3Com S330 manual Virtual Circuit Scheme

226APPENDIX B: PATHBUILDER S330/S310 MODULE AND APPLICATION OVERVIEW

Figure 163 Virtual Circuit Scheme

Transmission

Path

Virtual		VPI 1
	VCI 1	(Transmit)
Circuit	{VCI 1	(Receive)

VPI 2

VCIs {

VPI 3

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

	VPI/VCI 1/33
LAN		n x T1 or
AA
		n x E1
	PathBuilder
	S330/S310
LAN	A
	VPI/VCI
AB	2/35

PathBuilder S330/S310

LAN

BA

PathBuilder

S330/S310

B

LAN

BB

Workstation 2