External Links - Atm Connections; Internal Link - Switch Matrix; Virtual Path - Channel Hierarchy - 3Com CoreBuilder 7000 Operation Manual

External Links – ATM
Connections
Internal Link —
Switch Matrix
Virtual Path —
Channel Hierarchy
Each external link, referred to as an ATM connection, is uniquely
characterized by a pair of integers VPI and VCI called the Virtual Path
Identifier and Virtual Channel Identifier. The default range is VPI: 0-7; VCI:
32-511VPI: 0-2 8 ; VCI: 0-2
The VPI/VCI pairs are allocated by the ports at both ends of the external
link. For example, the values VPI/VCI=0/32 in link
output port of the edge device and the input port of the ATM switch. The
fact that separate devices can allocate exactly the same VPI/VCI value is
the result of UNI signaling negotiation between them during
establishment of the virtual channel. For more information about UNI
signaling, see "Signaling — External Links" on page 104 in the
Management Guide.
The virtual channel is completed by adding the internal link inside the
ATM devices. The internal link does not run over a fixed cable like the
external link but is rather a correspondence between the adjacent
external links which is stored in the internal memory matrix of the switch.
The ATM switch stores the correspondence
its internal memory matrix. Thus the VPI/VCI values of link
specific input port of the switch are associated with the VPI/VCI values of
link at the specific output port of the switch. As above, this
4
correspondence is established during the signaling phase.
The values of VPI and VCI can be allocated independently of each other.
These two degrees of freedom allow a channel hierarchy to be
constructed. If several virtual channels with different VCI values are given
the same VPI value, then all these channels can be grouped together by
relating only to the VPI value. A virtual channel defined by its VPI only is
called a virtual path.
For the purposes of switching, a virtual path with a certain VPI value is as
a high-level "container" channel that carries all virtual channels with that
common VPI value; when the virtual path is switched, all the virtual
channels are also switched.
16 .
between link
3
Virtual Channels 99
were allocated by the
2
and link
2 4
at the
2
in