Developing SIP and IP Multimedia Subsystem (IMS) Applications

28 Developing SIP and IP Multimedia Subsystem (IMS) Applications

2.1 IMS overview

IP Multimedia Subsystem (IMS) is a set of requirements and specifications

defined by 3rd Generation Partnership Project (3GPP) and 3rd Generation

Partnership Project 2 (3GPP2). 3GPP and 3GPP2 were formed through

collaboration agreements that include a number of regional telecommunication

standards bodies. IMS defines a unifying architecture for IP-based services over

both packet- and circuit-switched networks. It enables the convergence of

different wireless and fixed access technologies for the creation, delivery and

consumption of multimedia services. IMS also supports services integration

through standardized reference points (akin to interfaces and protocols) which

not only makes service creation faster and easier but also leverages the services

available through Internet technologies such as Web Services.

2.1.1 IMS vision and history

IMS is at the center of the 3G (third Generation) initiatives driven by 3GPP and

3GPP2 who are participants in International Mobile Telecommunications-2000

(IMT-2000) the global standard for third generation (3G) wireless

communications, defined by a set of interdependent International

Telecommunications Union (ITU) Recommendations.

The 3GPP was formed as a collaboration of many organizations (includes

Association of Radio Industries and Businesses, China Communications.

Standards Association, European Telecommunications Standards Institute,

Alliance for Telecommunications Industry Solutions, Telecommunications

Technology Association of South Korea and Telecommunication Technology

Committee of Japan) in 1998 to develop the technical specifications for a 3G

network evolving from a GSM network. A similar charter, 3GPP2 (includes

Association of Radio Industries and Businesses, Telecommunication Technology

Committee of Japan, China Communications. Standards Association,

Telecommunications Technology Association of South Korea and

Telecommunications Industry Association), was formed to evolve the North

American and Asian networks from traditional CDMA2000 networks into a 3G

platform.

Both 3GPP and 3GPP2 conceptualized their respective IMS (IP Multimedia

Subsystem) architectures to support packet switched communication, in order to

merge the Internet and the cellular worlds. The IMS core network has a common

IP based transport and signalling, which can be accessed by different networks.

IMS common signalling is based on SIP. We presented an overview of SIP in

Chapter 1, “Introduction to Session Initiation Protocol (SIP)” on page 3 as an

end-to-end based session management control protocol. SIP allow applications

Chapter 2. Introduction to IP Multimedia Subsystem 29

to remain agnostic of the access network, which matches the network access

requirements for IMS.

Initial concepts for IMS emerged with the Universal Mobile Telecommunications

System (UMTS) third-generation (3G) specifications in 1998. The first

specification of IMS was published in March of 2003 by 3GPP in UMTS Release

5. UMTS Release 5 provided general description of IMS, SIP and end-to-end

Quality of Service (QoS) as part of an “All IP” network. IMS continues to evolve

with each UMTS release since 2003. New functions and changes to IMS are

introduced through 3GPP approved change requests (CRs) with each release.

3GPP release 6 and 7 added interworking with wireless local area networks

(WLAN) and support for fixed networks, by working together with TISPAN

(Telecoms & Internet converged Services & Protocols for Advanced Networks).

The vision of IMS as the common platform for development and delivery of

diverse multimedia services for a true mobile Internet is based on the set of

requirements set forth in the 3GPP IMS requirements captured in 3GPP TS

22.228.

Available at:

http://www.3gpp.org/ftp/Specs/html-info/22228.htm

The following are the highlights of the key IMS requirements:

 IP multimedia sessions

IP multimedia session requirements are focused on the main service

delivered by IMS, it includes support for a variety of media (such as voice,

video and data) and one or more applications that provide the service

experience within sessions. The IP multimedia session requirements call for

media interoperability and per user application flow control.

 Quality of Service (QoS)

IMS QoS characteristics are negotiated between end points in IMS sessions.

The parameters include the type of media, the codecs and encoding formats,

bandwidth, delay, delay variation and packet loss. The IMS QoS requirements

include negotiations at session establishment and during the session as well

as for individual media components. IMS requirements also allow for

operators to set policy and control QoS for all or individual users.

Note: Telecoms & Internet converged Services & Protocols for Advanced

Networks (TISPAN) is a standardization body that is working through the

European Telecommunications Standards Institute (ETSI) to define the Next

Generation Network architecture. Some aspects of the TISPAN Release 1

architecture is based on IMS.