The document provides an overview of the IP Multimedia Subsystem (IMS) architecture, protocols, and services. Key points include: - IMS provides an integrated architecture for multimedia services over different access networks through the use of IP. - It allows for person-to-person and person-to-content communications using voice, text, pictures and video on both wireless and fixed networks. - The IMS architecture includes the Call Session Control Function (CSCF), Home Subscriber Services (HSS), Application Servers, and other network elements that provide services like authentication, authorization, charging and quality of service. - IMS supports multimedia applications and services like presence, instant messaging, push-

1. IMS – IP Multimedia Subsystem Architecture, Protocols and Services Waldir R Pires Jr Siemens Manaus 2005.06.21

4. Stove pipe architecture horizontal architecture

9. IMS Architecture Legacy Service Control Points Caller ID, Local number portability and 800 services. Application Servers IMS Applications OSA – GW (Open Service Access Gateway) inter-working between SIP and APIs for communication services It allows applications to access presence and call state information, application registration and resource management in the network Non-Telephony Services outside the telephony call model, such as Instant Messaging, Push To Talk and presence enabled TAS (Telephony Application Server) back-to-back SIP user agent that maintains the call state provides the basic call processing services including digit analysis, routing, call setup, call waiting, call forwarding, conferencing, etc. IM-SSF (IP Multimedia Services Switching Function) Provides the interworking of the SIP message to the corresponding CAMEL, ANSI-41, INAP or (TCAP) messages, services such as calling name, 800 services, etc. HSS (Home Subscriber Services) A database that maintains the unique service profile for each end user. This includes an end user’s current registration information (i.e., IP address), roaming information, telephony services (i.e., call forwarding information), instant messaging service information (i.e., buddies list), voice mail box options (i.e., greetings), etc. CSCF (Call Session Control Function) It provides the registration of the endpoints and routing of the SIP signaling messages to the appropriate application server. The CSCF interworks with the transport and endpoint layer to guarantee QoS across all services. In some IMS proposals, the CSCF is divided into Serving, Proxy and Interrogating CSCFs. MRCF – Media Resource Control Function It interworks the SIP signaling with the signaling used by the media servers. It also manages the distribution of sessions across multiple media servers. It is considered to be the central unit for media processing (transcoding, conferencing, TTS, etc.), MGCF – Media Gateway Control Function It interworks the SIP signaling with the signaling used by the media gateway (i.e., H.248). Media Server Responsible for the processing and generation of multimedia data, such as playing of announcements (audio/video), multimedia conferencing (e.g. mixing of audio), text to speech conversation (TTS) and speech recognition and realtime transcoding of multimedia data (i.e. conversion between different formats). Media Gateway It terminates voice data from a switched network (PSTN) and media (RTP) streams from packet switched network (Internet). It also acts as relays for multimedia streams i.o. end-2-end connections. Other functions include transcoding, echo cancellation and packet loss handling

14. IMS Services/Application Architecture

15. IMS Horizontal Architecture

19. IMS Summary Horizontal architecture to services and applications Common services and roaming discovery Interoperability, charging, roaming control for the operator Combination of voice, video and data Access convergence GPRS, cdma2000, WLAN, fixed network, etc. Enabler to a true 3G IP convergence