Abstract-Several satellite systems currently in operation or under development claim to support broadband Internet applications. In these scenarios, transmission control protocol (TCP) plays a critical role. Unfortunately, when used with satellite links, TCP suffers from a number of well-known performance problems, especially for higher data rates and high altitude satellites with longer delays. In response to these difficulties, the satellite and Internet research communities have developed a large gamut of solutions ranging from architectural modifications to changes in the TCP protocol. Among these, one approach requiring minimal modifications involves splitting the TCP connection in two or more segments with one segment connecting terrestrial nodes across the satellite network. In this paper, we consider an evolution of this idea: placing a TCP proxy on board the satellite that further subdivides the end-to-end connection into separate TCP connections between ground and space. We focus upon the efficient use of buffer resources on board the satellite, while at the same time enhancing TCP performance. We evaluate two TCP protocol versions, TCP NewReno and TCP Westwood. We consider various geosynchronous earth orbit satellite scenarios, with and without the split proxy, and with different channel error conditions (random errors, shadowing, etc). Using simulation, we show that an on-board proxy provides a number of distinct advantages and can enhance throughput up to threefold for both TCP New Reno and TCP Westwood, in some scenarios, with relatively modest on-board buffering requirements. The main contributions of this paper are: the on-board split proxy concept, the buffer management strategy, the use of a realistic "urban shadowing" model in the evaluation, and the extensive comparison of the recently announced TCP Westwood with the traditional TCP New Reno.

In grid computing environments, network bandwidth discovery and allocation is a serious issue. Before their applications are running, grid users will need to choose hosts based on available bandwidth. Running applications may need to adapt to a changing set of hosts. Hence, a tool is needed for monitoring network performance that is integral to the grid environment. To address this need, Gloperf was developed as part of the Globus grid computing toolkit. Gloperf is designed for ease of deployment and makes simple, end-to-end TCP measurements requiring no special host permissions. Scalability is addressed by a hierarchy of measurements based on group membership and by limiting overhead to a small, acceptable, fixed percentage of the available bandwidth. Since this fixed overhead may push host-pair revisit time into the tens-of-hours, we also quantitatively examine the "trajectory" of the cost-error trade-off for measurement frequency.

Abstract. The use of HAPS/UAV to enhance telecommunication capabilities has been proposed as an effective solution to support hot spot communications in limited areas. To ensure communication capabilities even in case of emergency (earthquake, power blackout, chemical/nuclear disaster, terrorist attack), when terrestrial fixed and mobile infrastructures are damaged or become unavailable, the access to satellites represents a reliable solution with worldwide coverage, even though it may suffer from shadowing impairment, especially in an urban environment. In this paper we approach an innovative and more challenging architecture foreseeing HAPS/UAV connected to the satellite in order to enlarge coverage and to allow interconnection with very remote locations. In this scenario, we have analysed TCP-based applications proposing some innovative techniques, both at protocol and at architectural level, to improve performance. In particular, we propose the use of a PEP technique, namely splitting, to speed up window growth in spite of high latency, combined with TCP Westwood as a very efficient algorithm particularly suitable and well performing over satellite links.

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