ch#1 (commication) notes

8/20/2019 Ch#1 (Commication) Notes

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Chapter # 1

Fundamental Characteristics of data communication

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. In the case

of video and audio, timely delivery means delivering data as they are produced, in the same

order that they are produced, and without signicant delay. This kind of delivery is called real-

time transmission.

Jitter:-

itter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of

audio or video packets. !or e"ample, let us assume that video packets are sent every #D ms. If

some of the packets arrive with #D-ms delay and others with $D-ms delay, an uneven %uality

in the video is the result.

Components of Data Communication

A data communications system has ve components

Messae:-

The message is the information &data' to be communicated. (opular forms of information

include te"t, numbers, pictures, audio, and video.

!ender:-

The sender is the device that sends the data message. It can be a computer, workstation,

telephone handset, video camera, and so on.

"eceiver:-

The receiver is the device that receives the message. It can be a computer, workstation,

telephone handset, television, and so on.

Transmission medium:-

The transmission medium is the physical path by which a message travels from sender to

receiver. )ome e"amples of transmission media include twisted-pair wire, coa"ial cable, ber-

optic cable, and radio waves.

rotocol:-

* protocol is a set of rules that govern data communications. It represents an agreement

between the communicating devices. +ithout a protocol, two devices may be connected but

not communicating, ust as a person speaking !rench cannot be understood by a person who

speaks only apanese.


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Data Flo$

Communication %et$een t$o devices can %e simple&' half-duple&' or full-duple&(

!imple&:-

In simple" mode, the communication is unidirectional, as on a one-way street. nly one of the

two devices on a link can transmit the other can only receive./eyboards and traditionalmonitors are e"amples of simple" devices. The keyboard can only introduce input the monitor

can only accept output. The simple" mode can use the entire capacity of the channel to send

data in one direction.

)alf-Duple&:-

In half-duple" mode, each station can both transmit and receive, but not at the same

time.+hen one device is sending, the other can only receive, and vice versa. The half-duple"

mode is like a one-lane road with tra0c allowed in both directions. +hen cars are traveling in

one direction, cars going the other way must wait. In a half-duple" transmission, the entire

capacity of a channel is taken over by whichever of the two devices is transmitting at the time.

+alkie-talkies and 12 &citi3ens band' radios are both half-duple" systems. The half-duple"

mode is used in cases where there is no need for communication in both directions at the

same time the entire capacity of the channel can be utili3ed for each direction.

Full-Duple&:-

In full-duple" m.,lle &als4 called duple"', both stations can transmit and receive

simultaneously.The full-duple" mode is like a two-way street with tra0c 5owing in both

directions at the same time. In full-duple" mode, signals going in one direction share thecapacity of the link: with signals going in the other direction.This sharing can occur in two

ways: 6ither the link must contain two physically separate transmission paths, one for sending

and the other for receiving or the capacity of the channel is divided between signals traveling

in both directions. ne common e"ample of full-duple" communication is the telephone

network. +hen two people are communicating by a telephone line, both can talk and listen at

the same time. The full-duple" mode is used when communication in both directions is

re%uired all the time. The capacity of the channel, however, must be divided between the two

directions.


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Type of Connection

* network is two or more devices connected through links. * link is a communications pathway

that transfers data from one device to another. !or communication to occur, two devices must

be connected in some way to the same link at the same time. There are two possible types of

connections: point-to-point and multipoint.

oint-to-oint:-

* point-to-point connection provides a dedicated link between two devices. The entire capacity

of the link is reserved for transmission between those two devices. 7ost point-to-point

connections use an actual length of wire or cable to connect the two ends, but other options,such as microwave or satellite links, are also possible. +hen you change television channels

by infrared remote control, you are establishing a point-to-point connection between the

remote control and the television8s control system.

Multipoint:-

* multipoint &also called multidrop' connection is one in which more than two specic devices

share a single link. In a multipoint environment, the capacity of the channel is shared, either

spatially or temporally. If several devices can use the link simultaneously, it is a spatially

shared connection. If users must take turns, it is a timeshared connection.

Types of *et$or+

Depending upon the geographical area covered by a network, it is classied as:

9 ocal *rea ;etwork &*;'

9 7etropolitan *rea ;etwork &7*;'

9 +ide *rea ;etwork &+*;'

,A*

< * *; is a network that is used for communicating among computer devices, usually within

an o0ce building or home.

< *;=s enable the sharing of resources such as les or hardware devices that may be needed

by multiple users.

< Is limited in si3e, typically spanning a few hundred meters, and no more than a mile

< Is fast, with speeds from >? 7bps to >? @bps

< Ae%uires little wiring, typically a single cable connecting to each device

< Bas lower cost compared to 7*;=s or +*;=s

< *;=s can be either wired or wireless. Twisted pair, coa" or bre optic cable can be used in

wired *;=s.


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< 6very *; uses a protocol 9 a set of rules that governs how packets are congured and

transmitted.

< ;odes in a *; are linked together with a certain topology. These topologies include:

9 2us

9 Aing

9 )tar< *;s are capable of very high transmission rates &>??s 7bCs to @ bCs'.

Disadvantaes of ,A*

< 6"pensive To Install

< Ae%uires *dministrative Time

< !ile )erver 7ay !ail

< 1ables 7ay 2reak

Advantaes of ,A*

< )peed

< 1ost

< )ecurity

< 6-mail

< Aesource )haring

MA*Metropolitan Area *et$or+.

< * metropolitan area network &7*;' is a large computer network that usually spans a city or

a large campus.

