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

2. 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. 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. 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. 5 Communication 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 Hosts Routers, Switches

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

7. 7 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 Signal Data 1101... Data 1101… Noise, Distortion Interference Attenuation

8. 8 Behind this deceptive simplicity hide many important tasks! (Pages 11-13 of the textbook for a good description) InterfacingAddressing Signal generationRouting SynchronizationRecovery Exchange management:Message formatting Error detection and correctionSecurity Error controlNetwork management Flow controlTransmission system utilization = Task covered in some detail in this course Signal Data 1101... Data 1101… Noise, Distortion Interference Attenuation

9. 9 Simplified Data Communications Model 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) Speech,

10. 10 Networking Why 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. 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. 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. 13 Simple Switched Network Switching Nodes Link (Computers) Routing Addressing Transmission medium is a network Host

14. 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. 15 Packet Switching Each packet carries: - Destination address - Sequence number indicating its position in original message Even if packets arrive out of sequence, they can still be re-assembled to reconstruct the message correctly at destination

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

17. 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. 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. 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. 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. 21 Some LAN Topologies: (For further readings: Part 4 of the textbook) Star or Hub Ring Bus Tree

22. 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. 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. 24 Example Networking Configuration - Tel Line - ADSL Line - Cable LAN Network