Side_1_360

The main entity is the Call State Control Func-
tion (CSCF). The CSCF is responsible for the
call control part of the IP multimedia services.
It is very similar to a SIP server deploying the
Session Initiation Protocol (SIP).

To support the IP multimedia traffic SIP is cho-
sen to carry the call control signalling peer-to-
peer. This protocol family is looked upon as the
most promising multimedia protocol as the trend
has turned toward a major growth in IP based
applications and multimedia. SIP is an applica-
tion-layer control protocol that can establish,
modify and terminate multimedia sessions. Con-
ceptually it inherits features from other IETF
protocols, in particular Simple Mail Transfer
Protocol (SMTP) and Hyper Text Transfer Pro-
tocol (HTTP). The SIP is a textual protocol
based on a client-server model. Both the client
and server parts of SIP are however imple-
mented in a user terminal.

The Multimedia Resource Function (MRF) per-
forms multiparty call and multimedia conferenc-
ing functions. MRF would have similar func-
tions as an MCU in an H.323 network.

It is also responsible for bearer control (with
GGSN) in case of multiparty/multimedia confer-
ences. It may also communicate with the CSCF
for service validation for multiparty/multimedia
sessions. Other entities are used to provide inter-
working with legacy circuit switched networks
(GSM/PSTN/ISDN).

The next chapter presents the QoS framework
of UMTS [1,2]. The development of this frame-
work has been done incrementally. In the first
release of UMTS only internal UMTS QoS is
provided, i.e. QoS from the mobile termination
to the Gateway (GGSN). The next releases
develop the framework further by including end-
to-end QoS support.

3 UMTS QoS Architecture

3.1 UMTS QoS development

The UMTS QoS framework is being established
based on a set of requirements of both general
and technical character. The requirements incor-
porate internal as well as the end-to-end aspects.
Some of these requirements are given in Figure
3-1.

During the work these QoS requirements act as
strict working rules for the QoS team in 3GPP.
However, before starting the QoS specification,
a system perspective had to be clarified in terms
of which bearer services the UMTS system con-
tained, and how they interacted. The bearers
comprise a framework of how the QoS func-
tional entities interact. It also showed how the

bearers supported each other regarding what

information had to be conveyed both vertically

and horizontally to establish a QoS path across

the UMTS network as well as end-to-end.

To ensure QoS across the UMTS network, vari-

ous attributes, e.g. error tolerance, delay values,

SDU sizes, were described as guidelines for the

real implementation. It was crucial that the

UMTS system was seen as a network with inter-

nal budgets on e.g. delay and jitter and that the

end-to-end QoS requirements between two com-

municating subscribers would be met. Delay

budgets for the different network segments were

derived from several studies on customer satis-

faction as well as the feasibility of the network

components and transmission links. To differen-

tiate between different traffic requirements, spe-

cific UMTS QoS classes were described. These

classes should ensure that the characteristics and

requirements of each individual traffic flow

would be met.

The UMTS system should interact with legacy

networks. This interoperability between different

wireless systems was felt necessary given that

many operators have large investments in 2G

systems. QoS parameters therefore have to be

mapped between the different systems, and map-

Figure 3-1 Technical

requirements regarding

QoS for UMTS

Requirements for UMTS QoS

• UMTS shall provide QoS attribute control on a peer-to-peer basis between UE
  and 3G gateway node;


• UMS QoS shall provide a mapping between applications requirements and
  UMTS services;


• UMTS QoS shall be able to efficiently interwork with current QoS schemes.
  Further, the QoS concept should be capable of providing different levels of
  QoS by using UMTS specific control mechanisms (not related to QoS mecha-
  nisms in the external networks);


• A session based approach needs to be adopted for all packet mode commu-
  nication within the 3G serving node with which UMTS QoS approach shall be
  intimately linked, essential features are multiple QoS streams per address;


• The overhead and additional complexity caused by the QoS scheme should
  be kept reasonably low, as well as the amount of state information transmitted
  and stored in the network;


• QoS shall support efficient resource utilisation;


• The QoS attributes are needed to support asymmetric bearers;


• Applications (or special software in UE or 3G gateway node) should be able
  to indicate QoS values for their data transmissions;


• QoS behaviour should be dynamic, i.e. it shall be possible to modify QoS
  attributes during an active session;


• Number of attributes should be kept reasonably low (increasing number of
  attributes, increased system complexity);


• User QoS requirements shall be satisfied by the system, including when
  change of SGSN within the Core Network occurs.