IMS uses several key elements to gain advantages such as mobility management, service quality, service control, and developer interfaces:
Home Subscriber Service (HSS) provides data storage for subscriber and service-related data including user identities, registration information, access parameters, and service-triggering information.
Call Session Control Function consists of several "sub-elements" that handle all of the signaling associated with call setup and teardown and basic SIP message exchange.
Security Gateway tunnels traffic between different carrier networks and between an enterprise and a carrier network. It primarily allows communication through NAT servers and firewalls, and may do other security functions such as packet filtering.
IP Media Server controls all of the media streaming functionality for rich multimedia messages: video, voice, and text. It handles associated coders (encoding/decoding) and transcoding media streams along with echo cancellation, tone detection, and tone generation.
Application Servers provide multimedia services to the IMS network by providing access to all other IMS elements as SIP servlets. New services are also deployed through the application servers, and since IMS has a modular architecture, only the application servers need to be replaced or upgraded when new services are deployed.
A modular platform architecture based on AdvancedTCA* addresses these specific requirements for IMS elements: high availability, SIP performance, rich media content and transcoding, video encoding and RTP acceleration, signaling, storage, in-memory database, control and user data separation, and privacy and security - TLS, SSL.
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