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1. Lecture#01
Computer Communications
& Networks CS-576

2. Text Books
 Data and Computer Communications,
7th Edition, Prentice Hall, 2004
by William Stallings
 Data Communication and Networking,
Fourth Edition, McGraw-Hill, 2004
by Behrouz A. Forouzan

3. Data Communication
 Data Communication is the exchange of data(in the
form of 0,s and 1, s) between two
devices(Computers)via some form of Transmission
medium .

4. Local And Remote Data 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.

5. 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

6. Effectiveness of data communication
depends on
 Delivery
 System must deliver data to correct destination
 Accuracy
 Data delivered accurately.
 Timeliness
 Data delivered in timely manner without delay

7. Components of Data Communication
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

8.  Medium
 Physical path 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.

9. Data Communication Model Diagram
(a) Block diagram

10. 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)


11. Data Flow
 Communication between 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

12.  Half-duplex
 Each station 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

13.  Full-Duplex
 Both stations 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

14. Network
 A NETWORK is 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)

15. Distributed Processing
 Instead of 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

16. Network Criteria
 A network 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

17. 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

18. Protocols and standards
 There are three key elements
 Syntax
 Semantics
 Timming

19. Standard Organisations
 IEEE
 ITU-T
 ACM
 ANSI
 ISO
 EIA