Institute for Systems Research Technical Reports
Permanent URI for this collectionhttp://hdl.handle.net/1903/4376
This archive contains a collection of reports generated by the faculty and students of the Institute for Systems Research (ISR), a permanent, interdisciplinary research unit in the A. James Clark School of Engineering at the University of Maryland. ISR-based projects are conducted through partnerships with industry and government, bringing together faculty and students from multiple academic departments and colleges across the university.
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Item Improving TCP Performance over High-Bandwidth Geostationary Satellite Links(1999) Bharadwaj, Vijay G.; Baras, John S.; ISR; CSHCNThe Transmission Control Protocol (TCP) is the most widely used transportprotocol in the Internet today. The problem of poor TCP performance oversatellite networks has recently received much attention, and much work hasbeen done in characterizing the behavior of TCP and proposing methods forimprovement. Meanwhile it remains hard to upgrade the majority of legacyhost and gateway systems in the Internet that are running old and outdatedsoftware so that they can perform better in the changing networks of today.In this thesis we consider an alternative network architecture, where largeheterogeneous networks are built from small homogeneous networksinterconnected by carefully designed proxy systems. We describe the designand implementation of such a proxy and demonstrate marked performanceimprovements over both actual and simulated satellite channels. We alsodiscuss some benefits and drawbacks of using proxies in networks andexplore some tradeoffs in proxy design.
Item Hybrid Internet Simulation Testbed(1999) Liu, Mingyan D.; Karir, Manish; Raissi-Dehkordi, Majid; Baras, John S.; Baras, John S.; ISR; CSHCNInternet technology as a widely accepted modern telecommunicationstandard has been widely extended to combine with numerous othertechnologies, e.g., satellite, ATM, wireless. This is whatwe term Hybrid Internet. Along with this technology emerging,various enhancements and alterations of standard TCP/IP for differentpurposes have been proposed and studied intensively. More and morefrequently we are facing the question of how to choose from thesedifferent schemes to design a system for a particular purpose, whichwould inevitably involve the interaction and trade-off study. We believethat simulation is a powerful tool for this type of work.In this paper, we describeour implementation of a Hybrid Internet testbed which includesa series of traffic models and TCP/IP enhancements.The goal of our work is to makea set of reusable modules upon which we can build complex systemsto study the standard protocols and their variations.We also present application examples using these module components.Item An Architecture for Internet Service via Broadband Satellite Networks(1999) Bharadwaj, Vijay G.; Baras, John S.; Butts, Norman P.; Baras, John S.; ISR; CSHCNHigh bandwidth satellites hold out the promise of a rapidly deployablecommunications infrastructure with a natural support for mobility. However,the Transmission Control Protocol (TCP), widely used in the Internet, performspoorly over satellite links, and this presents an obstacle to thedeployment of such systems. We present an architecture that overcomesthese problems and provides an approach to building complex heterogeneousnetworks from simple units. We also present some results from our initialimplementation, which uses TCP connection splitting to improve TCPperformance over satellite links.Item Simulation Studies of a Hybrid Network in Order to Enhance the Performance of Hybrid Internet Service(1998) Gaid, Ahmed Y.; Baras, John S.; ISR; CSHCNThe work reported here addresses the modeling and simulation of a hybrid network that conforms to Hybrid Internet Service, which is an Internet access currently commercialized by Hughes Network Systems. The objective is to research and discover performance enhancement techniques for Hybrid Internet Service. Hybrid Internet Service intends to provide Internet end users with high bandwidth by delivering packets over a satellite channel. It takes advantage of the fact that the vast majority of Internet end-users don't send as much data as they receive. However, long delays experienced over the satellite channel (in the case of a GEO satellite) have catastrophic consequences on the overall throughput with Commercial-Off-The-Shelf TPC/IP stacks. This problem is addressed by the Asymmetric TCP/IP protocol implemented within a gateway, the hybrid gateway. The hybrid gateway acts as a go-between for the server and the end user. The hybrid gateway both acknowledges packets on behalf of the end user and advertises a larger window to the server. We have implemented the Asymmetric TCP/IP within the hybrid gateway with OPNET, which is an industrial-strength, popular network modeling and simulation software. A discussion of the current results of the simulation in the broader perspective of hybrid networks development is provided following the presentation of both Hybrid Internet Service and OPNET along with the various built-in OPNET models used in the course of the simulation. The methodology we have followed is also included in this