Chapter 24 - Conferencing in the IMS pptx

Chapter 24

Conferencing in the IMS

In Chapter 23, we introduced the basic technologies and architectures developed by the IETF

in the conferencing area. In this chapter, we discuss how those technologies are used in

the IMS to provide a conferencing service. This chapter is fairly brief because applying the

technologies described in Chapter 23 to the IMS architecture is relatively straight-forward.

24.1 The IMS Conferencing Service

The IMS conferencing service (specified in 3GPP TS 24.147 [32]) is based on the SIPPING

conferencing framework (specified in RFC 4353 [272]). Of the specifications produced

within the XCON working group, the IMS conferencing service only uses BFCP (specified

in RFC 4582 [106]). In the future, as the work in the XCON working group progresses, the

IMS conferencing service may use the XCON framework and the conference control protocol

developed by the XCON working group. However, at present, they are not yet used in the

context of this IMS service.

The IMS conferencing services is based on the tightly-coupled conference model

described in Figure 23.3. In the IMS, the conference server is distributed into two logical

entities: one handling signaling and the other handling media, as shown in Figure 24.1. The

former corresponds to a combination of an AS and an MRFC; the latter corresponds to an

MRFP.

PSTN interworking is also part of the IMS conferencing service. Users on the PSTN can

participate in IMS conferences through an MGCF, which acts as a conference participant and

talks SIP to the AS/MRFC part of the conference server.

24.1.1 Creating and Joining a Conference

A client creates a conference at a server by sending an INVITE request (1) to the server’s

conference factory URI (defined in RFC 4579 [195]), as shown in Figure 24.2. The server

responds with a 200 (OK) response (2) that carries the new conference URI in its Contact

header field. Users joining the conference send INVITE requests (4) to this conference URI.

Therefore, the conference factory URI is only used at conference creation in order to obtain

a conference URI, which is allocated by the conference server. Once a conference is created,

it is identified by its conference URI.

ıa- ´ Martın´

The 3G IP Multimedia Subsystem (IMS): Merging the Internet and the Cellular Worlds Third Edition

Gonzalo Camarillo and Miguel A. Garc

Thư viện tri thức trực tuyến