Virtual Circuit is the computer network providing connection-oriented service. It is a connection-oriented network. In virtual circuit resource are reserve for the time interval of data transmission between two nodes. This network is a highly reliable medium of transfer. Virtual circuits are costly to implement.
Working of Virtual Circuit:
- In the first step a medium is set up between the two end nodes.
- Resources are reserved for the transmission of packets.
- Then a signal is sent to sender to tell the medium is set up and transmission can be started.
- It ensures the transmission of all packets.
- A global header is used in the first packet of the connection.
- Whenever data is to be transmitted a new connection is set up.
Congestion Control in Virtual Circuit:
Once the congestion is detected in virtual circuit network, closed-loop techniques is used. There are different approaches in this technique:
- No new connection –
No new connections are established when the congestion is detected. This approach is used in telephone networks where no new calls are established when the exchange is overloaded.
- Participation of congested router invalid –
Another approach to control congestion is allow all new connections but route these new connections in such a way that congested router is not part of this route.
- Negotiation –
To negotiate different parameters between sender and receiver of the network, when the connection is established. During the set up time, host specifies the shape and volume of the traffic, quality of service and other parameters.
Advantages of Virtual Circuit:
- Packets are delivered to the receiver in the same order sent by the sender.
- Virtual circuit is a reliable network circuit.
- There is no need for overhead in each packet.
- Single global packet overhead is used in virtual circuit.
Disadvantages of Virtual Circuit:
- Virtual circuit is costly to implement.
- It provides only connection-oriented service.
- Always a new connection set up is required for transmission.
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