AT&T IP Flexible Reach and AT&T IP Flexible Reach with AT&T Business in a BoxNortel BCM50 Release 3.0 SIP Configuration Guide*Nortel, Nortel Networks, Nortel (Logo), the Globemark, CS1000 are trademarks of Nortel Networks.Issue 1.5 Page 22 of 384.3.1 Failover to Secondary AT&T IP Border Element (IPBE) – NOTSUPPORTED ON AT&T IP Flexible Reach with AT&T BUSINESS INA BOXFor AT&T IP Flexible Reach with AT&T Business in a Box customers, please skipthis section and continue on to Section 4.4.Backup to a secondary AT&T IP Border Elements is supported on the BCM50using the SIP “OPTIONS” keep-alive approach. The BCM50 will send SIP“OPTIONS” messages to the AT&T IPBEs listed in the Outbound Proxy Table andsend VoIP calls based on whether or not the BCM50 receives a “200 OK” fromthe IPBEs and the Load-balancing Weights values set for each entry.Figure 15: Outbound Proxy Table for failover to secondary AT&T IPBEsA Load-balancing weight of 0 means the IPBE is used as last resort. Any non-zero number value indicates the ratio of calls (the specific IPBE’s load-balancingweight to sum of all IPBE’s load-balancing weights) the BCM50 will send out toeach IPBE. In this example, the BCM50 will send 1 call for every 1 call made (inessence, all calls) to the IPBE with IP address 135.25.29.135 and use135.25.29.79 IPBE as backup.