P-660R/H-D Series User’s Guide

Appendix C

Virtual Circuit Topology

ATM is a connection-oriented technology, meaning that it sets up virtual circuits over which end systems communicate. The terminology for virtual circuits is as follows:

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Virtual Channel

Logical connections between ATM switches

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Virtual Path

A bundle of virtual channels

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Virtual Circuits

A series of virtual paths between circuit end point

Figure 217 Virtual Circuit Topology

Think of a virtual path as a cable that contains a bundle of wires. The cable connects two points and wires within the cable provide individual circuits between the two points. In an ATM cell header, a VPI (Virtual Path Identifier) identifies a link formed by a virtual path; a VCI (Virtual Channel Identifier) identifies a channel within a virtual path.

The VPI and VCI identify a virtual path, that is, termination points between ATM switches. A series of virtual paths make up a virtual circuit.

Appendix C Virtual Circuit Topology

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