3Com 3C63311 Reference Guide - Page 238
PathBuilder S330 B.
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226 APPENDIX B: PATHBUILDER S330/S310 MODULE AND APPLICATION OVERVIEW Figure 163 Virtual Circuit Scheme { Virtual VCI 1 (Transmit) Circuit VCI 1 (Receive) { VCIs { VCIs VPI 1 VPI 2 VPI 3 Transmission Path 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 VPI/VCI 1/33 LAN AA n x T1 or n x E1 PathBuilder S330/S310 A LAN VPI/VCI AB 2/35 PathBuilder S330/S310 B LAN BA LAN BB PathBuilder S330/S310 Workstation 2