Side_1_360

classes will be described as well as aspects con-
cerning QoS support over the radio interface,
handover issues and interworking with legacy
mobile systems. Chapter 4 gives a status over-
view of the end-to-end capabilities in UMTS
including the policy framework and IP layer
functionality to negotiate end-to-end QoS. To
conclude we give a summary of the matters dis-
cussed and point out some remaining open stan-
dardisation issues.

2 UMTS Architecture Overview

UMTS has been standardised in phases. The ini-
tial release (R99) includes the basic functionality
to access IP networks and the circuit switched
networks. The Core network part is composed
of a packet domain based on the GPRS architec-
ture and a circuit domain based on the GSM
architecture. The radio network (UTRAN) is
based on the W-CDMA technology and is func-
tionally independent from the core network. Its
function is to provide access to the core network
domains via the Iu interface. Further releases
add features to this basic functionality set.
Release 5 introduces the IP multimedia subsys-
tem for efficiently providing IP based multime-
dia services over the packet domain. The IP
Multimedia subsystem is an overlay control sys-
tem to perform session control of IP multimedia
services based on SIP signalling. The transport
part is evolving towards an “All IP” architecture,
e.g. the transport for the CS domain could be
transported by IP through the CN.

In the following we provide a short description
of the core network, the radio network and the

IP multimedia subsystem. Our focus will be on

the PD of UMTS.

2.1 Core Network

The Core Network [5,6,7] transports packets

between the radio access network and external

IP networks. Besides this transport function it

is also responsible for Lawful Intercept, Charg-

ing, authenticating users and authorising connec-

tions to the external IP networks as well as func-

tionality specific to mobile networks such as

mobility management. The three main nodes of

the Core Network are the Home Subscriber

Server (HSS), the Serving GPRS support node

(SGSN) and the Gateway GPRS Support Node

(GGSN).

The Home Subscriber Server (HSS) is the mas-

ter database for a given user. It is the entity con-

taining the subscription related information to

support the network entities actually handling

calls/sessions. The HSS includes the GSM HLR

functionality and IETF AAA functionality.

The SGSN is the node that serves the MS. The

SGSN supports GPRS for GSM and/or UMTS.

When the mobile is attaching to the network, the

SGSN establishes a mobility management con-

text that records the mobility and security infor-

mation of the mobile. When the mobile wants to

establish a connection to external networks it

initiates PDP Context Activation procedure. The

SGSN participates in that procedure and keeps

track of the parameters (Routing information,

QoS information) of that connection in a PDP

context.

Figure 2-1 UMTS

Architecture

HSS IP Multimedia Subsystem

R-SGW

UMTS Service Platform

(OSA, CAMELJAIN/PARLAY..)

U

T

R

A

N

2 G Signalling

Network =

(IS-136,++?) GSM

IP

(Internet, Intranet)

Networks

PSTN / ISDN / GSM

PS Domain

CS Domain

UMTS Core Network

SGSN GGSN

MGW

CS-MGW CS-MGW

MSC-server IP GMSC-server T-SGW

IP

IP

IP

IP IP

IP

IP

IP