data communication networks 2

8/12/2019 data communication networks 2

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Data Communications &

Networking

An Introduction


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Scope of the course

The course introduces the concepts &mechanisms underlying the moderncommunication systems & networks

The Internet (TCP/IP) model is used asa framework to introduce different

protocols & standards


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Hierarchical structure of the course

Introduction to data communication and the Network model Introduction to networking

Network model, Physical topologies of networks, network categories etc

Layered network architecture

Protocols, syntax, semantics and timing of protocol

Two reference models(ISO/OSI and TCP/IP or internet model)

Understanding the different layers and its function of TCP/IPmodel The five layers as

Physical layer

Data link layer

Network layer

Transport layer

Application layer


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What is Data Communication?

What is networking?

How above two are interrelated?


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Network Model


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Effectiveness of the DCS depends on thefollowing fundamental characteristics

Delivery

Accuracy

Timeliness

Jitter


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Data Communications &

Networking

Components


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SR

Medium

Message

Rule 1:Rule 2:.

..Rule n:

Rule 1:Rule 2:.

.

.Rule n:

Protocol

Syntax

Semantics

Timing


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Direction of Data Flow

Simplex

Half duplex

Full Duplex


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Networks

Distributed Processing

Network Criteria

Physical Structures

Categories of Networks


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Network Criteria

Performance

Reliability

Security


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Type of Connection

Point-to-PointPoint-to-Multipoint


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SR

Point to -Point

Type of Connection

Point-to-PointPoint-to-Multipoint


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Physical Topology

Mesh

Star

Bus

Ring


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D

C

B

A

n(n-1)/2

Mesh


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Advantages

Avoids Traffic Problem

Robust Privacy or security

Fault id & isolation Easy

Disadvantages

Amount of Cabling and I/O ports moreInstallation & Reconnection are difficult

Expensive h/w to connect each link


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Hub

AC DB

Star


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Advantages

Less expensive than mesh

Easy installation and reconfiguration

Robustness

Easy fault identification and fault isolation

Disadvantages

Although star requires less cabling than mesh -

each node must be linked to a central hub morecabling is required as compared to bus and ring

Hub fails ntk down


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Cableend Cableend

A

Tap

DropLine

Tap

DropLine

Tap

DropLine

Bus

B C

Ad t


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Advantages

Ease of installation

Less Cabling

Disadvantages

Difficulty in reconnection and fault isolation

Bus cable is optimally efficient difficult to add newdevicesSignal reflection at taps can cause degradation in quality

If fault or break in the bus cable stops all tx

The damaged area reflects signal back in the direction oforigin creating noise in both direction


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Repeaters

Ring

A

B C

D

EF


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Advantages

Easy to install and reconfigure

To add /delete a device requires changingonly two connections

Fault isolation is simplified

Disadvantage

A break in ring can disable the entire ntk


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Hybrid


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Network Categories

LAN

MAN

WAN


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Protocols and Standards

Protocols

Standards

Standards Organization


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Protocols Protocol is set of rules that govern Data

communication.

The sender and the receiver, the two key

parties in data communication must agree on acommon set of rules before they cancommunicate with each other.

A protocol defines what is communicated, howit is communicated.


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Key Elements of protocol Syntax

(Structure or format of data)What is to be communicated

Semantics(Meaning of each section of bits) How it isto be communicated

Timing(when data should be sent and how fastthey can be sent) When it should be

communicated


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Standards

De facto

(by convention adopted as standardthrough widespread use)

De jure

(by law standards have been legislated

by an officially recognized body)


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Standards Organization

Standards creation committees

Forums

Regulatory Agencies (FCC)

S d d C i C i


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Standards Creation Committees

ISO (International Organization for standardization)

Technical recommendations for data communicationinterfaceITU-T (International Telecommunication Union-

Telecommunication Standards)Technical recommendations about telephone, telegraph and

data communications interfacesANSI (American National Standards Institute)-Coordinating organization for US (not a standards- making

body) www.ansi.org

IEEE(Institute of Electrical and Electronics Engineers)Professional society; also develops mostly LAN standardsstandards.ieee.org


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Standardization Process

Specification

Identification of choices

Acceptance


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Layered structure example

Organization A Organization B

Postal department Network

CEO-A CEO-B

PA-A

R&D Clerk-A

Mail-man-A

PA-B

R&D Clerk-B

Mail-man-B

Mail-Box-A

Mail-

Box-B

Ob ti f th b


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Observations from the aboveexample

communication process is divided into number ofsub functions.

The distribution of process into more than onefunction is brought about in order to enhance the

performance at each level. The function of the level above or above a certain

level is transparent at each level

Modification can be performed at each levelimproving or modifying its performance much easily.

The above example is a 7 Layer Model


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Peers

Each level in organization A is complementedby a corresponding level in organization B.These level which perform the complement

function are called peers. Peers may be defined more generally as

those parties functioning at the same levelappearing to communicate each other


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Service access points

The CEO-A accesses the PA-A anddictates the letter, this boundarybetween CEO-A Layer & PA-A layer is

called SAP. The SAP is almost two way as in case of

PA-B of organization B handling over the

letter to CEO-B


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Hierarchy:-

according to the analysis there are 6different activities at the sender side and 6at the receiver side. For completing the taskthe activities are performed in the order ie

in hierarchical manner. Services:-

Each function or layer uses services of thelayers immediately below it.


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Stack of layers

The layers which form the model are alsocalled stack of layers or layer stack.

This stack of layers is also called a protocolstack, since each layer is clearly defined aswhat services it will provide.

The rules and formats for interaction with itare well defined

Layering A vantages


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Layering A vantages

Complex problems are broken into an ordered

sequence of simpler problems. Hence solving ofcomplex problem becomes easier

The modularization of layers represents the

simpler problem may be modified and implementedwithout affecting the layer above and below it

Layering approach provides a broad commonfunctionality which enables a wide range ofimplementers to interface to various layers instandard manner

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