ions are based on the following design goals: 1. The design should be scalable in the long term and should not be constrained by transi- tional designs. 2. The platform is a shared infrastructure supporting multiple services on a shared core. 3. There are well-defined and limited interfaces to client service infrastructures, such as SBCs, ASs, OSSs, and other shared elements and services. 4. The design must meet carrier-grade requirements of five 9 S (99.999%) availability. 5. Geo-redundancy is required. 6. The design needs to allow operations to easily maintain and troubleshoot failures and must include design for audit tools, call trace probes, backup/restore, console server, jumpstart/ kickstart, and software upgrade servers. 7. Minimal configuration changes should be required for growth of components. As shown in Figure 14.13, the IMS service platforms follow a layered architecture. The AS layer contains various ASs that support voice and multimedia services. Below are some of the ASs supported: CPM-converged IP messaging server; provides SMS-over-IP service. VoLTE AS-telephony AS; provides calling feature and specialized service logic in call processing for VoLTE. UCE AS-user capabilities exchange AS; enables users to discover service capabilities of the devices of their contacts, thereby enhancing communications. PCM AS-personal communication manager AS; provides access to call logs and other portal services. The core contains the session management and media network elements including CSCF-call session control function; the serving CSCF (S-CSCF) is the principal call pro- cessing element. When a user endpoint (UE) registers with the network, the UE is assigned to a particular S-CSCF. The interrogating CSCF (I-CSCF) is used for making queries Application IMS Service Platform Servers Components VoLTEAS ICSCF SCSCF ECSCF SCCAS Access A-SBC I-SBC FIGURE 14.13 IMS service platform layered architecture. Building the Network of the Future to the HSS, and for assigning the S-CSCF to the UE. The emergency CSCF (E-C