report.Item Asymmetric Internet Access over Satellite-Terrestrial Networks(1996) Arora, Vivek; Suphasindhu, N.; Baras, John S.; Dillon, Douglas; ISR; CSHCNDirecPCtm's Turbo Internet is a low-cost hybrid (satellite- terrestrial) high-speed digital transmission system developed as a collaborative effort between the Center for Satellite and Hybrid Communication Networks and Hughes Network Systems. The system uses receive-only satellite links for downstream data delivery and public telephone networks at the modem speeds to provide the upstream communications path. One of the services provided is high speed Internet access based on an asymmetric TCP/IP protocol. Our principle object is to lower cost and efficiently provide high bandwidth access to Internet services such as file transfer, the World Wide Web, and the MBONE. In the initial protocol implementation, we achieved four times higher throughput than that of Today's high-speed modems (28.8 Kbps) alone2. This throughput can be further enhanced. The mismatch in bandwidth and delay in this hybrid network prevents the full use of the satellite link bandwidth (1 Mbps). This paper presents two techniques, TCP spoofing and selective acknowledgement dropping, which significantly increase the overall throughput of the hybrid network. Our approach does not require any modification to the TCP/IP protocol stacks on the end hosts. The solutions proposed in this paper could be used to improve TCP/IP performance of other hybrid networks which have the disadvantage of high bandwidth-delay products and/or low bandwidth return paths. Furthermore, we are investigating how to extend IP multicast services to such hybrid networks. The broadcast nature of Satellite communication makes it an efficient way for high- bandwidth multicast transmission.- A revised version of this technical report has been published in
Proceedings of the AIAA: 16th International Communications Satellite Systems Conference and Exhibit, Part 1, pp. 476-482, Washington, D.C., February 25-29, 1996.Item Effective Extensions of Internet in Hybrid Satellite-Terrestrial Networks(1996) Arora, Vivek; Suphasindhu, N.; Baras, John S.; Dillon, Douglas; ISR; CSHCNDirect PCTM's Turbo Internet is a low-cost hybrid (satellite- terrestrial) high-speed digital transmission system developed as a collaborative effort between the Center for Satellite and Hybrid Communication Networks and Hughes Network Systems. The system uses receive-only VSAT satellite links for downstream data delivery and public telephone networks at modem speeds to provide the upstream communications path. One of the services provided is high speed Internet access based on an asymmetric TCP/IP protocol. In the initial protocol implementation, we achieved four times higher throughput than that of today high-speed modems (28.8 Kbps) alone (Falk 1995). This throughput can be further enhanced. The mismatch in bandwidth and delay in this hybrid network prevents the full use of the satellite link bandwidth (1 Mbps). This paper presents two techniques. TCP spoofing and selective acknowledgement dropping, which significantly increase the overall throughput of the hybrid network. Our approach does not require any modification to the TCP/IP protocol stacks on the end hosts. The solutions proposed in this paper could be used to improve TCP/IP performance of other hybrid networks which have the disadvantage of high bandwidth-delay products and/or low bandwidth return paths.- A revised version of this report has been published in
Proceedings of the 1st Conference of Commercial Development of Space, Part One, pp. 339-344, Albuquerque, New Mexico, January 7-11, 1996.Item A System Design for a Hybrid Network Data Communications Terminal Using Asymmetric TCP/IP to Support Internet Applications(1994) Falk, Aaron D.; Baras, John S.; ISR; CSHCNAccess to the Internet is either too slow (e.g. dial-up SLIP) or too expensive (e.g. switched 56 kbps, frame relay) for the home user or small enterprise. The Center for Satellite and Hybrid Communication Networks and Hughes Network Systems have collaborated using system integration principles to develop a prototype of a low-cost hybrid (dial-up and satellite) network terminal which can deliver data from the Internet to the user at rates up to 160 kbps. An asymmetric TCP/IP connection is used breaking the network link into two physical channels: a terrestrial dial-up link for carrying data from the terminal into the Internet and a receiver-only satellite link carrying IP packets from the Internet to the user. With a goal of supporting bandwidth hungry Internet applications such as Mosaic Gopher, and FTP, this system has been designed to support any Intel 80386/486 PC, any commercial TCP/IP package, any unmodified host on the Internet, and any of the routers, etc. within the Internet. The design exploits the following three observations: 1) satellites are able to offer high bandwidth connections to a large geographical area, 2) a receiver-only VSAT is cheap to manufacture and easier to install than one which can also transmit, and 3) most computer users, especially those in a home environment, will want to consume much more data than they generate. IP encapsulation, or tunneling, is used to manipulate the TCP/IP protocols to route packets asymmetrically.