3Com CoreBuilder 7000, Руководство по эксплуатации

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98 C
HAPTER
5: E
STABLISHING
ATM C
HANNELS
This section discusses the external link, established by signaling. For a
discussion of the internal links, which are established by routing, see
“Routing — Internal Links” on page 125 in the Management Guide.
A simple example of a virtual channel is shown as a dashed line in
Figure 35.
Figure 35
Virtual Channel Passing through ATM Network Devices
The figure shows three ATM devices: two ATM edge devices and an ATM
switch between them. The virtual channel begins at the left edge device,
passes through the switch and terminates at the right edge device. Two
external links of the virtual channel, shown as
2
and
4
connect output
ports of one device with input ports of the adjacent device; the internal
link within the switch, shown as
3,
associates the input port of the switch
with the correct output port.
ATM Edge Device
ATM Edge Device
Destination Station
Transmitting Station
ATM Switch
The virtual channel
starts at the ATM
edge device.
A VPI/VCI pair is
associated with
the virtual channel
by both the output
port of the edge
device and the
input port of the
switch.
The source station
is connected to an
Ethernet port of
the attached ATM
edge device
The ATM switch has
been setup to associate
the specific VPI/VCI pair
on the input port with
another VPI/VCI pair on
an output port.
A VPI/VCI pair is
associated with the
virtual channel by both
the output port of the
switch and the input port
of the edge device
The virtual channel
terminates at the
edge device.
The ATM edge
device associates
the VPI/VCI
information with
the destination
Ethernet output
port.
The Ethernet
output port of
the edge device
is connected to
the destination
station.
VPI=0
VCI=32
VPI=1
VCI=44
1
1
2
2
3
3
4
4
5
5