Tolga Örs

A meshed VSAT satellite network architecture using an on-board ATM switch

This paper proposes a meshed very small aperture terminal (VSAT) satellite communications network which uses an on-board processing (OBP) satellite with spot beams and cell switching capabilities. A novel approach is used for maximizing the bandwidth utilization of the satellite by performing statistical multiplexing on-board the satellite. MF-TDMA is used as the satellite multiple access protocol since it takes advantage of the flexibility and statistical multiplexing capabilities of ATM. Finally, the cell loss resulting from the limited bandwidth of the satellite link can be prevented by effective traffic control functions. A preventive control scheme has been used for this purpose. The leaky bucket (or generic cell rate algorithm) used as usage parameter control (UPC) controls the source traffic parameters for conformance with the traffic contract. Furthermore a rate-based flow control is used to control ABR services. The results of the performance analysis of the proposed system indicate that a high increase in satellite bandwidth utilization can be achieved, compared to circuit-switched satellite systems.

ATM-over-satellite demonstration of broadband network interconnection

This paper presents the architecture and performance studies of demonstrations of broadband network interconnection using ATM over satellite developed in the RACE II CATALYST project. The purpose of the project was to develop an ATM satellite link for future B-ISDN services, particularly for the interconnections of ATM testbeds which are in the form of broadband islands. By interconnecting these broadband islands, the initial ATM-based B-ISDN can be introduced, thus getting the integrated broadband communication started. The CATALYST project has developed the satellite ATM demonstrator to be able to interconnect newly developed ATM testbeds as well as the existing networks such as DQDB, FDDI and Ethernet. Experiments demonstrated the capability of the satellite ATM connections to support data, voice, video and multimedia applications. These experiments provided a real system demonstration of ATM over satellite. In the light of the experiment, this paper studies the relevant issues and the impact of ATM over satellite on the applications and the protocols. Furthermore, techniques to improve the performance of the system, such as congestion control and dynamic bandwidth allocation, are explained and information on progress is provided.

Analysis of an adaptive random/reservation MAC protocol for ATM over satellite

We analyse the performance of an adaptive random-reservation medium access control (MAC) protocol which can support all ATM service classes while providing the required quality of service (QoS). Our study focuses on parameter optimisation of the multiple access schemes for ATM over a GEO satellite with on-board processing capabilities, considering various traffic mixes of constant bit rate (CBR), real-time VBR (RT-VBR), non-real time VBR (NRT-VBR) and unspecified bit rate (UBR). It is shown that maximum throughput can be achieved by using this access scheme. A TDMA access protocol combining both random access and demand assignment multiple access (DAMA) is particularly suited for a scenario with a high number of terminals with very bursty UBR traffic (e.g. Web browsing). UBR sources with short burst length access the slots remaining after the reservation procedure by random access which drastically reduces the slot access delay, at the expense of lower utilisation. However for UBR sources with burst sizes consisting of several ATM cells, reservation access provides higher throughput but the access delay is considerable longer.

A study of TCP/IP throughout performance in heterogeneous ATM local area networks

This paper investigates the maximum throughput performance of TCP/IP over ATM-based local area networks. The testbeds for the measurements use second- generation ATM switches to interconnect various personal computers and workstations in a heterogeneous environment. The effects of parameters such as socket buffer size and message size on TCP/IP performance over ATM adaptation layer 5 are studied. The results are compared with the calculated theoretically available maximum bandwidth offered by ATM, and an estimation of the limits caused by the processing power of the computers involved. Explanations for the observed behaviour are given.

Analysis of a MAC protocol to guarantee QoS for ATM over satellite

In this paper we analyse the performance of a medium access control (MAC) protocol which is particularly suited for a scenario with a high number of terminals with very bursty unspecified bit rate (UBR) traffic (e.g. web browsing). In order to guarantee the required quality of service (QoS) requested by the user for all ATM service classes, priorities between the service classes must be implemented. Hence prioritised queueing of requests is proposed. The adaptive MAC protocol was designed to allow statistical multiplexing of ATM traffic over the air interface, especially for independent and spatially distributed terminals. It is shown that the potential user population which can be served is considerably increased by statistically multiplexing bursty traffic over the air interface.

An adaptive random-reservation MAC protocol to guarantee QoS for ATM over satellite

In this paper we analyse the performance of an Adaptive Random-Reservation Medium Access Control (MAC) protocol which can support all ATM service classes while providing the required Quality of Service (QoS). Our study focuses on parameter optimisation of the multiple access schemes for ATM over a GEO satellite with on-board processing capabilities, considering various traffic mixes of Constant Bit Rate (CBR), real-time Variable Bit Rate (rt VBR), non-real-time VBR (nrt VBR) and Unspecified Bit Rate (UBR). It is shown that maximum throughput can be achieved by using this access scheme. A TDMA access protocol combining both Random Access and Demand Assignment Multiple Access (DAMA) is particularly suited for a scenario with a high number of terminals and very bursty UBR traffic (e.g. web browsing). UBR sources with short burst length access the slots remaining after the reservation procedure by random access which drastically reduces the slot access delay, at the expense of lower utilisation.

ATM over VSAT networks using traditional bent-pipe or on-board processing satellites

In this paper two VSAT satellite network architectures are proposed to offer access to the B-ISDN and accommodate ATM service needs in an integrated manner, while achieving maximum bandwidth utilisation of the satellite. The first architecture uses a traditional ‘bent pipe’ repeater satellite. The need for optimization of the channel capacity allocation scheme is discussed, using a preliminary performance analysis for a Dynamic Reservation TDMA system which takes advantage of the flexibility and the statistical multiplexing capabilities of ATM and supports various VBR and CBR services. Some bottlenecks, introduced by the satellite link, in the performance of protocols such as TCP/IP are highlighted. The second architecture uses an OBP satellite with spot beams and cell-switching capabilities. A novel approach, in which statistical multiplexing is performed on-board the satellite, is suggested and results show that a much better satellite bandwidth utilization can be achieved. In this architecture, smaller earth terminals can be used without complex dynamic reservation protocols, but at the cost of a more complex satellite payload.