Performance of Multicast File Transfer Protocol (MFTP) over Geostationary Satellite Systems with DAMA Uplinks

Abstract

Their inherent broadcasting capabilities over very large geographical areas make satellite systems one of the most effective vehicles for multicast service delivery. Recent advances in spotbeam antennas and high-power platforms further accentuate the suitability of satellite systems as multicasting tools. The focus of this article is reliable multicast service delivery via geostationary satellite systems. Starburst MFTP is a feedback-based multicast transport protocol that is distinct from other such protocols in that it defers the retransmission of lost data until the end of the transmission of the complete data product. In contrast to other multicast transport protocols, MFTP retransmission strategy does not interrupt the fresh data transmission with the retransmissions of older segments. Thanks to this feature, receivers enjoying favourable channel conditions do not suffer from unnecessarily extended transfer delays due to those receivers that experience bad channel conditions. Existing research studies on MFTP's performance over satellite systems assume fixed-capacity satellite uplink channels dedicated to individual clients on the return link. Such fixed-assignment uplink access mechanisms are considered to be too wasteful uses of uplink resources for the sporadic and thin feedback traffic generated by MFTP clients. Indeed, such mechanisms may prematurely limit the scalability of MFTP as the multicast client population size grows. In contrast, the reference satellite system considered in this article employs demand-assignment multiple access (DAMA) with contention-based request signalling on the uplink. DAMA MAC (Medium Access Control) protocols in satellite systems are well-known in the literature for their improved resource utilisation and scalability features. Moreover, DAMA forms the basis for the uplink access mechanisms in prominent satellite networks such as Inmarsat's BGAN (Broadband Global Area Network), and return link specifications such as ETSI DVB-RCS, However, in comparison with fixed-assignment uplink access mechanisms, DAMA protocols may introduce unpredictable delays for MFTP feedback messages on the return link. Collisions among capacity requests on the contention channel, temporary lack of capacity on the reservation channel, and random transmission errors on the uplink are the potential causes of such delays, This article presents the results of a system-level simulation analysis of MFTP over a DAMA GEO satellite system with contention-based request channels. Inmarsat's BGAN system was selected as the reference architecture for analyses. The simulator implements the full interaction between the MFTP server and MFTP clients overlaid on top of the Inmarsat BGAN uplink access mechanism. The analyses aim to evaluate and optimise MFTP performance in Inmarsat BGAN system in terms of transfer delay and system throughput as a function of available capacity, client population size, data product size, channel error characteristics, and MFTP protocol settings. Copyright @ 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.