1 Data Communications CS 1302 Computer Networks Unit 1 Topics 1,2,3

2 Overview

3 Data Communications Data – facts, concepts, and instructions Data – Information presented in whatever form is agreed upon by the parties creating and using the data Represented by binary information units (in the form of 0s and 1s) Data Communications – exchange of data between two devices via some form of transmission medium such as a wire cable

4 Effectiveness of Data Communications Effectiveness of a data communications system depends on three fundamental characteristics  Delivery : The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device or user  Accuracy: The system must deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable  Timeliness: The system must deliver data in a timely manner. Data delivered late are useless. Delivering the data in the same order that they are produced and without significant delay (real time transmission)

5 Data Communication Components Data Representation Direction of Data Flow

6 Five components of data communication Message: Information to be communicated. Consist of text, numbers, pictures, sound or video - combination

7 Five components of data communication Sender: device that sends the data message- may be computer, workstation. telephone handset, video camera and etc.

8 Five components of data communication Receiver: the device that receives the message. Can be computer, work station, telephone handset, television and so on.

9 Five components of data communication Medium: Physical path by which a message travels from sender to receiver – twisted pair wire, coaxial cable, fibre optic cable or radio waves

10 Five components of data communication Protocol: Set of rules that governs data communication. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating

11 Data Communication Data Representation Direction of Data Flow

12 Data Representation (1) Information Today comes in different forms such as text, numbers, images, audio and video Text: Represented as a bit pattern, a sequence of bits 0s or 1s. Different codes are used  ASCII (7 bits per symbol)  Extended ASCII (8 bits per symbol)  Unicode (16 bits – supports different languages)  ISO (32 bits)

13 Data Representation (2) Numbers  Converted to a binary number – to simplify the mathematical operations Images  Represented by bit patterns  Each pixel is assigned a bit pattern  Black and White Image – 1 bit per pixel  Gray scale images – depends on number of levels in gray scale  Colour images: Each pixel has 3 bit patterns (RGB) Audio / Video  Converted in to Analog/Digital

14 Data Communication Direction of Data Flow

15 Simplex Simplex – unidirectional; one transmits, other receives

16 Half-duplex Half-duplex – each can transmit/receive; communication must alternate

17 Full-duplex Full-duplex – both can transmit/receive simultaneously

18 Networks Network Criteria Physical Structures Categories of Networks

19 Networks Set of devices (nodes) connected by media Distributed processing Advantages

20 Applications (2) Peer-Peer model:  No fixed clients or servers  Each host can act as both client & server Examples: Napster, Gnutella, KaZaA

21 Applications (3) WWW Instant Messaging (Internet chat, text messaging on cellular phones) Peer-to-Peer Internet Phone Video-on-demand Distributed Games Remote Login (Telnet) File Transfer

22 Network Criteria Performance – can be measured by transit time and response time. Affected by number of users, type of medium, connected HW/SW Reliability – measured by frequency of failure, recovery time, robustness in a catastrophe Security – protection from unauthorized access, viruses / worms

23 Type of Connections Line Configuration

24 Line Configuration The way two or more communication devices attach to a link Link – Physical communication pathway that transfer data from one device to another Two possible line configurations  Point-to-point  Multipoint

25 Point-to-point connection

26 Multipoint connection

27 Topology Physical or logical arrangement Topology of a network is the geometric representation of the relationship of all the links and linking devices to one another 4 basic types: mesh, star, bus, ring May often see hybrid

28 Categories of topology

29 Mesh Topology Dedicated point-to-point links to every other device n(n-1)/2 links an each device will have n-1 I/O ports Advantages  Dedicated links – no traffic problems  Robust  Privacy/Security  Easy fault identification and isolation Disadvantages  more amount of cabling and I/O ports requirement  Installation and reconnection is difficult  Expensive

30 Star Topology Dedicated point-to-point links to central controller (hub) Controller acts as exchange Advantages  less expensive  robustness Disadvantages  More cabling requirement than ring and bus topologies

31 Bus Topology Multipoint configuration One cable acts as a backbone to link all devices Advantages : Ease of installation, less cabling Disadvantages : Difficult reconnection and fault isolation, a fault/break in the bus cable stops all transmission

32 Ring Topology Dedicated point-to-point configuration to neighbors Signal is passed from device to device until it reaches destination Each device functions as a repeater Advantages : easy to install and reconfigure Disadvantages :limited ring length and no: of devices; break in a ring can disable entire network

33 Categories of Networks Based on size, ownership, distance covered, and physical architecture  Local Area Network (LAN) – smaller geographical area  Metropolitan Area Network (MAN) – network extended over an entire city  Wide Area Network (WAN) – large geographical area

34 Categories of networks

35 LAN Privately owned and links the devices in a single office, building or campus

36 LAN (Continued)

37 MAN Designed to extend over an entire city – May be a single network such as cable television network – may be a means of connecting a number of LANS into a larger network

38 Metropolitan Area Network (MAN) home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes A Cable TV Network is an example of a MAN

39 WAN Provides long distance transmission of data, voice, image and video information over large geographic areas – a country/continent/world

40 Protocols and Standards Protocols Standards

41 Protocols and Standards Protocols  Set of rules that governs data communications  Defines what is communicated, how it is communicated, and when it is communicated  Key elements Syntax : Structure/ format of data –order in which it is presented Semantics : meaning of each section of bits- how pattern to be interpreted – What action to be taken Timing: When data to be sent and how fast they can be sent

42 Protocols and Standards Standards  Essential in creating and maintaining an open and competitive market for equipment manufacturers and in guaranteeing national and international interoperability of data and telecommunications technology and processes  De facto: Standards that have not been approved by an organized body but have been adopted as standards through widespread use  De jure: legislated by an officially recognized body

43 Protocols and Standards Standards Organizations  International organization for Standardization (ISO)  International Telecommunication Union – Telecommunication Standards Sector (ITU-T)  American National Standards Institute (ANSI)  Institute of Electrical and Electronics Engineers (IEEE)  Electronic Industries Assoctiation (EIA)

44 Protocols and Standards Regulatory Agencies  Federal Communication Commission (FCC) Internet Standards  Internet Draft  Request for Comment (RFC)