Avaya 8800 Planning And Engineering page 214

Multicast network design
Figure 96: Avoiding an interruption of IGAP traffic
The following scenario shows how a potential traffic interruption can occur:
1. An authenticated IGAP member receives multicast traffic. Accounting starts.
2. R1 uses MLT1 to transfer data and accounting messages.
3. MLT1 goes down.
4. MLT2 redistributes the traffic that exists on MLT1.
MLT1 is down, so both the Accounting Stop and Accounting Start messages are sent to the
RADIUS server on MLT2. If the Accounting Stop message is sent before OSPF can recalculate
the route change and send an Accounting Start message, the switch drops the User Datagram
Protocol (UDP) packets.
This scenario does not cause an accounting error because RADIUS uses the session ID to
calculate accounting time. Even though the route loss and OSPF recalculation caused the
packets to be sent out-of-sequence, IGAP and RADIUS process the events in the correct order.
214 Planning and Engineering — Network Design
Because the (S,G) entry is deleted, an Accounting Stop message is triggered.
Because a new (S,G) entry is created with a different session ID, an Accounting
Start message is triggered.
November 2010