What is a Virtual Circuit Identifier (VCID)?

A Virtual Circuit Identifier (VCID or VCI) is a label assigned to each virtual circuit in a packet-switched network that determines the path a data unit must follow from source to destination.

A virtual circuit (VC) is a communication technique that creates the appearance of a dedicated physical connection between two systems, even though the data actually travels through a shared packet-switched network infrastructure.

How Virtual Circuits Work

VCIDs enable efficient network resource utilization by allowing multiple virtual circuits to share the same physical links simultaneously. The same VCID can be reused on different network segments for connections with non-overlapping paths, maximizing the number of concurrent connections the network can support.

VCI in ATM Networks

Asynchronous Transfer Mode (ATM) is a switching technology that uses time division multiplexing for data communications, supporting voice, video, and data transmission. ATM encodes information into small, fixed-size cells (53 bytes each) for transmission over the physical medium.

Each ATM cell contains a VCI field in its 5-byte header, which switches use to forward cells along predetermined virtual circuit paths. The VCI works in conjunction with the Virtual Path Identifier (VPI) to create a hierarchical addressing scheme that enables efficient routing and switching.

Key Features of VCIDs

Conclusion

Virtual Circuit Identifiers enable efficient packet forwarding in connection-oriented networks by providing local labels that switches use to forward data along established virtual circuits. This approach allows multiple connections to share network resources while maintaining the appearance of dedicated communication paths.