3Com CoreBuilder 7000, Operation Manual, Page: 132 / 264

132 C
HAPTER
6: ATM S
WITCHING
ATM Switching
ATM switching is performed at the ATM layer through virtual channels.
Individual cells are switched over the channel through the network based
on the cell header.
Figure 42 Cell Flow in ATM Switching
Figure 42 shows how a call is transferred over a virtual channel. It is
assumed that the virtual channel has been established by one of the
methods described in the previous chapter. This means that the VPI/VCI
values for all external links are stored at the ports and the input/output
port associations for the internal links are stored in the switch.
ATM Edge Device
ATM Edge Device
ATM E dge Device
ATM Switch
ATM edge device
converts packets
A, B into cells a,b,
writes the VPI/VCI
in each cell header
and transmits
them over the two
virtual channels
VCa and VCb.
VCa and VCb are
multiplexed over
the same physical
line.
Two calls, A and
B, are initiated by
Ethernet end-
stations.
ATM Switch receives
cells, reads the VPI/VCI
and routes them to
correct output ports
according to the virtual
channel internal link. The
output port transmits
them to the ATM edge
devices over the virtual
channel UNI link.
ATM Edge Device
receives cells,
converts them into
packets and routes
them to the correct
Ethernet output
port.
bbbbbb
a aa
bb b
aaaaaa
VCa
VCa
VCb
VCb
bbbbbb
A
A
B
B
aaaaaa