circuit switching packet switching message switching wcb/mcgraw-hill the mcgraw-hill companies,...

22
Circuit Switching Packet Switching Message Switching WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Upload: valerie-hamilton

Post on 01-Jan-2016

239 views

Category:

Documents


1 download

TRANSCRIPT

Circuit Switching Packet Switching Message Switching

WCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

Switching Circuit Switching Message switch Packet Switching Packet Switching Techniques Datagram Approach Virtual Circuit Approach Virtual Circuits Vs Datagram

The process of transfering data blocks from one node to another is called switching.

In a switched communications network, data entering the network from a station are routed to the destination by being switched from node to node.

Data entering the network from a station are routed to the destination by being switched from node to node.

uses a dedicated path between two stations

has three phases◦ establish◦ transfer◦ disconnect

Inefficiento channel capacity dedicated for duration of connectiono if no data, capacity wasted

set up (connection) takes time

once connected, transfer is transparent

back

Circuit switching:

There is a dedicated communication path between two stations (end-to-end)

◦ The path is a connected sequence of links between network nodes. On each physical link, a logical channel is dedicated to the connection.

Communication via circuit switching has three phases:◦ Circuit establishment (link by link)

Routing & resource allocation (FDM or TDM)◦ Data transfer◦ Circuit disconnect

Deallocate the dedicated resources

Simple

Once the circuit is established, data is transmitted with no delay.

Uneconomical method.

Time required to established a physical link between two station is very large.

Network resources are not properly utilised.

back

Sending device appends the destination address to the message

Passes it to the network from one node to another node till it reaches to the intended destination.

Switching node receive the message ,store it and then transmit it to the next node.

No physical connection is required between source and destination node.

This method uses the communication channel very effectively because channels are used when messages are transmitted.

This method is slow for interactive real time application.

As message length is unlimited (not fixed),each node must have sufficient storage to store message.

A message is delayed at each node.

back

packet switching was designed for data

transmitted in small packets

packets contains user data and control infouser data may be part of a larger messagecontrol info includes routing (addressing) info

packets are received, stored briefly (buffered) and past on to the next node

line efficiency single link shared by many packets over time packets queued and transmitted as fast as possible

data rate conversion stations connects to local node at own speed nodes buffer data if required to equalize rates

packets accepted even when network is busy

priorities can be used

back

station breaks long message into packets

packets sent one at a time to the network

packets can be handled in two waysdatagramvirtual circuit

back

Each packet treated independently

Packets can take any practical route

Packets may arrive out of order

Packets may go missing

Up to receiver to re-order packets and recover from missing packets

back

Preplanned route established before any packets sent

Call request and call accept packets establish connection (handshake)

Each packet contains a virtual circuit identifier instead of destination address

No routing decisions required for each packet

Clear request to drop circuit

Not a dedicated path

back

virtual circuits◦ network can provide sequencing and error control◦ packets are forwarded more quickly◦ less reliable

datagram◦ no call setup phase◦ more flexible◦ more reliable

back