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switched networks, a number of new protocols have been developed, namely BICC for
call control over a range of different bearer options and M3UA and SCTP for the transport
of SS7 signalling over the CS core. Release 4 is an important step in the evolution of
UMTS to using IP for all transport (R5 and beyond).




FURTHER READING

RFC 1305: Network Time Protocol (Version 3) Speci¬cation, Implementation. D. Mills.
March 1992.
RFC 1889: RTP: A Transport Protocol for Real-Time Applications. Audio-Video Transport
Working Group, H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson. January 1996.
RFC 1890: RTP Pro¬le for Audio and Video Conferences with Minimal Control. Audio-
Video Transport Working Group, H. Schulzrinne. January 1996.
RFC 2198: RTP Payload for Redundant Audio Data. C. Perkins, I. Kouvelas, O. Hod-
son, V. Hardman, M. Handley, J. C. Bolot, A. Vega-Garcia, S. Fosse-Parisis. Septem-
ber 1997.
RFC 2327: SDP: Session Description Protocol. M. Handley, V. Jacobson. April
RFC 2508: Compressing IP/UDP/RTP Headers for Low-Speed Serial Links. S. Casner,
V. Jacobson. February 1999.
RFC 2719: Framework Architecture for Signaling Transport. L. Ong, I. Rytina, M. Gar-
cia, H. Schwarzbauer, L. Coene, H. Lin, I. Juhasz, M. Holdrege, C. Sharp. October
1999.
RFC 2960: Stream Control Transmission Protocol. R. Stewart, Q. Xie, K. Morneault,
C. Sharp, H. Schwarzbauer, T. Taylor, I. Rytina, M. Kalla, L. Zhang, V. Paxson.
October 2000.
RFC 3015: Megaco Protocol Version 1.0. F. Cuervo, N. Greene, A. Rayhan, C. Huitema,
B. Rosen, J. Segers. November 2000.
RFC 3267: Real-Time Transport Protocol (RTP) Payload Format and File Storage Format
for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB)
Audio Codecs. J. Sjoberg, M. Westerlund, A. Lakaniemi, Q. Xie. June 2002.
RFC 3332: Signaling System 7 (SS7) Message Transfer Part 3 (MTP3) - User Adap-
tation Layer (M3UA). G. Sidebottom, Ed., K. Morneault, Ed., J. Pastor-Balbas, Ed.
September 2002.
RFC 3435: Media Gateway Control Protocol (MGCP) Version 1.0. F. Andreasen, B. Fos-
ter. January 2003.
3GPP TS23.153: Out of Band Transcoder Control; Stage 2.
3GPP TS23.205: Bearer-independent circuit-switched core network; Stage 2.
3GPP TS25.415: UTRAN Iu interface user plane protocols.
3GPP TS29.202: Signalling System No. 7 (SS7) signalling transport in core network;
Stage 3.
554 IP TELEPHONY FOR UMTS RELEASE 4


3GPP TS29.205: Application of Q.1900 series to bearer-independent circuit-switched core
network architecture; Stage 3.
3GPP TS29.232: Media Gateway Controller (MGC) “ Media Gateway (MGW) interface;
Stage 3.
3GPP TS29.414: Core network Nb data transport and transport signalling.
3GPP TS29.415: Core network Nb interface user plane protocols.
ITU-T Q.765.5: Application Transport Mechanism.
ITU-T Q.1902.1: Bearer Independent Call Control CS2 Functional Description
ITU-T Q.1902.2: Bearer Independent Call Control CS2 General Functions of Messages
and Signals.
ITU-T Q.1902.3: Bearer Independent Call Control CS2 Formats and Codes.
ITU-T Q.1902.4: Bearer Independent Call Control CS2 Basic Call Procedures.
ITU-T Q.1902.5: Exceptions to the Application Transport Mechanism in the Context of
Bearer Independent Call Control.
ITU-T Q.1902.5: Generic Signalling Procedures and Support of the ISDN User Part
Supplementary Services with the Bearer Independent Call Control Protocol.
ITU-T Q.1950 Call Bearer Control Protocol.
ITU-T Q.2630.1-2: AAL type 2 signalling protocol.
ITU-T Q.1990 BICC tunnelling control protocol.
ITU-T Q.1970 IP Bearer Control protocol.
ITU-T Q.1912.1 ISUP-BICC Interworking.
ITU-T Q.1912.2 Interworking between selected Signalling System (PSTN Access DSS1,
C5, R1, R2, TUP) AND THE Bearer Independent Call Control Protocol.
ITU-T Q.2150.0 Generic Signalling Transport Service.
ITU-T Q.2150.1 Signalling Transport Converter MTP and MTP3 B.
ITU-T Recommendation Q.2150.3 Signalling Transport Converter on SCTP.
ITU-T H.248: Media Gateway Control Protocol (06/00).
A list of the current versions of the speci¬cations can be found at http://www.3gpp.org/
specs/web-table specs-with-titles-and-latest-versions.htm, and the 3GPP ftp site for the
individual speci¬cation documents is http://www.3gpp.org/ftp/Specs/latest/
9
Release 5 and Beyond (All-IP)


