3Com CoreBuilder 9000, Руководство пользователя

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354 C
HAPTER
13: E
STABLISHING
ATM C
HANNELS
Signaling —
External Links
This section describes establishing a switched virtual channel by signaling.
As discussed previously, a virtual channel is made up of two types of links:
External links (connections) between ports of adjacent ATM devices
Internal links between input and output ports of an ATM device stored
in the ATM Enterprise Switch matrix.
These two types of links are established in two different ways. The
external links are established by signaling; the internal links are
established by routing. Figure 17 illustrates the establishing of a virtual
channel. External links 2 and 4 are established by signaling; internal link 3
is established by routing.
Figure 17 Establishing a Virtual Channel
AT M Edge Device
ATM Edge Device
Destination Station
Transm itting Station
ATM Switch
The ATM switch
accepts or rejects
the proposed call
requirements
The VPI/VCI
values are fixed by
the ATM switch
and returned to the
edge device.
To initiate a virtual
channel a SETUP
command
is sent
by the edge
device.
containing the
requirements for
the call, except for
VPI/VCI,
The ATM Switch
selects the best output
port according to the
routing algorithm.
The port and VPI/VCI
information is stored in
the switch matrix.
A SETUP command
containing all
requirements for the
call is sent by the
output port of the
switch.
The edge device
accepts or rejects
the proposed call
requirements.
If accepted, the
VPI/VCI values
are fixed for this
connection.
VPI=0
VCI=32
VPI=1
VCI=44