o lower ones, SO configure this carefully to get the optimum negotiation with endpoints in your network and across the SIP trunk. Newer releases might support codec preference ordering con- figuration options. Configure alternate (redundant) PSTN routing if the SIP trunk is down. It is best not to remove TDM PSTN trunking and gateways from your network until after a SIP trunk has been proven in. Generally, a CUCM configuration for alternative PSTN routing includes Trunks contained in route groups Route groups contained in route lists Route lists used to cycle through alternative trunk destinations, as illustrated in Figure 11-2 Retry timers and counters tuned to optimize failover time to alternative trunks Return code mapping (SIP codes to Q.850) used to stop CUCM trunk selection when needed 260 SIP Trunking Route Group 1 Route Route Pattern Route Group 2 CUBE Pool Figure 11-2 CUCM Alternative Routing SBC Best Practices Best practices in the area of session border controller deployment include the following: For small site, remote office, or SBC deployments that carry low traffic, use a single Cisco router with integrated services such as CUBE, MTP, VoiceXML, firewall, and SRST features. For larger site, campus, data center or SBC deployments that carry high traffic, use a dedicated router for CUBE and other dedicated routers for MTP or VoiceXML or any other service you might need at that site. Pay careful attention to performance engineering of SIP trunks into your network because they most likely change the call flow and the bandwidth allocation to calls. Whether you use H.323-SIP or SIP-SIP on CUBE makes no difference to its ses- sion capacity. DTMF interworking or delayed offer to early offer adds no significant extra load to CUBE. Using SIP profiles for normalization on CUBE can have a performance effect depending on the number and complexity of the rules. Configuring MTPs on the same platform as CUBE or using transcoding are CPU- intensive tasks and must be carefully engineered. If you use CUBE platforms te