Ethernet Interface (10BASE-T or 10/100BASE-T)
253
The aggregate of VPIs/VCIs assigned to the Ethernet connection of the PathBuilder
S330/S310 switch is referred to as a bridge. Since the switch reads and stores
MAC addresses and associated VPIs/VCIs as described above, the bridge is called a
learning bridge. Each learning bridge of the PathBuilder S330/S310 switch has a
separate forwarding table containing the MAC address to VPI/VCI associations.
When a learned entry is stored in a forwarding table, it is time tagged. An aging
timer in the switch, which you set, purges entries from the forwarding tables after
they have been in the tables for the aged time. The bridges must then relearn
purged addresses. This controls the size of the forwarding tables, particularly in
large networks.
In the switch, each bridge also has a static table associated with it. You can enter
MAC addresses and corresponding VPIs/VCIs into the static table that will not be
affected by the aging timer. These entries might be for LAN units that are relatively
permanent and are accessed through the ATM network frequently, such as servers.
In the example shown in Figure 180, there is only one transmission path: the T1/n
x T1 (or E1/n x E1) between the two PathBuilder S330 switches, so cells leaving
Switch A on VPI/VCI 1/33 arrive at Switch B on VPI/VCI 1/33. Also if theT1/nxT1 (or
E1/n x E1) trunk were switched through a standard telephone switching system to
interconnect many PathBuilder S330 switches, each switch would have to have
the same VPI/VCI designations assigned. The ATM switch removes this restriction.
Figure 181 shows several PathBuilder S330/S31 switches in an ATM-switched
network. The switch maps one VPI/VCI into another based on the destination of
the packets in the cell. It learns the complete topology of the network to do so.
You can independently configure each PathBuilder S330/S310 switch connected
to the ATM switch.
Figure 181
Virtual Circuits in a Switched Network
PathBuilder S330/S310 A
PathBuilder S330/S310 C
PathBuilder S330/S310 B
ATM
Switch
VPI/VCI 2/6
VPI/VCI 1/3
VPI/VCI 3/23
