Cabletron Systems MMAC-Plus SFCS-1000, Configuration Manual

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1-11
Configuring PVCs
Virtual channels switch cells using both the VPI and VCI values. Both the VPI
and VCI values may change when a cell is switched via a virtual channel. For
example, the virtual channel C2|1|20 -> D2|9|25 will switch cells received
on port C2 with VPI: 1 and VCI: 20 such that they are transmitted out port D2
with VPI: 9 and VCI: 25.
Figure 1.9 - Example of a Virtual Channel
In order to establish two-way communications between two ports on a switch
fabric, two virtual channels are necessary because virtual channels are unidi-
rectional. For example, switch fabric A is configured with the virtual channel
C3|7|12 -> D1|8|2. If a cell is received on port D1 with VPI: 8 and VCI: 2, it
will not be transmitted out port C3 with VPI: 7 and VCI: 12. An additional
channel, namely D1|8|2 -> C3|7|12, would have to exist.
Figure 1.10 - Virtual Channels are Unidirectional
switch fabric
cell
cell
VPI: 9
VPI: 1
D2
C2
VCI: 25
VCI: 20
Virtual Channel
C2|1|20 -> D2|9|25
C3
D1
C3|7|12 -> D1|8|2
D1|8|2 -> C3|7|12