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ACTSLINE Guideline Summary NIF-G4

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A Generic Interface BetweenAccess And Core Networks

An area of particular interest is the increasing integration and interworking of networks. As we move

from the existing discrete networks to networks with a high potential for interconnection, it is important

to have well defined, flexible interfaces. A particularly important example of this is the interface

between future access networks and the core networks.

A number of ACTS projects have studied the interface between mobile access networks and core

networks. This interface is generally referred to as the Iu (Interface UMTS1) or Generic Interface.

The Iu interface is primarily an interface between radio (or satellite) access networks and core

networks. The experiences of these projects have been brought together in a Guideline entitled

Requirements On The Iu Interface Between Access And Core Networks .

In Europe, the Iu interface is intended to interconnect all possible access networks (both present and

foreseen in the near future) to all possible core networks (again both present and foreseen in the near

future). It therefore provides a smooth evolution path from GSM and from the fixed network towards aUMTS convergent solution.

The basic requirements of the interface

When considering network integration in the long term, it is important that any solution allows not just

interworking between different networks, but stable integration. In this sense, the guideline describes a

long term scenario. It highlights the requirements that the various networks put on the Iu interface, both

from the access and the core side. The way the Iu interface is defined strongly supports the re-use of

existing resources, components, protocols and services as far as possible.

The requirements for the Iu interface can be described in terms of the functions that need to send

messages through this interface. They are:

Bearer Control Call Control Mobility Management Handover and Macrodiversity Radio Resources Management Security

The recommendations given in the guideline (and summarised below) support these functions.

Reference Configuration

When describing any interface between networks, it is helpful to have a network configuration to use asa reference. Figure 1 shows such a configuration. In this, the Iu interface (or the Generic Interface)

connects the access sector to the core one. In both sectors, existing networks continue to exist with

UMTS networks.

1 UMTS is the Universal Mobile Telephone System.


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Generic

Core

Networks

(GSM/UMTS, N/B-ISDN/UMTS, ...)

UMTS GRAN

Radio Independent Part

Generic (Iu) Interface

NB-ISDN INTERNET

GSM Network

Adaptation

N/B-ISDN Nt.

Adaptation

INTERNET Nt.

Adaptation

UMTS GRAN

Radio AccessPart #1

UMTS GRAN

Radio AccessPart #n

UMTS GRANRadio Dependent

Part #1

UMTS GRANRadio Dependent

Part #n

UMTS GRANGSM Radio

Dependent Part

UMTS GRANDECT Radio

Dependent Part

UMTS GRANSAT Radio

Dependent Part

GSM RadioAccess Part

DECT RadioAccess Part

SAT RadioAccess Part

GSM

CORE NETWORK

Fig. 1 - Reference Configuration for GENERIC ACCESS AND CORE NETWORKS

This figure is useful for two main reasons:

It illustrates the role of the Iu interface based on UMTS. Although adaptation functions arenecessary between existing core networks and the Iu interface, no adaptation function is needed

between the UMTS core network and the Iu interface.

It illustrates the characteristics of the Iu interface as a generic interface. By separating the radiodependent and independent parts in the access network, the difference between several radio access

techniques (e.g. CDMA, TDMA) can be solved at the access network level. This allows the Iuinterface to be generic.

Recommendations for the Iu interface

The first five recommendations in the guideline have general characteristics, while the others refer to

specific functions.

General

The Iu interface should support routing and addressing of signalling messages

A UMTS network can contain a number of different entities, which need to receive and send control (orsignalling) messages. The Iu interface needs to support the routing of these signalling messages to their

destinations.

The Iu interface should support free allocation of functionality

There will be no single, unique structure of a UMTS network. UMTS environments will differ in the

number of entities they contain, as well as in the way these entities are interconnected. As a

consequence, the way that the functions of the access network are distributed between these entities will

vary. The Iu interface will have to support this flexibility.

The Iu interface should support implicit addressing

Mobile terminals should only be allowed to identify the type of functions they need to use in the

network, rather than explicitly identifying a specific element of the network in which that function is

implemented.


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The Iu interface should support generic function messages, while system specific messages should

be terminated in the particular system

Where several systems are co-existing and interconnected, there is a need for a common basis for

communication between the systems. A good example of this is the Call Control functionality.

Generic Call Control messages (e.g. call set-up etc.) which are used in all types of systems, must besupported by the Iu interface. The information contained within these messages has to be mapped onto a

generic set of identifiers and elements. Messages that are specific to a certain system (e.g. the DECT-

CC-INFO message) have to be terminated within that system, rather than be passed to systems which do

not understand them and have no use for them.

The Iu interface should be aligned with GSM A interface

GSM is currently a very widespread system. UMTS is intended to have backward compatibility

towards all the present systems, and must therefore take particular account of GSM characteristics.

Bearer & Call Control

The Iu interface should perform UMTS Bearer Control by re-using fixed Call Control functions

This is a typical opportunity for re-use. In Bearer Control, what is needed is point-to-point connection

capability. This is already offered, for example, by B-ISDN Call Control. The only modification

needed is the introduction of suitable mobility parameters.

The Iu interface should support separation between call and bearer control

In a mobile call, connections can change during the same call (handover). In this case, the bearer

control may change, but there is no need to change the call control. Another reason for such separation

may reside in Radio Resource Management, e.g. for enhanced bearer capability. In this case many

bearers could serve a single call, thus reinforcing the need for separate bearer and call control.

Mobility Management

The Iu interface should not only support user registration and location update but also domain

update for changing networks

In UMTS it will be possible to not only to change location in the same domain but also to change

operator or network (e.g. GSM - UMTS). The Iu interface will have to support this change.

Handover and Macrodiversity

The Iu interface should support Handover and Macrodiversity between entities at the level of core

network access point

When the terminal is crossing the boundary of a transceiver controller (e.g. CSS in UMTS), handover

should be performed at Local Exchange level, unless the transceiver controllers are not connected to

each other.

Radio Resources Management

The Iu interface should be as free as possible of influences regarding the Radio Resources

Management

All of the Radio Resources Management issues (power control algorithms, timing issues, radio channel

management, medium access control) should be performed as far as possible in the Access Network and

therefore should not need to cross the Iu interface..


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Security

The Iu interface should support multiple authentication mechanisms

UMTS has a primary goal of flexibility and global interworking/integration. This will only be possible

if robust security mechanisms are supported by the interface. To achieve this, mutual authentication

between all pairs of entities interacting across the interface (eg user, network operator and serviceprovider) is needed.

Unsolved Problems

Both the UMTS network architecture and the Iu interface framework are still in development. Because

of that, it may not be clear how any single function will be implemented, namely whether across or only

at one side of the Iu interface. An example could be that of Radio Resources Management, which could

be implemented entirely in the Access Network.

Conclusions

The increasing emphasis on mobility and network integration, means that the definition of a genericinterface between access networks and core networks is vital. The Iu interface meets this need and the

guideline lays down some of the basic features needed of this interface.

More details of the ACTS guidelines can be found at

http://www.infowin.org/ACTS/ANALYSYS/CONCERTATION/glindex.htm

Wes CarterACTSLINE

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