 considered viable for customers in the long term. SP Network-Enhanced Services To differentiate their offerings, SPs try to offer services on their SIP trunks that are beyond basic PSTN replacement. These advanced services often require some type of enhanced service servers and infrastructure. These devices can either be logical entities that are co-resident on the same physical hardware as the call agent or other servers of the SP, or they might be distinct and separate both physical and logical devices. Generally, as SPs scale their services, enhanced services are deployed on dedicated hardware to enable the SP to optimize the deployment of servers to match their customer profiles. The specific roles that enhanced services servers provide to SPs that deploy a SIP trunk service vary widely depending on the service offered. Typically, the service is offered such that the SP call agent can provide the basic functionality, but the SP can sell an addi- tional service that might be provisioned on the enhanced services servers. Some examples of services include Fixed Mobile Convergence (FMC) services: SP offers this on top of the SIP trunk that enables for the intelligent routing of calls to both cellular and fixed locations. Network-provided voicemail services: A service that SP offers that provides a hosted voicemail service. In this case, when a call exceeds the maximum number of ring attempts, instead of being forwarded to a local voicemail solution, it is forwarded across the SIP trunk to a network-based voicemail solution. Video calling services: Enables an SP to intelligently route calls to endpoints such as those that support the capabilities of video calls are routed to special equipment. This service is often done to support either high-end video, such as Telepresence video calls over SIP trunks, or in combination to FMC services to connect fixed-line SIP video calls to cellular network video calls. Chapter 5: Components of SIP Trunks 71 These are just a few of the many possible enhanced functions or servic