By now a lot of people have heard about VoIP and making cheap phone calls on the “Net”. SIP is the underlying internet protocol that drives the VoIP revolution. But SIP is sooooo much more! Read about the power of SIP and what’s in store for you just around the corner!
SIP — Session Initiation Protocol –
SIP is promising because of its natural integration in the IP world, its evolutivity, and its flexibility. SIP is a key enabler for successful services such as instant messaging, as well as new services.
SIP has also been selected by the 3GPP (third generation partnership project) as a major component of IMS (IP Multimedia Subsystem) for the evolved UMTS core network.
What Is IMS?
IMS stands for IP Multimedia Subsystem, a concept developed and specified by the 3rd Generation Partnership Project (3GPP). 3GPP is a collaboration agreement established in December 1998 among various standards bodies, currently (March 2005) comprising:
- Alliance for Telecommunications Industry Solutions (ATIS)
- Association of Radio Industries and Businesses (ARIB)
- China Communications Standards Association (CCSA)
- European Telecommunications Standards Institute (ETSI)
- Telecommunications Technology Association (TTA)
- Telecommunication Technology Committee
The original aim of 3GPP was to specify a third-generation mobile system based on evolved GSM core networks and the radio access technologies they support, but this was subsequently extended to include the maintenance and development of the GSM technical specifications and technical reports, including evolved radio access technologies. IMS is a result of this program.
IMS increases the functionality of packet-switched mobile networks (such as 3G GSM) by supporting IP-based applications and services through the SIP protocol. However, the rapid spread of fixed-network broadband and the offering of services such as transactions, content distribution, and VOIP over all-IP networks have made IMS increasingly relevant to fixed operators as well.
Effectively, IMS provides a unified architecture that supports a wide range of IP-based services over both packet- and circuit-switched networks, employing a range of different wireless and fixed access technologies. A user could, for example, pay for and download a video clip to a chosen mobile or fixed device and subsequently use some of this material to create a multimedia message for delivery to friends on many different networks. A single IMS presence-and-availability engine could track a user’s presence and availability across mobile, fixed, and broadband networks, or a user could maintain a single integrated contact list for all types of communications.
A key point of IMS is that it is intended as an open-systems architecture: Services are created and delivered by a wide range of highly distributed systems (real-time and non-real-time, possibly owned by different parties) cooperating with each other. It is a different approach to the more traditional telco architecture of a set of specific network elements implemented as a single telco-controlled infrastructure.
Why Is It Important?
IMS is potentially the base of a new telecom business model for both fixed and mobile networks and is a key enabler of fixed/mobile convergence. In principle it replaces the traditional walled-garden approach of a single operator, offering a limited range of services from within a highly controlled network, with an almost limitless range of highly functional services that span multiple operator and service-provider domains – fixed and mobile.
Obviously, technical potential and industry politics frequently collide, and IMS is not necessarily going to create an open-service Nirvana overnight. During the standard’s development there was a strong desire to perpetuate the mobile walled-garden approach, while allowing third-party developers to contribute applications and application segments. 3GPP was very anxious for mobile service providers not to end up as bit-pipe suppliers.
Nevertheless, it’s the fixed and mobile aspect that has got many in the industry so excited. A virtuous circle has emerged in which developments that began in the wireline environment with IP and SIP were picked up by 3G standards developers, refined and extended, and now are being fed back to the wireline community. IMS may have been designed for 3G, but now it’s much more than that, and everyone is converging on the same basic platform: IMS.
Key attractions of IMS are:
- Access independence: IMS will eventually work with any network (fixed or mobile) with packet-switching functions, such as CDMA2000, GPRS, UMTS, and WLAN (this in the future Release 6). Open interfaces between control and service layers allow elements and calls/sessions from different access networks to be mixed.
- Different network architectures: IMS allows operators and service providers to use different underlying network architectures. For example, access can be tightly coupled to the operator’s network or employ a third-party IP network as a looser intermediary.
- Terminal and user mobility: The mobile network provides terminal mobility, while user mobility is provided by IMS and SIP.
- Extensive IP-based services: IMS should make it easier to offer just about any IP-based service. Examples include voice over IP (VOIP), push-to-talk over cellular (POC), multiparty gaming, video/audio conferencing, and content sharing.
