Ims whitepaper

White Paper

IMS Simplified: The Evolution of the SIP Client
Introduction
Flexibility has been a well-known attribute of the session initiation protocol (SIP). SIP is at the heart of the IP multimedia subsystem (IMS), exemplifying the extensibility of the SIP protocol. This paper provides a general discussion of the SIP protocol and highlights the differences between pure SIP clients and IMSclients. Many books and white papers have been written about SIP and IMS, yet it is difficult to find a source of information that clearly identifies the differences between a SIP client and an IMS client. This paper was created out of the common desire among the authors to provide a simplified view of SIP/IMS clients and to point the reader to the appropriate specifications for more detailedresearch. SIP was originally implemented for voice over internet protocol (VoIP) applications, initially for residential and now for businesses. SIP has become the accepted signaling for VoIP, although SIP clients and Proxies can contain certain liberties of the standards that might create issues when using different SIP implementations. This first phase of SIP for VoIP was a solid design, stablein requirements, but fairly simple in nature. Today, there is a new game in town that has thrust SIP into warp speed. That technology is IMS. SIP was always designed to be more then just a vehicle for VoIP, and IMS will put that to the test. Standards bodies are moving very fast to modify and extend standards for IMS. Since IMS is simply an architecture, the real winners are the applicationsrunning over the IMS architecture. Progress will move quickly as new applications will drive new requirements on SIP clients. This paper will examine what new requirements will be placed on a SIP client. Because of the nature of IMS, SIP client changes will go beyond SIP. This paper will review the areas of changes that will affect the SIP client and will discuss: 1. SIP Extensions, 2. Signalingcompression, 3. Security, 4. ENUM, and 5. Firewall/NAT traversal.

Written by: Jay Stewart Director of Corporate IMS Strategy JDSU Barry Constantine Principal Member Technical Staff JDSU Lincoln Lavoie Senior Engineer University of New Hampshire InterOperability Lab

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WhitePaper: IMS Simplified: The Evolution of the SIP Client

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2.0 Standards bodies driving IMS
There are standards bodies for all facets of telecommunications and data communications. For IMS to span all technologies and networks, it is important to understand the broad range of standards that govern IMS. The first standards body that greatly influences IMS is the International TelecommunicationUnion (ITU). The ITU created International Mobile Telecommunications-2000 (IMT-2000) which is the global standard for a 3G network—a collaboration of standards bodies make up the IMT-2000. Inside the IMT-2000 are two standards bodies that are the main focus for IMS: Third Generation Partnership Project (3GPP) and 3GPP2. 3GPP deals with UMTS networks and 3GPP2 deals with code division multipleaccess (CDMA) networks. Both have created standards for IMS, but most will refer to the 3GPP standards. 3GPP introduced packet switched voice services in a standard called R4. IMS was introduced in standards R5/R6. In R5, the standard calls for the use of SIP and IP as the basis for IMS, and this is where the Internet Engineering Task Force (IETF) comes in to play. IETF is responsible for SIP andother IP protocols. While SIP is a powerful protocol, it needed to be extended to fit the 3GPP needs. 3GPP and IETF started working on extending the standards for SIP into the requirements for IMS. In parallel, other groups such as CableLabs (cable company standards) started defining IMS support in data over cable services interface specification (DOCSIS) 2.0. Wireline groups such as the European...