ATM-over-satellite demonstration of broadband network interconnection
Introduction
Demand for cost-effective interconnection of private and public broadband islands such as ATM local area networks (LANs), DQDB MANs and local experimental ATM networks 1, 2is increasing. However, there is a shortage of broadband terrestrial connections in wide areas, particularly in more remote or rural areas where terrestrial lines are expensive to install and operate. Satellites can be used to complement terrestrial networks by extending the broadband networks with its flexibility and immediate wide coverage. The RACE II CATALYST project was a three-year European project that developed an experimental broadband satellite system based on ATM links. The objective of the broadband satellite system was to provide interconnection to geographically dispersed broadband networks called `broadband islands', and to further stimulate the introduction of broadband application services across Europe. The first CATALYST demonstration took place in December 1992 and involved the first transmission of ATM cells over satellite in Europe.
The satellite system was based on ATM transport permitting direct compatibility with the future ATM-based B-ISDN. It is now widely accepted that the ATM-based B-ISDN will not be a revolution but an evolution which will take several years. Considering this, the CATALYST satellite bridge has been designed to be able to interconnect the ATM networks as well as existing networks such as the LANs and MANs. Fig. 1 illustrates an example of configuration of the satellite demonstrator. A modular approach has been used in the design to interface different networks and the satellite, converting network packets to and from ATM cells.
The satellite ATM equipment has to interface the networks with the capacities in the range of 10 to 150 Mbit/s (10 Mbit/s for Ethernet, 34 Mbit/s for DQDB, 100 Mbit/s for FDDI and 150 Mbit/s for ATM networks). The satellite has a link capacity of approximately 25 Mbit/s per transponder at present and will perhaps never be able to match the speed of optical fibre terrestrial networks. The satellite link capacity has to be shared by a number of earth stations when multiple broadband islands are interconnected. It is important to study the model of the satellite demonstrator to provide the required quality of service (QoS) with efficient utilisation of the satellite resources.
Owing to the nature of satellite links, the effects caused by long propagation delay become a very important issue. For example, voice and video applications are more sensitive to the long delay than data applications. Delay variations can significantly degrade the QoS. The delay also affects throughput of the connections based on different protocols, such as connection-oriented and connectionless protocols. The connection-oriented protocols requiring acknowledgements of packet arrival may need to increase the time-out parameter or window size to accommodate the long propagation delay (see Ref. [3]for TCP extensions). Hence, adjustment of existing protocols or development of new ones are required to support the B-ISDN applications efficiently.
This paper tries to study these issues, including the effects on the applications and protocols. First the architecture and modelling of the ATM satellite equipment are described. Then the demonstrated applications and measurements which were carried out are explained. This is followed by a discussion of the effect of long propagation delay on the protocols and applications based on the model. Furthermore, resource management for the satellite system and its impact on the system design and performance are described. Then traffic and congestion control methods to improve the performance of the system are explained, followed by progress on ATM over satellite research in Europe since CATALYST within research and development in advanced communications technologies in Europe (RACE) and advanced communications technologies and services (ACTS). Finally, the importance of access schemes which can provide dynamic bandwidth allocation and the reasons in the evolution of satellite ATM systems from traditional `bent-pipe' satellites to on-board processing satellites with spot beams and cell switching capabilities are explained.
Section snippets
The ground segment
Most of the development in this project was on the ground segment. A modular approach was used in the design, where each module had a buffer(s) for packet/cell conversion and/or traffic multiplexing. Fig. 2 illustrates the model of the ground equipment. The following is a brief description of these modules.
Demonstrated services and applications
Demonstration was a significant step to show how the broadband services could be affected by the ATM satellite systems. A number of applications had been demonstrated based on the CATALYST demonstrator that included the following.
Interactive image: this is a client–server application, where about 200 images are available in the server database with size range from 4 to 8 Mbit/s per image. The client terminals can access these images, modify them by means of a light pen, and transfer the results
Resource management (RM) for the satellite ATM system and its impacts
There are three levels of RM mechanisms in the satellite system. The first level is controlled by the network control centre (NCC) to allocate the bandwidth capacity to each earth station. The allocation is in the form of burst time plans (BTPs). Within each BTP, burst times are specified for the earth station that limit the number of cells in bursts the earth stations can transmit. In the CATALYST demonstrator, the limit is that each BTP is less than or equal to 960 ATM cell and the sum of the
Traffic and congestion control
The CATALYST system can cope efficiently with traffic flowing from the network with bit rates up to 20.352 Mbit/s (excluding the overhead of the ATM cells) and even higher bit rates in a shorter burst if traffic control mechanisms are used. The CATALYST demonstrator did not use any traffic control functions apart from RM, which can be used to allocate network resources to separate traffic according to service characteristics. Thus, this section will describe methods by which the system
Progress since the CATALYST
Since the implementation of the first demonstrator in December 1992, which realised the first European ATM link via satellite, RACE projects and some EC ACTS projects have been demonstrating and investigating ATM-over-satellite applications and performance. The CATALYST project was indeed a catalyst in getting the integrated broadband communication (IBC) started. This section will describe other RACE and ACTS projects on ATM over satellite which have been started after the success of the
Evolution of ATM satellite systems
Whilst fibre optics are rapidly becoming the preferred carrier for high bandwidth communication services, satellite systems can play an important role in the B-ISDN. The satellite network configuration and capacity can be increased gradually to match the increasing B-ISDN traffic during the evolution toward broadband communications.
