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

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 Communication 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 only Blurring of boundaries in computing and communications  Microcomputer, Minicomputer, ….  Networks: LAN, MAN, WAN, …

5 Communication Main purpose of a communication system is: “Reliable exchange of data between two entities” 3 main areas:  Standards and Protocols  Networking Covers technology & architecture of communication networks Networks categorized into: LANs, MANs & WANs  Data Communications (Main Concern of COE 341) 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 Communication over a point-to-point link: A simplified model Generate Data Data to Signals Signals to Data Receive Data

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

8 This deceptive simplicity hides many important tasks! (See pages 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 = Tasks covered in some detail in this course Signal Data Data 1101… Noise, Distortion Interference Attenuation

9 Simplified Data Communications Model 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 (Multiplexing) (Ch 8) Speech,

10 Networking: Why do we need networks? Direct point-to-point communication is not always possible/practical/efficient:  Communicating entities can be too far apart for a single link  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)  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, e.g. telephone network, ISDN*  Packet switching, e.g.: Frame relay Cell relay (Asynchronous Transfer Mode (ATM)) Example:? * Integrated Services Digital Network

12 WAN Technologies: Circuit Switching 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

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

14 WAN Technologies, Contd: Packet Switching (store and forward) 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)

15 Packet Switching 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 Additional header info addressing and control (overhead) Useful user data (payload)

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

17 Evolution of Packet Switching Technology Older packet switching systems (X.25) had a 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

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

19 Newer forms of Packet Switching: 2. ATM Cell Relay 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.

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 possible by the shorter distances- small total attenuation  can afford using higher frequencies, e.g.: 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 standard)

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

22 Recent LAN Configurations (For further readings: see Part 4 of the textbook) Switched LAN  Switched Ethernet  ATM LAN  Fibre Channel Wireless LAN  Advantages: Mobility, Ease of installation  Example: WiFi (IEEE standard)

23 Metropolitan Area Networks (MAN) 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:  Stretching of LAN technology  Scaling down of WAN technology Now also going wireless!:  Example: WiMAX (IEEE standard)

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