Integration Of UMTS And B-ISDN: Is It Possible Or Desirable? Essay, Research Paper
Integration Of UMTS And B-ISDN: Is It Possible Or Desirable?
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.
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
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
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.
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 non-French-speaking world.) GSM is
currently being introduced on the European market.
This option has the advantage of using already-existing mobile
infrastructure with a ready and captive market, but at the
expense of limiting channel bit-rate considerably, which in
turn limits the services that can be made available over UMTS.
Some of the technical assumptions of UMTS, such as advanced
security algorithms and distributed databases, would require
new protocols to implement over GSM. GSM would be limiting the
capabilities of UMTS. [BROE93a]
3. Integration with N-ISDN. Like the GSM option above, this
initially limits UMTS’s channel bit-rate for services, but has
a distinct advantage over integration with B-ISDN – N-ISDN is
widely available, right now. However, integrating UMTS and
N-ISDN would require effective use of the intelligent network
concept for the implementation of mobile functions, and
modification to existing fixed network protocols to support
Integrating UMTS with N-ISDN makes possible widespread early
introduction and interoperability of UMTS in areas that do not
yet have B-ISDN available. This allows wider market
penetration, as investment in new B-ISDN equipment is not
required, and removes the dependency of UMTS on successful
uptake of B-ISDN for interoperability with fixed networks.
Eventual interoperability with B-ISDN, albeit with
constrictions imposed on UMTS by the initial N-ISDN
compatibility, is not prevented. [BROE93a]
4. Integration with B-ISDN. This scenario was the target of
MONET (MObile NETwork), or RACE Project R2066. Unlike the
above options, B-ISDN’s high available bandwidth and feature
set does not impose limitations on the service provisioning in
UMTS. Fewer restrictions are placed on the possible uses and
marketability of UMTS as a result. Development of B-ISDN is
taking place at the same time as UMTS, making smooth
integration and adaptation of the standards to each other
For these reasons, integration of UMTS with B-ISDN has been accepted as the
eventual goal for interoperability of future fixed and mobile networks using
these standards, and this integration has been discussed in depth. [BROE93a,
BROE93b, BUIT95, NORP94]
At present, existing B-ISDN standards cannot support the mobile-specific
functions required by a mobile system like UMTS. Enhancements supporting mobile
functions, such as call handover between cells, are needed before B-ISDN can act
as the core network of UMTS.
Flexible support of fixed, multi-party calls, to allow B-ISDN to be used in
conferencing and broadcasting applications, has many of the same requirements as
support for mobile switching, so providing common solutions to allow both could
minimise the number of mobile-specific extensions that B-ISDN needs.
As an example of how B-ISDN can be adjusted to meet UMTS’s needs, let’s look at
that mobile requirement for support for call handover. Within RACE a multiparty-
capable enhancement of B-ISDN, upwardly compatible with Q.2931, has already been
developed, and implementing UMTS with this has been studied. For example, a UMTS
handover can be handled as a multi-party call, where the cell the mobile is
moving to is added to the call as a new party, and the old cell is dropped as a
party leaving the call, using ADD(_party) and DROP (_party) primitives. Other
mobile functions can be handled by similar adaptations to the B-ISDN protocols.
The enhancements to B-ISDN Release 2 and 3 that are required for UMTS support
are minimal enough to be able to form an integral part of future B-ISDN
standards, without impacting on existing B-ISDN work. [BUIT95]
These modifications only concern high-level B-ISDN signalling protocols, and do
not alter the transport mechanisms. The underlying ATM layers, including the ATM
adaptation layer (AAL) are unaffected by this.
THE INTELLIGENT NETWORK
The Intelligent Network (IN) is a means for service providers to create new
services and rapidly introduce them on existing networks. As the IN was
considered useful for implementing mobility procedures in UMTS, it was studied
as part of MONET, and is now specified in the Q.1200 series of the ITU-T
The intelligent network separates service control and service data from basic
call control. Service control is then activated by ‘trigger points’ in the basic
call. This means that services can be developed on computers independent of the
network switches responsible for basic call and connection control. This gives
flexibility to the network operators and service providers, as well as the
potential to support the services on any network that supports the trigger
points. Eventually, IN can be expanded to control the network itself, such as
handling all UMTS mobile functions. [BROE93a]
Any network supporting the intelligent network service set will be able to
support new services using that service set easily, making integration of
networks easier and transparent to the user of those services. The intelligent
network is thus an important factor in the integration of B-ISDN and UMTS. UMTS,
B-ISDN and the intelligent network set are all being developed at the same time,
allowing each to influence the others in producing a coherent, integrated whole.
In order to be accepted by users as useful and to provide as wide a variety of
services as possible, UMTS needs some form of interoperabilty or integration
with a fixed network. Integration of UMTS with B-ISDN offers the most
flexibility in providing services when compared to other network integration
options, and constrains UMTS the least.
With the increase in the number of services that will be made available in UMTS
and B-ISDN over present standalone services, it is unrealistic to develop two
separate, and incompatible, versions of each service for the fixed and mobile
networks. Integrating UMTS and B-ISDN makes the same service set available to
both sets of users in the same timescale, reducing development costs for the
services, and promoting uptake and use in the market. The intelligent network
concept allows the easy provision of additional services with little extra
development cost. Integrating UMTS with B-ISDN, and with the intelligent network
set, is therefore desirable.
Work on this integration indicates that the mobile requirements of UMTS can be
met by extending existing B-ISDN signalling to handle them, without
significantly modifying B-ISDN. Integration of UMTS with B-ISDN is therefore
[BROE93a] W. van den Broek, A. N. Brydon, J. M. Cullen, S. Kukkonen, A. Lensink,
P. C. Mason, A. Tuoriniemi, “RACE 2066: Functional models of UMTS and
integration into future networks”, IEE Electronics and Communication Engineering
Journal, June 1993.
[BROE93b] W. van den Broek and A. Lensink, “A UMTS architecture based on IN and
B-ISDN developments”, Proceedings of the Mobile and Personal Communications
Conference, 13-15 December 1993. IEE Conference Publication 387.
[BUIT95] E. Buitenwerf, G. Colombo, H. Mitts, P. Wright, “UMTS: Fixed network
issues and design options”, IEEE Personal Communications, February 1995.
[CHEU94] J. C. S. Cheung, M. A. Beach and J. P. McGeehan, “Network planning for
third-generation mobile radio systems”, IEEE Communications Magazine, November
[MINZ89] S. E. Minzer, “Broadband ISDN and Asynchronous Transfer Mode (ATM)”,
IEE Communications Magazine, September 1989.
[NORP94] T. Norp and A. J. M. Roovers, “UMTS integrated with B-ISDN”, IEEE
Communications Magazine, November 1994.
[RACED732] IBC Common Functional Specification, Issue D. Race D732: Service
[SWAI94] R. S. Swain, “UMTS – a 21st century system: a RACE mobile project line