< * 7*; is optimi3ed for a larger geographical area than a *;, ranging from several blocks

of

buildings to entire cities.

< * 7*; might be owned and operated by a single organi3ation, but it usually will be used by

many individuals and organi3ations.

< * 7*; often acts as a high speed network to allow sharing of regional resources.

< * 7*; typically covers an area of between and ? km diameter.

< 6"amples of 7*;: Telephone company network that provides a high speed D) to

customers and cable TE network.

/A* /ide Area *et$or+.

< +*; covers a large geographic area such as country, continent or even whole of the world.

< * +*; is two or more *;s connected together. The *;s can be many miles apart.


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< To cover great distances, +*;s may transmit data over leased high-speed phone lines or

wireless links such as satellites.

< 7ultiple *;s can be connected together using devices such as bridges, routers, or

gateways, which enable them to share data.

< The world8s most popular +*; is the Internet.

*et$or+ Topoloies

< ;etwork topologies describe the ways in which the elements of a network are mapped. They

describe the physical and logical arrangement of the network nodes.

< The physical topology of a network refers to the conguration of cables, computers, and

other peripherals

Di0erent Types of Topoloies< 2us Topology

< )tar Topology

< Aing Topology

< 7esh Topology

< Tree Topology

< Bybrid Topology

us Topoloy< *ll the nodes &le server, workstations, and peripherals' on a bus topology are connected by

one single cable.

< * bus topology consists of a main run of cable with a terminator at each end. *ll nodes &le

server, workstations, and peripherals' are connected to the linear cable.

< (opular on *;s because they are ine"pensive and easy to install.

Advantaes of us Topoloy

< It is 1heap, easy to handle and implement.

< Ae%uire less cable

< It is best suited for small networks.

Disadvantaes of us Topoloy

< The cable length is limited. This limits the number of stations that can be connected.

< This network topology can perform well only for a limited number of nodes.

"in Topoloy

< In a ring network, every device has e"actly two neighbours for communication purposes.


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< *ll messages travel through a ring in the same direction.

< * failure in any cable or device breaks the loop and can take down the entire network.

< To implement a ring network we use the Token Aing technology

< * token, or small data packet, is continuously passed around the network. +hen a device

needs to transmit, it reserves the token for the ne"t trip around, then attaches its data packet

to it.

Advantae of "in Topoloy

< Eery orderly network where every device has access to the token and the opportunity to

transmit.

< 6asier to 7ange than a 2us ;etwork

< @ood 1ommunication over long distances

< Bandles high volume of tra0c

Disadvantaes of "in Topoloy

< The failure of a single node of the network can cause the entire network to fail.

< The movement or changes made to network nodes aFects the performance of the entire

network.

!tar Topoloy

< In a star network, each node &le server, workstations, and peripherals' is connected to a

central device called a hub.

< The hub takes a signal that comes from any node and passes it along to all the other nodes

in the network.

< Data on a star network passes through the hub, switch, or concentrator before continuing to

its destination.

< The hub, switch, or concentrator manages and controls all functions of the network.

< The star topology reduces the chance of network failure by connecting all of the systems to a

central node.

Advantaes of !tar Topoloy

< 6asy to manage

< 6asy to locate problems &cableCworkstations'

< 6asier to e"pand than a bus or ring topology.

< 6asy to install and wire.

< 6asy to detect faults and to remove parts.

Disadvantaes of !tar Topoloy

< Ae%uires more cable length than a linear topology.


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< If the hub or concentrator fails, nodes attached are disabled.

< 7ore e"pensive because of the cost of the concentrators.

Tree Topoloy

< * tree topology &hierarchical topology' can be viewed as a collection of star networks

arranged in a hierarchy.

< This tree has individual peripheral nodes which are re%uired to transmit to and receive fromone other only and are not re%uired to act as repeaters or regenerators.

< The tree topology arranges links and nodes into distinct hierarchies in order to allow greater

control and easier troubleshooting.

< This is particularly helpful for colleges, universities and schools so that each of the connect

to the big network in some way.

Advantaes of a Tree Topoloy

< (oint-to-point wiring for individual segments.

< )upported by several hardware and software vendors.< *ll the computers have access to the larger and their immediate networks.

Disadvantaes of a Tree Topoloy

< verall length of each segment is limited by the type of cabling used.

< If the backbone line breaks, the entire segment goes down.

< 7ore di0cult to congure and wire than other topologies.

Mesh Topoloy

< In this topology, each node is connected to every other node in the network.

< Implementing the mesh topology is e"pensive and di0cult.

< In this type of network, each node may send message to destination through multiple paths.

< +hile the data is travelling on the 7esh ;etwork it is automatically congured to reach the

destination by taking the shortest route which means the least number of hops.

Advantae of Mesh Topoloy

< ;o tra0c problem as there are dedicated links.

< It has multiple links, so if one route is blocked then other routes can be used for data

communication.

< (oints to point links make fault identication easy.

Disadvantae of Mesh Topoloy

< There is mesh of wiring which can be di0cult to manage.

< Installation is comple" as each node is connected to every node.

< 1abling cost is high.

)y%rid Topoloy


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< * combination of any two or more network topologies.

< * hybrid topology always accrues when two diFerent basic network topologies are

connected.

< It is a mi"ture of above mentioned topologies. Gsually, a central computer is attached with

sub-controllers which in turn participate in a variety of topologies.

Advantaes of a )y%rid Topoloy

< It is e"tremely 5e"ible.

< It is very reliable.

Disadvantaes of a )y%rid Topoloy

< 6"pensive

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