al situations might exist in your net- work: Older versions of Cisco Unified Communications Manager (CUCM) capable of only H.323 Newer versions of CUCM that can reasonably be deployed with SIP Older IP-PBXs not capable of SIP without potentially expensive upgrades Newer SIP applications such as meeting servers, voice mail servers, and presence servers A shared SIP trunk for PSTN access used by all these applications SIP SP H.323 Presence H.323 Server H.323 H.323 Voice Mail Meeting Server Cisco Unified Cisco Unified IP-PBX SIP Applications Communications Communications Manager 4.x and 5.x Manager 6.x or Later Figure 8-1 H.323 and SIP Networks in Transition To interconnect these various H.323 and SIP applications, a border element can help by doing protocol translation of H.323 to SIP, or to normalize between different variations of SIP, and can also enable for the SIP trunk to the PSTN to be shared among these applications. SIP Normalization is discussed in more detail in the later "SIP Normalization" section in this chapter, but other areas of H.323 and SIP protocol interworking to consider include H.323 slow-start and fast-start and SIP delayed offer (DO) and early offer (EO). SIP DO means no session description protocol (SDP) information specifying the session attrib- utes such as codec choice is included in the initial INVITE for the call setup. SIP EO means an SDP is included in the initial call setup INVITE. The Cisco Unified Border Element (CUBE) supports the protocol conversion combinations given in Table 8-1. Endpoints Similar to applications, you can find a large variety of SIP endpoints on the market with widely varying capabilities. As you start to deploy these in your network, they also might give rise to a need to normalize SIP messaging across the enterprise to ensure interoper- ability or predictability (for example, of the information included in various SIP headers that control how phone displays are rendered). Service Provider SIP Trunk Interworking-SP UNI IP access from a service provider almos