Lecture 01

Lecture 01

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  Lecture#01 Computer Communications & NetworksCS-576
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  Text Books  Dataand Computer Communications, 7th Edition, Prentice Hall, 2004 by William Stallings  Data Communication and Networking, Fourth Edition, McGraw-Hill, 2004 by Behrouz A. Forouzan
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  Data Communication  DataCommunication is the exchange of data(in the form of 0,s and 1, s) between two devices(Computers)via some form of Transmission medium .
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  Local And RemoteData Communication  LOCAL :Data communication is considered to be local if the communicating devices are present in the same building or a similarly restricted geographical area.  REMOTE: Data Communication is considered remote, if the devices are farther apart.
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  Data Communication System For Data Communication to occur, the communicating devices must be a part of a communication system made up of Combination of hardware and software
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  Effectiveness of datacommunication depends on  Delivery  System must deliver data to correct destination  Accuracy  Data delivered accurately.  Timeliness  Data delivered in timely manner without delay
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  Components of DataCommunication System/Data Communication Model  Any system is made up of more than one component. Similarly, a data communication system is made up of 5 components as shown in the fig:  Message  Information or Data to be communicated  Can be text, numbers, video or any combination of these  Sender  Device that sends the data message  can be a computer or video camera etc  Receiver  Device that receives the message can be a computer etc
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   Medium  Physicalpath that a message uses to travel from the Sender to the receiver.  Can be a Copper Cable (Telephone), Coaxial Cable (Cable TV), Fiber optic cable, Laser or radio waves(wireless medium)  Protocol  Set of Rules Governing Communication. Represents an Agreement between communication devices  Without Protocol, two devices may be connected but they will not communicating.
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  Data Communication ModelDiagram (a) Block diagram
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  Data Representation  Text Represented as a bit pattern(Sequence of 0,s and 1,s)  Unicode:32bitpattern to represent symbols used in any language in the world.  ASCII:7bitpattern  Extended ASCII:8bitpattern  Numbers  Numbers is directly converted to binary Numbers  Images  represented by matrix of pixels ,where each pixel is a dot  An image made of white and Black dots(e.g ,a chessboard) a 1-bit pattern is enough to represent a pixel  One method to represent color image is RGB(Red +Green +Blue)  Another method to represent color image is YCM(Yellow+cyan+magenta) 
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  Data Flow  Communicationbetween two devices can be  Simplex  Half- Duplex  Full- Duplex  Simplex  communication is unidirectional. (one-way-street). Only one of the two devices on a link can transmit; the other can only receive, As Keyboard and monitors
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   Half-duplex  Eachstation can both transmit and receive , but not at the same time. When one device is sending the other can receive and vice versa. one-lane road with two direction) As Walkie-talkie
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   Full-Duplex  Bothstations can transmit and receive simultaneously. ( telephone network)  Signals going in either direction share the capacity of the link in two ways:  Either the link must contain two physically separate transmission paths one for sending and other for receiving.  Capacity of the channel is divided between signals traveling in both direction
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  Network  A NETWORKis a set of devices (Nodes) connected by Communication Links.  Node Can be a Computer, Printer or any other device capable of sending or receiving  Nodes attached to media through NIC (network interface card)
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  Distributed Processing  Insteadof a single large machine being responsible for all aspects of a process , each separate computer handles a subset of the task  Advantages  Security  Distributed Database  Faster Problem solving
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  Network Criteria  Anetwork must be able to meet certain number of criteria .Most Important are Performance, reliability and Security  Performance-depends on  Number of user  Type of transmission media,  Hardware  Software  Reliability-measured by  Frequency of failure  The time it takes to recover from failure  Catastrophe  Security  Protection from unauthorized access and viruses
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  TYPE OF CONNECTION Point to point  A dedicated link is provided between two devices  The entire capacity of the link is reserved for transmission between these two devices.  Most of them uses an actual length of wire or cable to connect the two ends but other options ,such as microwave satellite are possible  Multipoint  More than two devices share a single line.  The capacity is shared either spatially or temporally.  Spatially: Several devices can use link simultaneously  Temporally: Users take turns , it is a timeshared
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  Protocols and standards There are three key elements  Syntax  Semantics  Timming
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  Standard Organisations  IEEE ITU-T  ACM  ANSI  ISO  EIA