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226 APPENDIX B: PATHBUILDER S330/S310 MODULE AND APPLICATION OVERVIEW
Figure 163 Virtual Circuit Scheme
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
VPI 1
VPI 2
VPI 3
{
{
VCIs
VCIs
VCI 1 (Transmit)
VCI 1 (Receive)
{
Virtual
Circuit
Transmission
Path
LAN
AA
LAN
AB
LAN
BA
LAN
BB
VPI/VCI
2/35
VPI/VCI 1/33
PathBuilder S330/S310
n x T1 or
n x E1
Workstation 1
Workstation 2
PathBuilder
S330/S310
PathBuilder
S330/S310
A
B