3Com SuperStack II PathBuilder S330 Reference Manual page 260

252 A B: P B
PPENDIX ATH UILDER
S330/S310 M A
ODULE AND PPLICATION
Figure 179 Virtual Circuit Scheme
{
Virtual
VCI 1 (Transmit)
Circuit
VCI 1 (Receive)
VCIs
VCIs
Figure 180 illustrates this on a network using PathBuilder S330 switch. Suppose
workstation 1 on LAN AA wants to send data to workstation 2 on LAN BB. It
transmits Ethernet packets that include its MAC address and that of
workstation 2. Switch A groups the packets into cells and, since it does not know
where workstation 2 is, broadcasts the cells on all VPI/VCIs. Switch 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 Switch B.
When workstation 2 responds, it includes its MAC address and that of workstation
1 in the packets. Switch 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 Switch A, then Switch B learns how to reach
workstation 2 without broadcasting.
Figure 180 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