Datagram and Virtual Datagram and Virtual CircuitCircuit

NetworkNetwork

Datagram NetworkDatagram NetworkTwo packets of the same user

pair can travel along different routes.

The packets can arrive out of sequence.

Packets contain full Source, Destination addresses.

Requires no connection setup.

DatagramDatagram

A, B, C, D, E – Users

Virtual CircuitVirtual CircuitIn a virtual circuit network. Virtual Circuit(connection

setup) is required.

All packets of the same virtual circuit travel along the same path.

Packet sequencing is guaranteed.

Packets contain short Virtual Circuit Id. (VCI).

First packet has large delay.

Terminal HandlingTerminal Handling

For many applications cost of communication lines exceeds the cost of equipment connected by those lines.

Here we have a terminal controller which accepts many input and gives a single output.

Types of configurationsTypes of configurations

1.Multidrop2.Point to point.

MultidropMultidropHere all the terminals are wired

onto the same multidrop line.

Point to pointPoint to pointHere each terminal has its own

point-to- point line to the controller.

PollingPolling

Each terminal has to keep quiet until the controller says “Go ahead”.

Details of polling differ for the multidrop controller and point-to-point controller.

Multidrop Multidrop

Two methods are common1. Roll-call polling 2. Hub polling.

Roll-call pollingRoll-call pollingController sends a message to

each terminal in turn, inquiring whether or not terminal has anything to say.

These polling messages contain site address or station address identifying which terminal is being addressed.

Each terminal knows its own address and only responds to its own polls, although it receives all the polls.

Hub pollingHub pollingHere the controller polls the

furthest terminal from it.

Point-to-point(Star)Point-to-point(Star)

1. Often uses roll-call polling 2. It has no site address.

Multiplexing and Multiplexing and concentrationconcentration

Terminal controllers are classified as,

MultiplexerMultiplexerA multiplexer is a device that

accepts input from a collection of lines in some static, predetermined sequence, and outputs the data onto a single output line in the same sequence.

Four terminal multiplexingFour terminal multiplexing

If each terminal operates at 1200 bps, the output line must be 4 X 1200 = 4800 bps.

ConcentratorsConcentrators

Identify the difference between Identify the difference between MultiplexerMultiplexer

and Concentratorand Concentrator

RoutingRouting

Routing is the process of selecting paths in a network.

Dijkstra's algorithmDijkstra's algorithm

Step1- Step1- Determine the shortest path Determine the shortest path from from node 1 node 1

Step 2- Step 2- The shortest path from The shortest path from node1 is node1 is 2. 2.

Step 3 - Step 3 - From 2 determine the From 2 determine the next route.next route.

But the distance between nodes1 and 3 is only 9

Step 4 - Step 4 - Choose node 3. Choose node 3.

Step 5 -Step 5 - From 3 determine the From 3 determine the next route. next route.

Step 6 - Step 6 - Choose node 6. Choose node 6.

Step 7 - Step 7 - From 6 determine the From 6 determine the next route. next route.

Shortest route is 1-3-6-5

Distance - 20

http://upload.wikimedia.org/wikipedia/commons/4/45/Dijksta_Anim.gif

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