Integration Of UMTS And B-ISDN: Is It Possible Or Desirable?

INTRODUCTION

In the future, existing fixed networks will be complemented by mobile networks
with similar numbers of users. These mobile users will have identical
requirements and expectations to the fixed users, for on-demand applications of
telecommunications requiring high bit-rate channels. It will be necessary for
these fixed and mobile networks to interoperate in order to pass data, in real
time and at high speeds, between their users.

But how far must this interoperation be taken? How much integration of the fixed
and mobile network structures is needed? Here, a fixed network, B-ISDN, and a
mobile network, UMTS, under development at the same time, are examined to see
how well and closely they should work together in order to meet expected user
needs. Work already taking place on this is discussed.

BACKGROUND

The Universal Mobile Telecommunication System (UMTS), the third generation of
mobile networks, is presently being specified as part of the European RACE
technology initiative. The aim of UMTS is to implement terminal mobility and
personal mobility within its systems, providing a single world mobile standard.
Outside Europe, UMTS is now known as International Mobile Telecommunications
2000 (IMT2000), which replaces its previous name of Future Public Land Mobile
Telecommunication System (FPLMTS). [BUIT95]

UMTS is envisaged as providing the infrastructure needed to support a wide range
of multimedia digital services, or teleservices [CHEU94], requiring channel bit-
rates of less than the UMTS upper ceiling of 2 Mbits/second, as allocated to it
in the World Administrative Radio Conference (WARC) \'92 bands. UMTS must also
support the traditional mobile services presently offered by separate networks,
including cordless, cellular, paging, wireless local loop, and satellite
services. [BUIT95] Mobile teleservices requiring higher bit rates, from 2 to 155
Mbits/second, are expected to be catered for by Mobile Broadband Services (MBS),
the eventual successor to UMTS, which is still under study. [RACED732]

Broadband Integrated Services Digital Network (B-ISDN), conceived as an all-
purpose digital network that will supersede Narrowband ISDN (N-ISDN or ISDN), is
also still being specified. B-ISDN, with its transport layer of Asynchronous
Transfer Mode (ATM) is expected to be the backbone of future fixed digital
networks. [MINZ89]

It is anticipated that, by the year 2005, up to 50% of all communication
terminals will be mobile. [CHEU94] The Mobile Green Paper, issued by the
European Commission in 1994, predicts 40 million mobile users in the European
Union by 2000, rising to 80 million by 2010. This gives mobile users an
importance ranking alongside fixed-network users. [BUIT95]

One result of this growth in mobile telecommunications will be the increase in
teleservice operations that originate in either the fixed or mobile network, but
terminate in the other, crossing the boundary between the two. UMTS is expected
to be introduced within the next ten years, and integration with narrowband and
broadband ISDN is possible in this time. Interoperability between UMTS and ISDN
in some fashion will be necessary to support the interoperability between the
fixed and mobile networks that users have already come to expect with existing
mobile networks, and to meet the expectation of consistency of fixed/mobile
service provision laid out in the initial RACE vision. [SWAI94]

One way of making UMTS attractive to potential customers is to offer the same
range of services that B-ISDN will offer, within the bounds of the lower 2
Mbits/second ceiling of UMTS. [BUIT95]

So, with the twin goals of meeting existing expectations and making UMTS as
flexible as possible to attract customers, how closely integrated must UMTS be
with B-ISDN to achieve this?

ALTERNATIVES FOR INTEGRATING UMTS WITH OTHER NETWORKS

The UMTS network could be developed along one of the following alternative
integration paths:

1. Developing an \'optimised\' network structure and signalling
protocols tailored for the special mobile requirements of
UMTS. This would be incompatible with anything else. Services
from all fixed networks would be passed through via gateways.
This design-from-scratch method would result in highly
efficient intra-network operation, at the expense of highly
inefficient inter-network operation, high development cost,
scepticism relating to non-standard technology, and slow
market take-up. True integration with fixed networks is not
possible in this scenario.

Given the drawbacks, this is not a realistic option, and it
has not been considered in depth. One of the RACE goals was to
design UMTS not as a separate overlay network, but to allow
integration with a fixed network; this option is undesirable.
[BUIT95]

2. Integration with and evolution from the existing Global
System for Mobile telecommunication. (GSM, formerly standing
for Group Special Mobil during early French-led specification,
is now taken as meaning Global System for Mobile
communications by the