Virtual Circuit (VC)

Definition - What does Virtual Circuit (VC) mean?

A virtual circuit is used in transportation of data over a packet switch computer network, in which it appears as if there is a physical path established between the final destination and source and through which all packets can be routed during the call.

As there is no resource allocation other than few space in circuit tables in case of virtual circuit and also the fact the packets does not have to carry the globally unique destination address, provides great advantages for using virtual circuit.

Techopedia explains Virtual Circuit (VC)

Virtual circuit is a connection which is oriented unlike datagram switching. The source and destination identifies a suitable path for virtual circuit before the actual data communication starts. For this, it makes use of all intermediate nodes, routing table and other additional parameters.

Once the data transmission is completed, the resources and values present for the virtual circuit are removed completely. There are two categories of virtual circuit, namely switched virtual circuit and permanent virtual circuit.

Switched virtual circuit is a virtual circuit in the connection is dynamically established based on the demand and is torn down completely once the transmission is complete. Permanent virtual circuit is one provided for continuous usage or repeated usage between the dame data terminals.

Advantages of using a virtual circuit:

  • Since the same direction is followed, the packets are delivered in proper order.
  • As there is no need for packets to contain the complete address, the overhead in the packets are comparatively smaller.
  • As the resources are provided during the call setup, the connection is considered most of the time reliable. If the call has been already setup, even during times of congestion, the preceding packets should move along.
  • Billing is more convenient and easy as the billing records can be generated as per call and not as per packet.

Disadvantages of using a virtual circuit:
  • Since each switch needs to allocate capacity for any generated traffic and also needs to store the call details, powerful switching equipment is essential in virtual circuits.
  • Difficulty exists when one considers the resilience provided to the loss of a trunks as a failure results in calls being routed through a different route.

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