t does not compromise voice quality. (After all, the promise of a SIP trunk is to improve PSTN services, not worsen them.) It also eases fax issues, obviates the need for transcoding at your SBC, and better positions you for new SIP trunk services that will almost certainly include increasingly bandwidth intensive applications such as high-fidelity wideband codecs and video. Although SIP is a standard protocol, it actually consists of a large number of individ- ual standards (Internet Engineering Task Force [IETF] Request for Comments [RFC]), and there are many optional components to these RFCs and alternative ways to imple- ment the same call flow. SIP interoperability is not mature enough that all applications Chapter 11: Deployment Steps and Best Practices 259 predictably interwork with other SIP applications, even though they all might be standards-compliant. This means you might need tools to normalize (that is, manipu- late) SIP messages as they flow through your network from your applications across the SIP trunk to the PSTN. Cisco Unified Communications Manager (CUCM) Best practices in the area of CUCM deployment include the following: Generally, the decision between using H.323 and SIP on CUCM depends on the fea- tures, your preference, protocol maturity, and the degree of interoperability between the applications you have in your network. CUCM 6.x or 7.x is recommended for SIP trunking, using a SIP-to-SIP configu- ration. If older versions of CUCM are used and cannot be upgraded to 6.x or 7.x, use H.323 trunking to the call agent and H.323-to-SIP conversion on your SBC. The recommended CUCM Configuration for SIP trunking includes Delayed offer (with no media termination point [MTP]) for Cisco UCM outbound calls Early offer (with no MTP) for CUCM inbound calls Use delayed offer to early offer interworking on your session border controller (CUBE) Avoid MTP designs if possible; if not, colocate the MTPs with your SBC (CUBE) to optimize the media path. Older releases of CUCM prefer higher bandwidth codecs t