What is virtual circuit switching?

You may know about circuit switching. In-circuit switching a dedicated path is set up between two ends.  The path may have multiple hops. At each hop, an incoming line joins an outgoing line.  No other communication flow can use a partial or full path.

What is a virtual circuit?

In a virtual circuit, a path is established between two ends over a packet-switched network e.g IP.  During a call, all media packets follow the same path. 

Although there is no dedicated reservation of a channel but looks like there is a physical path reserved between communicating parties.  So that’s why it’s called virtual circuit switching. 

Because it is a shared network, other parallel streams of packets may also share the same network partially or fully. Frame Relay is one of example for virtual switching network.

How and when do the virtual circuit forms?

One two parties decide to start a communication, both ends set up a virtual setting end to end. During the setup phase, each intermediate node makes an entry in the routing table for all packets that would associate with the connection. Packets may be identified with an integer identifier.  There could be other Quality of Service level parameters agreed upon connection setup.

Once after data transfer, if both sides end up the conversation. All resources for the circuit are freed and now available to others.

Advantages and Disadvantages of virtual circuit switching-

Along with any advantage or disadvantage, it mostly depends on the use case.  For example, the voice call is always circuit-switched.  There should be signaling to set up a circuit before any actual voice packet exchange.  But still, there are a few things that we need to know.

Advantages –  

  • All packet travels via the same path, so there will not any sequencing problems that an application should take care of.
  • Better utilization of underlying bandwidth, as each packet needs only to carry a circuit identifier, in place of the full address.  This enables more data transfer on the same channel capacity.
  • Controlling communication is each, each end knows when to start and when to stop.
  • Network resources are pre-allocated to lesser chances of congestion.
  • Option for Quality of service negotiation before the start of actual data transfer.
  • A lost packet can be detected and retransmitted. So it’s reliable communication.

Disadvantages – 

  • All intermediate nodes should have the capability for virtual circuit switching.
  • The resources are reserved, so a new connection may need to wait for a longer time.