IP for 3G - (P4)

Multimedia Service Support and Session ManagementTwo of the key new features of 3G networks are their ability to support multimedia applications and the Virtual Home Environment. The former implies a network with the ability to support more than just voice communications (and more than just non-real-time, data applications like the World Wide Web and e-mail).
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IP for 3G - (P4) IP for 3G: Networking Technologies for Mobile Communications Authored by Dave Wisely, Phil Eardley, Louise Burness Copyright q 2002 John Wiley & Sons, Ltd ISBNs: 0-471-48697-3 (Hardback); 0-470-84779-4 (Electronic) 4 Multimedia Service Support and Session Management4.1 Introduction Two of the key new features of 3G networks are their ability to support multimedia applications and the Virtual Home Environment. The former implies a network with the ability to support more than just voice commu- nications (and more than just non-real-time, data applications like the World Wide Web and e-mail). The latter is where users of 3G networks store their preferences and data. In its original sense, as described in Chapter 2, the VHE is responsible for tailoring the communications to the physical connec- tion and terminal currently being used. This chapter considers how this type of functionality could be provided in an IP network. It begins with a discus- sion of the key concept of session management. A multimedia communica- tion, such as a video-telephony call, is referred to as a session. There are a number of different functions that are required to provide and support sessions. This chapter focuses particularly on the session management control plane functions. Other aspects of session management (the data plane) are introduced in the first section but are discussed further within Chapter 6. Following this, we briefly consider how currently sessions and VHE functionality are handled in both 2G/R99 UMTS systems and the Inter- net. Within the Internet, control plane session management for real-time, multimedia services is an area that is still under development. The two main protocols for this role are reviewed. H.323 is currently in use today, whereas the Session Initiation Protocol (SIP) is a newer IETF standard. SIP is included in the next generation of UMTS standards. Its operation is then examined in some detail. The chapter then goes on to look at some examples of the power of SIP, how it could be put to use in 3G networks, in particular, how it can be used to link between traditional telephony networks and IP networks, and how SIP can enable advanced networking services. Throughout this chapter, SIP is considered in the context of a future, mobile, multimedia Internet. The use of SIP in forthcoming versions of UMTS is rather different to this model – 122 MULTIMEDIA SERVICE SUPPORT AND SESSION MANAGEMENT the 3GPP additions to SIP make it almost an entirely new protocol altogether. This is discussed further in Chapter 7. As SIP becomes better understood, it will become clear that, in addition to its role in multimedia service support, SIP is highly related to the original VHE concept.4.2 Session Management4.2.1 What is a Session? A session is a series of meaningful communications between two or more end points. Sessions are supported by connections 1 (such as a TCP /IP connection) that provide the physical connectivity, which ensures that bits flow correctly between the end points. The session provides the additional support that enables the receiver(s) to determine whether a particular stream of bits should actually be transformed into an audio-stream, for example. A session may have many connections associated with it. An example of this is a video conference, where the audio and video parts of the data are sent over separate connections. Further, a single connection may remain active through the lifetime of several sessions.4.2.2 Functions of Session Management Protocols Session-layer (signalling) protocols are used for creating, modifying, moni- toring, and terminating sessions with one or more participants. These sessions include multimedia conferences and Internet telephone calls. To illustrate this, consider a typical procedure that would have been required to establish an Internet Voice Call more than 7 years ago, running between two users at adjacent desks. The two users would first ensure that they would both be using the same application, agreeing on the nature of the voice coding, sampling rate, data compression, and error coding that would be used. IP addresses would be exchanged, and UDP may have been agreed on as the transport control mechanism, so that the connection could be established. At this point the users would stop talking and actually boot up their computers. Today, this entire process is part of ‘Session Initiation’ or ‘the control plane of session management’, and a number of different protocols exist to facilitate this process. This process is studied in depth in this chapter. Typically, on a first attempt at an IP voice call, speech would be very distorted because other traffic on the local Ethernet would be causing severe, variable, packet delays. Packet delay is very important for any 1 ‘Session’ is a highly generic term and is used in different ways in different communities – for example, the term ‘connect ...