Gonzalo Camarillo Per Synnergren

This chapter explains how the control plane of the Multimedia Telephony service works. The first part of the chapter explains the Session Initiation Protocol (SIP) that is used by the Multimedia Telephony clients and IMS to set up, modify and release the Multimedia Telephony sessions. SIP, together with the Session Description Protocol (SDP), is also used to realize supplementary services like communication diversion, conferencing and communication barring that are present in ISDN/PSTN. To exemplify the Multimedia Telephony session management procedures and the supported supplementary services a number of example flows are provided that describe how Multimedia Telephony sessions are set up, modified and released and how supplementary services are realized using SIP/SDP.

Quality of Service (QoS) is becoming increasingly important with larger volumes of traffic in the packet switched domain. The use of IMS as the service layer provides the possibility to negotiate QoS for the individual media components of the Multimedia Telephony sessions at session establishment as well as during the session. The IMS uses the UMTS bearer service provided by the 3GPP QoS architecture. This chapter describes the GPRS session management signaling and the policy control and charging architecture, which all are key components to enable QoS negotiation in IMS sessions.

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