Transcript Virtual Circuit

Datagram and Virtual Circuit
Network
Datagram Network

Two 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.
Datagram
A, B, C, D, E –
Users
Virtual Circuit
In 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 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 configurations
1.
Multidrop
2.
Point to point.
Multidrop

Here all the terminals are wired onto the
same multidrop line.
Point to point

Here each terminal has its own point-to-
point line to the controller.
Polling

Each terminal has to keep quiet until
the controller says “Go ahead”.

Details
of
polling
differ
for
the
multidrop controller and point-topoint controller.
Multidrop
Two methods are common
1. Roll-call polling
2. Hub polling.
Roll-call polling

Controller 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 polling

Here the controller polls the furthest
terminal from it.
Point-to-point(Star)
1.
Often uses roll-call polling
2.
It has no site address.
Multiplexing and concentration

Terminal controllers are classified as,
Multiplexer

A 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 multiplexing

If each terminal operates at 1200 bps, the
output line must be 4 X 1200 = 4800 bps.
Concentrators
Identify the difference between Multiplexer
and Concentrator
Routing

Routing is the process of selecting paths
in a network.
Dijkstra's algorithm
Step1- Determine the shortest path from
node 1
Step 2- The shortest path from node1 is
2.
Step 3 - From 2 determine the next route.

But the distance between nodes1 and 3 is only 9
Step 4 - Choose node 3.
Step 5 - From 3 determine the next route.
Step 6 - Choose node 6.
Step 7 - From 6 determine the next route.
Shortest route is 1-3-6-5
Distance - 20

Thank You