Mobile Networks Architecture

Chapter 6

The IMS Network

Mobile networks functioning in PS (Packet Service) mode solely carry out the transport of telephone signals (voice and signaling). Signaling processing, which provides the telephone service, is supplied by the IMS (IP Multimedia Subsystem), an entity outside the mobile network.

Section 6.1 explains the SIP (Session Initiation Protocol) that is used to register the user with the telephone service and to establish a session. The SDP (Session Description Protocol) connected to the SIP is used for media negotiation (voice, video and data).

Section 6.2 explains the IMS architecture, which consists of a set of functions in charge of SIP/SDP signaling and media processing. Signaling processing involves the control of the session and the routing of signaling messages. Media flow processing concerns functions that are unavailable in the mobile network, such as the conference and the gateways to the PSTN (Public Switched Telephone Network) fixed telephone networks and the PLMNs (Public Land Mobile Networks).

Section 6.3 describes the procedures concerning the user’s registration to the telephone service and the establishment of a session that includes the routing of requests and media negotiation. Media negotiation refers to the control and selection of the media and codec, control of access to the resource and the reservation of resources in the mobile network.

6.1. The SIP

Numerous protocols have been defined to support real-time multimedia data, such as voice, ...