Chapter 1: Data Communications & Networking: Overview

1. COE 341: Data and Computer Communications (3-0-3) Term 062 Chapter 1: Data Communications & Networking: Overview

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

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

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

5. Routers, Switches Communication Hosts • Main purpose of a communication system is: “Reliable exchange of data between two parties” • 3 main areas: • Networking • Covers technology & architecture of communication networks • Networks divided into LANs, MANs & WANs • Standards and Protocols • Data Communications (Main Concern of COE341) • 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

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

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

8. Noise, Distortion Interference Attenuation Signal Data 1101... Data 1101… Behind this deceptive simplicity hide many important tasks!(Pages 11-13 of the textbook for a good description) = Task covered in some detail in this course

9. Simplified Data Communications Model Speech, Speech, • Information Data 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 info, m’, identical to original input info, m ? Error detection(Ch. 6) • If not, Error correction may help restore m(Ch. 6) (Not covered) • Otherwise, request retransmission of message (Error control), Also flow control(Ch. 7) • Better utilization of link capacity by multiplexing many channels (Multiplexing) (Ch 8)

10. NetworkingWhy do we need networks? • Point to point communication not usually practical • Devices can be too far apart for a single link • A large set of devices (e.g. telephones) would need impractically large number of connections (full connectivity for N nodes needs N (N – 1) / 2 links) • Not all links would be needed all the time! • Solution is a communication network: • Wide Area Network (WAN) • Metropolitan Area Network (MAN) • Local Area Network (LAN)

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

12. WAN Technologies: Circuit Switching • Circuit switching is used in the public telephone network for voice communication. • Dedicated path is established for the duration of the call (session) • Switching and transmission resources are committed for exclusive use of the call throughout its duration • OK with telephony, as people keep talking till end of call • Not the case with many computer data situations (bursty) • Advantage: Reliable, predictable performance – Once connection is established, devices appear as if connected directly through a dedicated link • Disadvantage: Inefficient utilization with computer type data communication

13. Simple Switched Network Transmission medium is a network Addressing Switching Nodes Link (Computers) Routing Host

14. WAN Technologies: Packet Switching • No dedicated circuit assigned for the full session duration • Data is split into small chunks (packets), each packet carries destination address and sequence number • Packets may arrive out of sequence via different routes • Packets are passed from node to node from source to destination on (possibly 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 telephony? (Voice Over IP)

15. Packet Switching Even if packets arrive out of sequence, they can still be re-assembled to reconstruct the message correctly at destination • Each packet carries: • Destination address • Sequence number indicating its position • in original message

16. Packet Switching (Store & Forward) Networks • DatagramApproach: • No pre-planned route 2. Virtual Circuit Approach: Frames follow one pre-planned route

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

18. Newer forms of Packet Switching:1. Frame Relay • Most overhead for error control is stripped out • Variable-length packets (called frames) • User data rates up to 2 Mbps

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

20. Local Area Networks (LANs Vs WANs) • Smaller geographical scope • A building or a small campus • Usually owned by the same organization that owns the attached devices (e.g. KFUPM) • Data rates are higher (this is made easier by the shorter distances- small total attenuation, can afford using higher frequencies:10 Mbps -10 Gbps over 100’s of meters • Now some switched systems and ATM are being introduced (Boundary Blurring) • The Ethernet: IEEE 802.3

21. Some LAN Topologies:(For further readings: Part 4 of the textbook) Bus Ring Tree Star or Hub

22. Recent LAN Configurations(For further readings: see Part 4 of the textbook) • Switched LAN • Switched Ethernet May use single or multiple switches • ATM LAN • Fibre Channel • Wireless LAN • Advantages: Mobility, Ease of installation • WiFi (IEEE 802.11)

23. Metropolitan Area Networks (MAN) • Requirements: Large capacity (data rate) at low cost and high efficiency to cover the area of say a city • Can be a private or public network • Middle ground between LAN and WAN: • Stretching of LAN technology • Scaling down of WAN technology • Now also going wireless!: WiMAX (IEEE 802.16)

24. Example NetworkingConfiguration • - Tel Line • - ADSL Line • Cable LAN Network