NGN
IMS Based Architecture

The initiative of organization institutions 3GPP within the specifications of UMTS (Universal Mobile Telecommunications System) architecture (3GPP within the UMTS architecture 5/6) has defined two domains:

The packet switching domain extends the existing GSM network and other mobile 2nd generation (2G) networks by the CDMA-based access, while the packet switching domain extends the abilities of the GPRS and other systems of 2.5 generation.

The subsystem for supporting multimedia services, telephony and IP-based message sending, designed in the framework of the packet switching domain is called IMS (IP Multimedia Subsystem). IMS is based on the IP architecture for multimedia and it was placed as a supporting network element to provide standardized and universal services for mobile users. As it was one of the first concepts on which all the standardizations institutions agreed and which conformed to the NGN principles, it is becoming one of the reference concepts for the fixed networks as well.

The 3GPP adopted SIP (Session Initiation Protocol) [7], which was originally standardized by the IETF. In time, the 3GPP discovered that there were gaps between the SIP, as initially defined by the IETF, and the features that were required to provide full support for IMS networks. Because SIP did not address all the requirements of IMS networks, the 3GPP subsequently defined dozens of new SIP extensions that are specific to IMS networks, e.g. [8]. Collectively, these extensions comprise the IMS SIP protocol, which is defined in the 3GPP TS.24.229 standard. IMS SIP extensions, such as extended call control, presence and instant messaging, extend the functionality of SIP on IMS networks.

By definition, SIP is not a protocol designed for a specific network or application. To use SIP, you can define the usage profile. Usage profiles work much like templates, and provide a varied, flexible environment for application development in which you can easily develop an application suited to your particular requirements can be easily developed. In effect, this is what IMS SIP did. The IMS SIP usage profile is the most important in the telecommunications industry, as it affects the entire telecom industry and not only mobile networks. The usage profile used by IMS SIP is actually the most appropriate for NGN networks. There are numerous IMS SIP extensions. The figure below illustrates a typical IMS network. Note that all SIP interfaces are shown in orange and specify the name of the interface between two adjoining entities. For example, the AS uses the ISC interface.

SIP in IMS