographical area, e. g. the world Usually not owned by one organization Relies in part on common carrier circuits Alternative technologies q q Circuit switching, e. g. telephone network, ISDN* Packet switching, e. g. : n n n Frame relay Cell relay (Asynchronous Transfer Mode (ATM)) Example: ? * Integrated Services Digital Network 11

WAN Technologies: Circuit Switching n n n n Circuit switching was widely used for the public telephone networks for voice communication. Dedicated path is established before the call (session) starts and lasts for its duration Switching and transmission resources are committed for exclusive use of that call throughout its duration OK with telephony, as people keep talking till end of call Not the case with many computer data communication scenarios (bursty nature), e. g. Web browsing Advantage: Reliable, predictable performance – Delay, data rate, etc. Once connection is established, end devices appear as if connected directly through a dedicated link Disadvantage: Inefficient network utilization with computer type data communication 12

Simple Switched Computer Network End-to-end transmission medium is a network Switching Is Physical Switching Nodes Host Computers Link Network Computers (Switches) 13

WAN Technologies, Contd: Packet Switching (store and forward) n n n n No dedicated circuit assigned for the full session duration Data is split into small chunks (packets), each packet carries the destination address and a sequence number Packets may travel different routes to the destination arrive out of sequence, experience different delays, etc. Packets are passed from node to node from source to destination (possibly on multiple routes simultaneously) At destination, packets are assembled again to form the original message Used for terminal-to-computer and computer-to-computer data communications Possible problems for real-time traffic, e. g. telephony? : queuing delay, packet loss, etc. (Voice Over IP) 14

Packet Switching Useful user data (payload) Additional header info addressing and control (overhead) Each packet carries: - Destination address - Sequence number indicating packet position in original message Even if packets arrive out of sequence, they can still be re-assembled to reconstruct the message correctly at destination 15

Packet Switching (Store & Forward) Networks 1. Datagram (connectionless) Approach: 2. Virtual Circuit (connection) Approach: 16 2. No pre-planned route Frames follow one pre-planned route

Evolution of Packet Switching Technology n Older packet switching systems (X. 25) had a n n large overhead (redundancy) for handling errors This limited the useful user data rates to 64 kbps Now, modern transmission systems are more reliable ( fewer bit errors) And remaining few errors can be easily handled by higher layers at end systems Reducing data redundancy and processing at lower layers reduces the overhead, speeds up communication and increases useful (user) data rates 17

Newer forms of Packet Switching: 1. Frame Relay n n n Most overhead for error control is stripped off Variable-length packets (called frames) User data rates increased from 64 KB to 2 Mbps 18

Newer forms of Packet Switching: 2. ATM Cell Relay n n n Used on Asynchronous Transfer Mode (ATM) networks An evolution of frame relay Little overhead for error and flow control Fixed-length packets (called cells): 48 bytes data + a 5 -byte header Higher data rates than frame relay: 10 Mbps-Gbps Handles data for various types of information, e. g. speech, video, text, etc. 19

Local Area Networks (LANs Vs WANs) n Smaller geographical scope q A building or a small campus n Usually owned by the same organization that owns the attached devices (e. g. KFUPM) n Data rates are higher (this is made possible by the shorter distances- small total attenuation can afford using higher frequencies, e. g. : n n n Ethernet: 10 Mbps -10 Gbps over 100’s of meters Originally use a shared broadcast medium, e. g. coaxial cable But now some switched systems (originally WAN technology) are being introduced (Boundary Blurring!) Example: The Ethernet (IEEE 802. 3 standard) 20

Some LAN Topologies: (For further readings, see Part 4 of the textbook) Bus Ring Tree Star 21

Recent LAN Configurations (For further readings: see Part 4 of the textbook) n Switched LAN q q q n Switched Ethernet ATM LAN Fibre Channel Wireless LAN q q Advantages: Mobility, Ease of installation Example: Wi. Fi (IEEE 802. 11 standard) 22

Metropolitan Area Networks (MAN) n n n Requirements: Large capacity (data rate) at low cost and high efficiency to cover the geographical area of say a city Can be a private or public network Middle ground between LAN and WAN: q q n Stretching of LAN technology Scaling down of WAN technology Now also going wireless!: q Example: Wi. MAX (IEEE 802. 16 standard) 23

Example Residential Networking 1. Access Configuration: - Tel Line - ADSL Line - Cable Two ways of accessing the Internet Switched LAN Network 2. Through An access Network 24