Prestige 641 ADSL Internet Access Router
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Appendix B
Appendix B
VPI & VCI
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:
l
VC (virtual channel)
Logical connections between end stations
l
VP (virtual path)
A bundle of VCs
Think of a VP 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 and a VCI (Virtual Channel Identifier) identifies a
channel within a virtual path. The VPI and VCI are identified and correspond to termination points at ATM
switches as shown. Your telephone company should supply you with these numbers.
Diagram 3 VPI's & VCI's.