3Com SuperStack II PathBuilder S330 Reference Manual page 238

226 A B: P B
PPENDIX ATH UILDER
S330/S310 M A
ODULE AND PPLICATION
Figure 163 Virtual Circuit Scheme
{
Virtual
VCI 1 (Transmit)
Circuit
VCI 1 (Receive)
VCIs
VCIs
Figure 164 illustrates this on a network using PathBuilder S330s. Suppose
workstation 1 on LAN AA wants to send data to workstation 2 on LAN BB. It
transmits Ethernet packets which include its MAC address and that of workstation
2. PathBuilder S330 A groups the packets into cells and, since it does not know
where workstation 2 is, broadcasts the cells on all VPI/VCIs. PathBuilder S330 B
learns that workstation 1 transmits to its T1/E1 UNI port over VPI/VCI 1/33 and
VPI/VCI 2/35. This information is then stored in forwarding tables in
PathBuilder S330 B.
When workstation 2 responds, it includes its MAC address and that of
workstation 1 in the packets. PathBuilder S330 B looks in the appropriate
forwarding table and finds that it can reach workstation 1 on VPI/VCI 2/5. When
the first response cell on 2/35 is formatted back into packets at PathBuilder S330
A, then PathBuilder S330 B learns how to reach workstation 2 without
broadcasting.
Figure 164 Virtual Circuits in a Simple Network
Workstation 1
LAN
AA
PathBuilder
S330/S310
LAN
AB
PathBuilder S330/S310
O
VERVIEW
VPI 1
VPI 2
{
VPI 3
{
VPI/VCI 1/33
n x T1 or
n x E1
A
VPI/VCI
2/35
Transmission
Path
LAN
BA
PathBuilder
S330/S310
B
LAN
BB
Workstation 2