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Short note: Virtual-circuit network

Short answer

A virtual-circuit network establishes a logical connection before data transfer, so all packets follow the same path and arrive in order. It uses short VC identifiers instead of full addresses, with setup, data transfer, and teardown phases. Resources can be reserved, and VCs may be switched (per call) or permanent (configured).

Write a short note on virtual-circuit network.

A virtual-circuit (VC) network is a packet-switched network in which a logical connection is set up between source and destination before data transfer. All packets of the session follow the same route and arrive in order, although link capacity is still shared with other users (it is "virtual", not a dedicated circuit). Examples: X.25, Frame Relay, ATM, MPLS.

Three phases

  1. Setup: a call-request packet travels through the switches; each switch makes an entry in its table and assigns a virtual circuit identifier (VCI) for the incoming and outgoing port.
  2. Data transfer: each packet carries only the short VCI; switches look it up and forward (label swapping).
  3. Teardown: a clear packet removes the table entries.
 Switch table:
 In port | In VCI | Out port | Out VCI
    1    |   14   |    3     |   22
 A --[VCI 14]--> S1 --[VCI 22]--> S2 --> B

Features

  • Short header (VCI instead of full address).
  • In-order delivery; resources and QoS can be reserved at setup.
  • Setup delay; if a switch fails, the VC is lost and must be re-established.

Types: switched VC (SVC, set up per call) and permanent VC (PVC, configured by the operator).

✓ Answer checked by Claude Opus 5.5 (high effort)

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