Communication Research CenterAcknowledgementBandwidth Allocation and Management for Multimedia Networks Over Satellite LinksCharles Auger, Peter Andreadis, Claude Bélisle, and Steve BernierCommunication Research Center Ottawa, Ontario, Canada E-mail: [email protected] paper presents a dynamic bandwidth allocation andmanagement technique based on flow analysis and quality ofservice provisioning. This technique aims at improving theperformance and bandwidth utilization of various multimediaapplications over long-delay satellite links. A networkconfiguration using satellite communication resources andproviding e-mail, web browsing, file transfer and databaseservices has been modeled using OPNET 7.0. A dynamicbandwidth allocation scheme combined with a weighted-fair-queuing (WFQ) algorithm has been implemented in thenetwork model. Network configuration, and implementationdetails are discussed.1. INTRODUCTIONThe ubiquitous nature of satellite communications makes it anideal candidate for providing Internet services worldwide. Theadvantages of combining the high bandwidth, wide areacoverage, reconfigurability, and multicast capabilities ofsatellites with terrestrial networks provide immense newmarket opportunities. Users can be connected to the satellitelink directly from their home or mobile terminal, via a localarea network or through an Internet gateway. This architecturecreates a wide variety of bandwidth requirements at thedifferent satellite communication ground terminals (GT).Considering the expensiveness of satellite bandwidth, atechnique to effectively share it between the different GTs isneeded. In this paper, such a technique allowing dynamic bandwidthallocation is presented. It has been developed in the context ofa controlled network environment, where our client hasknowledge and control over the types of traffic and thenetwork applications. Consequently, traffic can be categorizedin flows according to some pre-determined rules, and prioritiescan be assigned to each flow. The quality of service offered tousers is therefore related to the bandwidth allocation schemeand the prioritization mechanisms. Section 2 of the paper presents the network configuration usedin this study and introduces the modifications done to thecommunication protocol in order to improve performance andbandwidth utilization. Section 3 describes the dynamicbandwidth allocation scheme. Section 4 deals with the use ofthe WFQ queuing mechanism and explains the modificationsdone to it to support dynamic bandwidth allocation. Someclosing remarks and directions for future work are presented insection 5.2. MODEL DESCRIPTIONThe project described in this paper is composed of two distincttasks. The first one consists of evaluating the performance ofour client’s applications when part of the network travelsthrough a geo-synchronous satellite constellation. This hasbeen accomplished by modeling the networks using OPNETand evaluating the performance through simulations. Asummary of the OPNET design is presented in section 2.1.The second task of the project consists of proposing andevaluating ways to improve the performance of the networkapplications traveling through the satellite links. The potentialimprovements we considered are presented in section 2.2 andthe modifications made to our OPNET models to support thoseimprovements are described in section 2.3.2.1 Original Network ConfigurationTwo subnets linked via satellite are modeled using the OPNET7.0 software. The subnets contain two networks, one located inOttawa, called CRC Ottawa, and the other in Europe, calledSamos U (Figure 1). The Samos U network contains Lans andworkstations running various applications that request datafrom the CRC Ottawa network. Each ground terminal is allocated dedicated bandwidth tocommunicate over the satellite link. The links shown hereemulate a satellite connection with various delays. Thesatellite payload is designed as a simple router at this point.No physical waveform or satellite processing is modeled atthis time. The RF characteristics are modeled as link qualityexpressed in terms of BER.All traffic generated travels over the satellite link. No cachingis performed. The application data sent are file transfers (FTP),web (HTTP), e-mail, database and weather informationdownloads (HTTP based application). Traffic models wheredeveloped using the Profile and Application configurationtools of OPNET. Many simulations were performed for threetypes of TCP stacks, and for different bandwidthapportionments under various BER.1Figure1. Satellite Network in OPNETFrom the simulation results, two major issues can be raised.First, as expected, the network performance is greatlyinfluenced by the TCP implementation and even with the bestimplementation available performance results are stillmarginal over long delay links. Second, to obtain goodresponse time, the apportioned bandwidth should be madeequal to four times the average traffic throughput. While thisis not a costly issue for terrestrial networks, in a satelliteenvironment, where bandwidth is an expensive resource, abetter utilization than 4-to-1 would be desirable. For moredetails of the network simulations performed and the results,refer to “Performance Analysis of Multimedia Networks overSatellite Links”, by P. Andreadis[1].2.2 Improvement Areas Three possible performance improvements to our networkconfiguration have been considered. First, TCP enhancementshave been analyzed in order to improve the performance ofTCP based applications over long-delay error prone links. Thetopic of TCP performance issues and possible improvementsover satellite links is presented in [2]. The second potential improvement concerns the allocation ofbandwidth. The expense of satellite communication resourcesrenders static bandwidth apportionment cost ineffective [3].Furthermore, traditional circuit-switched based allocationmethods are inadequate to