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24 Avidia System Configuration and Management User Manual
ATM Virtual Circuits
ATM virtual circuits are logical connections in the ATM network over which ATM cells
are transmitted between two points. Permanent Virtual Circuits (PVCs), supported by Avidia
systems, comprise a Virtual Path Connection (VPC) and, frequently, multiple Virtual Channel
Connections (VCCs) within the VPC. The VPCs and VCCs are mapped to a predefined static
route that is always in place and is always available.
The Avidia system functions as a VPC or VCC cross-connect switch, utilizing cross-connect
VPCs and VCCs to carry data between defined points within the Avidia chassis, such as
between a channel card and a line card. VPCs and VCCs also carry data from subscriber
modems to Avidia channel cards, and from Avidia line cards to other destinations in the ATM
backbone network.
VPC configuration requires specifying a Virtual Path Identifier (VPI). For VPCs, the system
only translates the VPI value and does not check or change any configured Virtual Channel
Identifier (VCI) value. VCC configuration requires specifying a VPI and a VCI. VPI and VCI
combinations must be unique only on the same user port, as the circuit is remapped to a different
VPI and VCI on the network interface. This enables different subscribers to use the same VPI
and VCI combinations without creating conflict in the network.
The valid VPI and VCI range depends on the type of cards used in the virtual circuit. Use the
following tables to determine valid values.
PVC Configuration
Card VPI Range
No. of VPIs per
port that can be
mapped to PVCs
VCI Range
Maximum no. of
connections that
can be mapped to
each port
(a)
(a) The system supports a maximum of 8188 total connections.
OC3 0-255 16 32-1023 4094
DS3 0-255 16 32-1023 4094
AMC 0 1 1024-4095 96
DSX-1/T1 user or network
interface (ATM)
0-255 3 32-1023 510
Cell-based ADSL channel
card (ATM)
0-255 4 32-253 40
Frame-based SDSL 0 1 1024-4095 3072
Cell-based SDSL (ATM) 0-127 4 32-127 40
Frame-based IDSL 0 1 1024-4095 3072