Cisco Systems 8600 Series manual Downstream on Demand Tag Allocation, Conservative Mode Shown

Tag Switching in an ATM WAN

Figure 9-3shows an example of conservative allocation. ATM edge TSR RTA is an IP routing peer to ATM-TSR RTB. In turn, ATM-TSR RTB is an IP routing peer to ATM-TSR-RTC. IP routing updates are exchanged over VPI/VCI 0/32 between RTA-RTB and RTB-RTC. For example:

1RTA sends a tag binding request toward RTB in order to bind prefix 128.89.0.0/16 to a specific VCI.

2RTB allocates VCI 40 and creates an entry in its TFIB with VCI 40 as the incoming tag.

3RTB then sends a bind request toward RTC.

4RTC issues VCI 50 as a tag.

5RTC sends a reply to RTB with the binding between prefix 128.89.0.0/16 and the VSI 50 tag.

6RTB sets the outgoing tag to VCI 50.

7RTB sends a reply to RTA with the binding between prefix 128.89.0.0/16 and the VCI 40 tag.

8RTA then creates an entry in its TFIB and sets the outgoing tag to VCI 40.

Optimistic mode operation is similar to that shown in Figure 9-3,except that the events labeled 7 and 8 in the figure may occur concurrently with event 3.

Figure 9-3 Downstream on Demand Tag Allocation, Conservative Mode Shown

9-6Cisco BPX 8600 Series Reference