Networking Basic Concepts Lecture 2 Web Technology

8/4/2019 Networking Basic Concepts Lecture 2 Web Technology

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Networking Basic Concepts

Computer Networks

A communication system for connecting computers /

hosts.

Better connectivity

Better communication

Better sharing of resources Bring people together


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Types of computer networks

Geographical Span

Connects hosts within a relatively

small geographical area. Same room

Geographical Span

Hosts may be widely dispersed

Across the campuses Across cities countries / countries /

Local Area Network Wide Area Network

Same building

Same campus

Speed

Faster

Typical Speed is 10 Mbps to 10 Gbps

Cost Cheaper

Ownership Issue

Physical transmission media

continents

Speed

Slower

Typical Speed is 64 Kbps to 8 Mbps

Cost Enterprise

Ownership Issue

Physical transmission media


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Types of computer networks

Communication


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Circuit Switching

A dedicated path is required between two stations

A path follows a fixed sequence of intermediate links

A logical channel gets defined on each physical link

Dedicated to the connection

FB

A

E

D

GC

H


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Circuit Switching (contd.)

In Circuit Switching three steps are required for

communication:-

Connection establishment

Required before data transmission

Data transfer

Can proceed at maximum speed

Connection termination

Required after data transmission is over

For deallocation of network resources


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Circuit Switching (contd.)

Drawbacks:-

Channel capacity gets dedicated during the entire

duration of communication

Acceptable for voice communication

Very inefficient for bursty traffic

There is an initial delay

For connection establishment


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Packet switching

Modern form of long distance data communication

Network resources are not dedicated

A link can be shared

The basic concept remained the same

Widely used for long distance data communication


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Packet switching (contd.)

Data are transmitted in short packets (Kbytes)

A longer message is broken up into smaller chunks

The chunks are called as packets

Ever acket contains a header

Relevant information for routing, etc


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Message

H H H

Packets


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Packet switching is based on stored-and-forward

concept

Each intermediate network node receives whole packet

Decides to route

Forwards the packet along selected


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Advantages

Link can be shared so link utilization better

Suitable for computer generated traffic

Typically bursty in nature

Buffering and data rate conversion can be performed

easily

Some packets given priority over others if desired


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How are the packets transmitted?

Two alternative approaches

1. Virtual circuits

2. Data rams

The abstract network model is same

FB

A

E

D

GC

H


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Virtual circuit approach

Similar to the concept of circuit switching

A route is established before packet transmission starts

All packets follow same path

The links com risin the ath are not dedicated

Different from circuit switching in this respect

Analogy

Telephone system


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Virtual circuit approach (contd.)

How it works?

Route is established a priori

Packet forwarded from one node to the next using

stored-and-forward scheme n y virtua circuit num er nee to e carrie out y

the packet Each intermediate node maintains a table created during

route establishment

Used for packet forwarding

No dynamic routing decision was taken by intermediatenodes


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Datagram approach

Basic concept

No route is established before hand

Each packet is transmitted as an independent entry

Does not maintain an histor

Analogy Postal system


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Datagram approach (contd.)

Every intermediate node has to take routing decision

automatically

Makes the use of routing table

Every packet must contain source and destination address

Problems:-

Packets may be deliver out of order

If the node crashes momentarily, all of its queued packets

are lost

Duplicate packets may also be generated


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Datagram approach (contd.)

Advantages:-

Faster then virtual circuit approach for smaller number

of packets

No route establishment and termination

More flexible

Packets between two host may follow different path

Can handle the congestion link


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Comparative study

Three types of delays must be considered:

1) Propagation delay

Time taken by the data signal to propagate from one

2) Transmission delay

Time taken to send out packet by a transmitter

3) Processing delayTime taken by node to process the packet


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Circuit switching

After initial circuit establishment data bits are sent

continuously without any delay


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Virtual circuit Packet switching

Call request packet sent from source to destination

Call accept packet returns back

Packets sent sequentially in pipelined fashion


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Datagram Packet switching

No initial delay

The packets are sent out independently

Many follow different paths

- -


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Layered network architecture

Open Systems Interconnection (OSI) reference model

Seven layer model

Communication functions are partitioned into

Systematic approach to design

Changes in one layer should not require changes in

other layer


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The 7 layer OSI Model

Application

Presentation Host to host

physical

Session

Transport

Network

Data Link

Point to point


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Layer function

Physical layer

Transmit row bit stream over physical medium

Reliable transfer of link over point to point link

Network layer Establishing, Maintaining and terminating connections

Routes the packet through point to point link


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Layer function (contd.)

Transport layer

End to end reliable data transfer

With error recovery flow control

Manages the session

Presentation layer

Provides data independence Application layer

Interface point for user application


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How data flows in 7 layer model?

Session

Application

Session

Application

presentation presentation

physical

Transport

Network

Data Link

physical

Transport

Network

Data Link

S DA B


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Internetworking Devices

Hub

Extends the span of single LAN

Bridge / layer-2 switch

Works at data link layer level

Router / Layer-3 switch

Connects any combination of LAN and WANWorks at network layer


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Campus network schematic

Department

NetworkDepartment

Network

Backbone

Backbone n/w: Fast Ethernet, FDDI, ATM, Gigabyte Ethernet

DN: Switched Ethernet, Bus based Ethernet

Department

Network

Department

Network

Network


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Connecting computer to departmental

network

Requires NIC

Connection through

switch or hub

Backbone network

shown

C C C

HUBHUB

Ethernet switch


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Connecting to outside world

Radio link

Satellite

Antenna

Institute

network

Router

Modem Telephone line

leased line

Networking Basic Concepts Lecture 2 Web Technology

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