IMS (The Internet protocol (IP) Multimedia Subsystem) is an architectural framework designed to facilitate IP multimedia services based on SIP (Session Initiation Protocol) which is a session control protocol for IP based networks to facilitate both voice and multimedia services. Since IMS use SIP as its main signaling protocol it has been able to integrate with a lot of platforms, such as internet. The main reason for IMS to choose SIP is to meet many IMS requirements, and it is considered as flexible and secure.
IMS
IMS was originally created specifically for mobile applications by the 3GPP and 3GPP2. However, nowadays it is very popular and widespread among the fixed line providers, since they are being forced to find ways of integrating mobile associated technologies into their networks. IMS mainly enables the convergence of data, speech, and mobile network technology over IP based infrastructure, and it provides the necessary IMS capabilities such as service control, security functions (e.g. authentication, authorization), routing, registration, charging, SIP compression, and QOS support.
IMS can be analyzed with its layered architecture which includes many layers with different functionalities. This architecture has enabled the reusability of service enablers and many other common functions for multiple applications. The responsibility of the first layer is to translate the bearer and signaling channels, from legacy circuit switch based networks to packet based streams and controls. The functionality of the second layer is to provide elementary level media functions to the higher level applications. Moreover, IMS has allowed other third parties to take control of call sessions and access subscriber preferences, by using higher level of application services and API gateways.
The IMS architecture gives service providers the opportunity to deliver new and better services, with reduced operating costs, across wired, wireless, and broadband networks. Most of the applications supported by the Session Initiation Protocol (SIP) have been unified by IMS in order to ensure the proper interaction between legacy telephony services with other non telephony services such as, instant messaging, multimedia messaging, push-to-talk, and video streaming.
SIP
SIP is a session control protocol which resides in the application layer and can perform multimedia session establishment, modification and tear down in real time communications over IP based networks. SIP was originally developed by the Internet Engineering Task Force (IETF) together with many leaders in the industry.
In managing sessions, SIP can invite participants to sessions that already exist such as multicast conferences. Media of the already existing session can be added or removed in real time. SIP also support for the implementation of ISDN and Intelligent Network telephony subscriber services with transparently supporting name mapping and redirection services, which also contribute to enable the personal mobility. This is defined as the ability of end-users to originate and receive calls while being able to be located by the network as they move, access different switching areas, fully accessing subscribed telecommunication services on any terminal in any location.
Generally SIP devices communicate with each other using SIP servers which provide an infrastructure for routing, registration, and authentication and authorization services. SIP cannot exist alone in a communications system. So it is rather used as a component with other IETF protocols in order to build a complete multimedia architecture. These consist of various protocols such as RSTP (Real Time Streaming Protocol), MEGACO (Media Gateway Control Protocol), SDP (Session Distribution Protocol), etc. SIP supports both IPv4 and IPv6; thus it’s very popular among many users.
What is the difference between IMS and SIP?
- SIP is just a signaling protocol whereas IMS is one large architecture consisting of a combination of services at a higher level. In addition, SIP and many other protocols are used as parts of the entire architecture.
- Both IMS and SIP based network systems are reliable and are suitable for small and moderate business usage.
- Both of the IMS and SIP based network systems are able to handle these many users
- SIP supports VoIP, but IMS supports a range of services other than VoIP. Thus, it is considered as the next evolution of Media on IP.