ATM VC/VP Concept

The VP (virtual path) concept enables a bundle of VC’s (virtual circuits) to be handled as a whole by intermediate nodes, thus avoiding per VC processing operations. For example, two end systems connected by means of a VP can control the share of the bandwidth available on the VP to many VC’s in a transparent manner with respect to the intermediate switches. The VPI/VCI labels in the ATM cell header have only local significance, that is, the VPI/VCI pair of a cell changes link by link. ATM switches implement only the physical and the ATM layers at the user plane, thus carrying out a set of simple operations on cell streams belonging to active connections. Physical- and ATM-layer operations, such as VCI/VPI label swapping and cell routing from input to the requested output port, are carried out in hardware, thus minimizing the cell switch crossing time.

Figure 1: Fixed-Length Cells, VP and VC