User's Manual

Prestige 660R-6xC Series User’s Guide
Appendix E Virtual Circuit Topology 266
Appendix E
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:
• Virtual Channel Logical connections between ATM switches
• Virtual Path A bundle of virtual channels
• Virtual CircuitA series of virtual paths between circuit end points
Figure 184 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.
Your ISP (Internet Service Provider) should supply you with VPI/VCI numbers.