The role of satellites in high-speed networking will evolve according to the evolution of the terrestrial ATM-based B-ISDN. However, two main roles can be identified
Conclusions
This paper presented the architecture of the demonstrator developed by the CATALYST project and the studies of ATM over satellite for broadband communications. The ground segment, multiple-access scheme, space segment and protocol stack were described.
The study and demonstrated services and applications showed the capability of ATM over satellite to support data, voice, video and multimedia communications over GEO satellites. Although only limited measurements were taken from the demonstrators,
Acknowledgements
The authors gratefully acknowledge the support from the CEC RACE programme, the RACE II CATALYST project (R2074) and the Engineering and Physical Science Research Council (EPSRC).
Dr. Zhili Sun received his B.Sc. from Nanjing University, China and his M.Phil. and Ph.D. from Lancaster University, UK. He is currently a Senior Research Fellow and the head of the Network Research Group in the Centre for Communication Systems Research, University of Surrey, UK.
He was a Postdoctoral Researcher, from 1989 to 1993, in the Telecommunication Group, Queen Mary and Westfield College, University of London, worked on the RACE I R1022 project `Technology for ATD' to develop
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Dr. Zhili Sun received his B.Sc. from Nanjing University, China and his M.Phil. and Ph.D. from Lancaster University, UK. He is currently a Senior Research Fellow and the head of the Network Research Group in the Centre for Communication Systems Research, University of Surrey, UK.
He was a Postdoctoral Researcher, from 1989 to 1993, in the Telecommunication Group, Queen Mary and Westfield College, University of London, worked on the RACE I R1022 project `Technology for ATD' to develop specification, system design and test systems based on ATM technology, and on the RACE II R2061 `Exploit project' to implement an ATM testbed and studying traffic engineering and performance of the testbed.
He worked as one of the key members, from 1993 to 1995, in the RACE programme II R2074 `CATALYST project' which developed a satellite ATM demonstrator to study the capability of satellite for supporting B-ISDN. He also worked in an EPSRC project `B-ISDN implementation via satellite—ATM island interconnection'.
He is also a co-ordinator of the THESEUS project, within the European Advanced Communications and Technologies (ACTS) programme and workpackage, leading workpackage 4 (network aspects) and 7 (field trials) of the project, teaches M.Sc. and industrial short courses on ATM and broadband networks and communications.
Tolga Örs received the B.Sc. degree in Electronic Engineering from the Electronic Engineering Dept., Istanbul University, Turkey, and the M.Sc. with Distinction in Satellite and Telecommunication Engineering from the Electronic and Electrical Engineering Dept., University of Surrey, UK.
He is currently a Ph.D. student in the Centre for Communication Systems Research (CCSR), University of Surrey, working on optimisation and performance evaluation of ATM traffic control functions for terrestrial and satellite networks. He is contributing to ATM traffic characterisation and modelling for the GIPSE (Global Integrated Personal Satellite multimedia Environment) project.
His research interests include traffic management in ATM networks, ATM internetworking, real-time scheduling in high speed networks and traffic modelling.
Professor Barry Evans received the B.Sc. and Ph.D. in Electrical Engineering and Microwave Systems from the University of Leeds in 1965/1968. He was British Telecom Lecturer–Reader in Telecommunications Systems at the University of Essex from 1969–1983. In 1983 he was appointed to the Alec Harley Reeves Chair of Information Systems Engineering at the University of Surrey, and in 1990 became the first Director of the post-graduate centre for Satellite Engineering Research which houses some 100 researchers.
He serves on several IEE professional groups and CCIR study groups and for 8 years has run the IEE Vacation School on Satellite Communications at Surrey. In 1990 he was elected to a Fellowship of the Royal Society of Arts and Manufacturing Sciences and in 1991 a Fellow of the Royal Academy of Engineering.
Barry Evans is editor of the International Journal of Satellite Communications and author of three books and over 200 journal papers.