The next field contains the reference made to the VCI / VPI (Virtual Channel Identifier / Virtual Path Identifier). The role of virtual paths is to provide semi-permanent connections.
The virtual circuit (VC), the virtual circuit connection (VCC), the virtual path (VP) and virtual path connection (VPC) are defined as follows:
• The virtual circuit or VC (Virtual Channel) is a generic term used to describe the communication capacity for the transport of ATM cells. A virtual circuit identifier, VCI or, conventionally called commutation reference, is assigned to a VC connecting transporting ATM cells between two ATM nodes. The ATM node, wherein the VCI value is translated, is also called an ATM switch.
• The virtual circuit connection, or VCC (Virtual Channel Connection), defines the end to end connection between two access points to the AAL. a VCC is composed by concatenating one or more VC.
• The VP or VP (Virtual Path) is a VC beam. All VC of a bundle have the same end nodes.
• The virtual path connection, or VPC (Virtual Path Connection), consists of the concatenation of one or more VP. The ATM node is then called a fan.
Figure shows the VP / VC hierarchy and Figure Examples of VPC and VCC. The journey of a VPC is established by a routing in intermediate brewers (A, B and C for VP1 in Figure).
The nodes of the upper part of FIG are switches. Brewers do not participate in the administration of the bandwidth of the virtual paths.