or evaluation include the following list, and you can choose one or several of these for your implementation: Contact center calls (inbound, outbound, or both). Normal business calls but only for specific locations (for example, initially perhaps only for your campus sites and later for remote sites). Or perhaps cost benefits are accrued only if you use it for all sites. Chapter 6: SIP Trunking Models Call direction, for example, all inbound calls use the SIP trunk but not outbound calls. Or perhaps all incoming and outgoing calls from the campus site but only inbound calls for remote sites. Call type, for example, long-distance calls use the SIP trunk, but local calls remain on TDM trunks. Or perhaps all normal business calls from all sites use the SIP trunk, but fax and emergency calls remain on TDM trunks until a later phase of rollout. Tip Whichever call patterns you decide to use your SIP trunk for are likely to precipitate both call routing and dial-plan adjustments that affect both your network and your call agent configurations. Consider these carefully and coordinate these changes, or phases of changes, with installing a SIP trunk to various sites in your network. IP Addressing Centralized SIP trunking typically uses two publicly routable enterprise IP addresses to which the SP's session border controller points. Sometimes up to ten IP addresses can be available for a single logical SIP trunk. Few providers today use Domain Name System (DNS) for IP address resolution and redundancy or alternative destinations. If your SIP trunk provider is also your MPLS data network provider, the SIP trunk address space is more flexible and likely falls within your already allocated MPLS site address space. A distributed SIP trunking model is often most beneficial if your existing MPLS data provider offers this. In this case an IP address per remote site and security considerations are not hurdles to the installation of a multiple SIP trunks, and you can easily derive the many benefits of distributed trunking. If your S