VCI (Virtual Channel Identifier)

Virtual Channel Identifier (VCI):

In computer networking, specifically in the context of Asynchronous Transfer Mode (ATM) networks, Virtual Channel Identifier (VCI) is a numerical value used to identify a specific virtual channel within an ATM network. ATM is a high-speed switching and multiplexing technology that transmits data in fixed-size cells, each consisting of 53 bytes.

ATM Basics:

In ATM networks, data is organized into virtual channels and virtual paths. A virtual path is a bundle of virtual channels that share the same path through the network. Each virtual channel within a virtual path is identified by its VCI value, which serves as a unique identifier for that particular virtual channel.

VCI Structure:

The VCI value is part of the ATM cell header and is used by ATM switches and routers to route the cell to the correct destination. The VCI value is 16 bits long, which means it can represent up to 2^16 (65,536) different virtual channels. The actual assignment of VCI values to virtual channels is managed by the ATM network's signaling and routing protocols.

VCI Usage:

When a user or device initiates communication in an ATM network, a virtual channel connection (VCC) is established between the source and destination endpoints. The VCI value is used to uniquely identify the VCC, along with the virtual path identifier (VPI), which identifies the virtual path to which the VCC belongs.

ATM switches and routers use the VCI value to make forwarding decisions, directing cells to the appropriate output port to reach their intended destination. As cells traverse through the ATM network, switches read the VCI value in the cell header and use it to determine the outgoing interface to forward the cell toward its destination.

VCI and VCIs Management:

The management of VCI values is a crucial aspect of ATM networks. VCI values must be assigned carefully to avoid conflicts and ensure proper routing within the network. The assignment of VCIs is typically handled by the network administrator or automated signaling protocols, such as the ATM Adaptation Layer 5 (AAL5) or the Signaling ATM Adaptation Layer (SAAL).

VCI in ATM Switching:

In an ATM switch, cells from different input ports may have the same VCI value. However, the VCI is only unique within the context of a specific virtual path. In combination with the VPI, the VCI value creates a globally unique identifier for each virtual channel connection in the entire ATM network.

Conclusion:

The Virtual Channel Identifier (VCI) is a numerical value used to uniquely identify individual virtual channels within an ATM network. It is part of the ATM cell header and is used by ATM switches and routers to route cells to their correct destinations. Proper management and assignment of VCI values are essential for ensuring the efficient and error-free operation of an ATM network.