9.1 INTRODUCTION
Release 5 (R5) builds on the partial implementation of Internet protocol (IP) packet switch-
ing within the core network, as discussed thus far, to move to an all-IP architecture. In
this release, packets can be moved end-to-end using IP transport with an enhanced general
packet radio service (GPRS) network connected to an IP multimedia subsystem (IMS).
The GPRS backbone for R5 must be able to provide similar levels and classi¬cations
of quality of service (QoS) usually associated with asynchronous transfer mode (ATM)
networks. This is to allow for the delivery of time-sensitive traf¬c such as voice and mul-
timedia. As well as enhancements to the core network, the radio access network (RAN)
also migrates from ATM to IP. Even though the vision for R5 is for a total IP solution,
the operator may well still use ATM as a transport solution for some parts of the network.
This is possible because all UMTS releases must provide backward compatibility with
earlier releases. Figure 9.1 shows the architecture of the R5 network.
Notice that in the R5 network, the circuit switched (CS) domain can be dispensed with
since the services associated with it, such as transfer of voice traf¬c, can be carried over
the GPRS and IMS networks using IP QoS mechanisms. That given, many operators
may still be using the R4 CS domain as well as the R5 IMS architecture. This allows
for a gradual migration to an all-IP architecture with the minimal disruption to service.
Some voice calls may be handled using the CS domain and some, for example video call
services, via the IMS. The hybrid con¬guration is shown in Figure 9.2.
The major new components of the Release 5 architecture are now described.


9.2 IP MULTIMEDIA SUBSYSTEM (IMS)
R5 introduces a new network domain called the IP multimedia subsystem (IMS). This is
an IP network domain designed to provide appropriate support for real-time multimedia
services. Figure 9.3 shows the connections between the IMS and other networks.

Convergence Technologies for 3G Networks: IP, UMTS, EGPRS and ATM J. Bannister, P. Mather and S. Coope
™ 2004 John Wiley & Sons, Ltd ISBN: 0-470-86091-X
556 RELEASE 5 AND BEYOND (ALL-IP)



PSTN/
ISDN/
CSPDN
RAN

HSS

IP
IMS
Backbone
UE
SGSN GGSN
RNC
WBTS
Packet Core
Uu Iu
IP Network




Figure 9.1 UMTS R5 network

Circuit Core

PSTN/ISDN/
MSC Server/VLR CSPDN
RAN

MGW
MGW
IMS
UE HSS
RNC
WBTS
IP
Uu Iu Backbone Data Network
e.g. Internet
SGSN GGSN
Packet Core

Figure 9.2 R4 to R5 migration

The user equipment (UE) communicates with the IMS using GPRS, with the IMS being
directly connected to the GGSN. The IMS provides services to mobile users such as:

• real-time communication using voice, video or multimedia messaging (i.e. voice and
video telephony);
• audioconferencing and videoconferencing;
• content delivery services such as video, audio or multimedia download;
• content streaming services such as video, audio or multimedia streaming (e.g. using
video on demand server);
• multimedia messaging service (MMS).

Each operator™s IMS can be connected to other operators™ IMSs, allowing multimedia
services between users on different networks. Connections to the public Internet allow
9.2 IP MULTIMEDIA SUBSYSTEM (IMS) 557



Operator
A Softswitch

Video on
MMS server
demand server ISDN
GGSN
IMS MGW

Firewall
Conferencing
bridge
Firewall
HSS(A)



Internet
Firewall
Operator
B
Operator
Video on B
demand server
GGSN IMS

MMS server Conferencing
bridge
HSS(B)


Figure 9.3 IMS connection


MMS messaging as well as voice over IP (VoIP) and video telephony between mobile and
¬xed-line users. Finally, the interface to the ISDN (or other circuit switched networks)
allows VoIP calls to be connected through to conventional ¬xed-line and mobile users,
e.g. global system for mobile communications (GSM). Connections between the IMS and
other IP networks are controlled by ¬rewalls to protect against hacking. The interface
between the IMS and the CS network is controlled by the softswitch and media gateway
(MGW) components. Within the operator™s network the IMS is connected to the home
subscriber server (HSS) to allow for subscriber authentication, authorization and mobility
management. For R5 and beyond, the IMS can be used to provide transport for all of the
operator™s services, including conventional voice calls.
Figure 9.4 shows a functional diagram of the IMS. The dotted lines correspond to
signalling paths and the solid lines to user data transport.
The IMS is made up of a number of component parts connected together using an IP
backbone. This is implemented as a separate network from the IP backbone connecting
the serving GPRS support node (SGSN) and the gateway GPRS support node (GGSN)
for such purposes as security. Each mobile user must ¬rst obtain a GPRS connection
(i.e. a packet data protocol (PDP) context) to the IMS prior to using its services, which
558 RELEASE 5 AND BEYOND (ALL-IP)


HSS
Other operator's
IMS networks

Home/visited Home IMS
IMS
Firewall MRF
MRFC
S-CSCF


MRFP
P-CSCF
MGW
I-CSCF
GGSN

PSTN
Signalling
gateway
BGCF

Application MGCF
Server AS


Figure 9.4 IMS functional diagram


means authentication/registration is done twice, ¬rst for GPRS and then for IMS. The UE
always connects to the IMS via the proxy call session control function (P-CSCF), which
may reside at the user™s home network or in a roaming scenario within a visited network.
On the right-hand side of the ¬gure can be seen the connection to external CS networks
via the MGW and media gateway control function (MGCF) (softswitch). The application
server provides IMS value-added services. This could be, for example, a content server
(video on demand) or an interactive voice/video mailbox server. The interrogating call
session control function (I-CSCF) connects this network to other IMS networks. It acts
as a point of entry for call signalling.
Each of the components shown in Figure 9.4 is a mandatory requirement with the
exception of the application server and the media resource function (MRF) (which is
only needed for conferencing applications). The components are de¬ned in the following
subsections.

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