Evolved Packet System (EPS): The LTE and SAE Evolution of 3G UMTS

4.4 IMS Protocols

The aim of this section is to briefly describe the main application protocols used by IMS (IP Multimedia Subsystem). All of these protocols have been defined by the IETF (Internet Engineering Task Force), which is the international community dedicated to the evolution of the Internet. Because they were designed in the scope of wired Internet communication session setup, 3GPP had to adapt them to specific IMS architectures and requirements. However, re-using worldwide standards for packet-based services within IMS has major advantages:

• The development cycle for terminals and network nodes is reduced as IMS based applications development only require adaptations to protocol stacks that already exist
• The inter-working between other packet networks is easier, as IETF application protocols are now widely used in public and private networks.

The rest of this section describes the following:

• SIP (Session Initiation Protocol), which is the protocol for packet session control (establishment, modification and termination).
• SDP (Session Description Protocol), which is the standard for describing and negotiating media components.
• RTP (Real Time Protocol), being the transport stack used by real-time sensitive packet-based services.

The intention here is not to provide an extensive view of IETF protocols, but rather to give an overview of the main characteristics (the main concepts and principles) and describe how they fit with the other elements of evolved UMTS architecture. ...