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Papers by Michael Hadjitheodosiou

Research paper thumbnail of An adaptive multiple-access protocol for an integrated voice and data VSAT network

VSAT (Very Small Aperture Terminal) satellite networks have been successful in providing a variet... more VSAT (Very Small Aperture Terminal) satellite networks have been successful in providing a variety of data communication services to a large number of users. There has been considerable interest recently in transmitting speech as well as data through these networks, and this can only be achieved if existing multiple access protocols are modified so that the different requirements of stream traffic are accommodated. In this paper we propose a possible solution to this problem, using an adaptive reservation scheme over parallel channels. We consider a binary-feedback freeaccess Collision Resolution Algorithm (CRA) over parallel channels, which appears to offer a higher stable throughput and a better delay performance than ALOHAtype reservations previously used in similar situations, without a significant increase in the implementation complexity. VSAT (Very Small Aperture Terminal) satellite networks have been successful in providing a variety of data communication services to a large number of users dispersed over a wide area. There has been considerable interest recently in transmitting speech as well as data through VSAT networks, and thus offer a wider range of services. However, most of the protocols developed so far, are not suitable for stream-type speech traffic. The need to provide low delays and high throughput concurrently, combined with the fact that variable delays co-ordination times imposed by the propagation time of the geostationary satellite link, create a difficult problem for the protocol designer. In this paper we propose a possible solution to this problem, using an adaptive reservation scheme over parallel channels. We consider a binary-feedback free-access Collision Resolution Algorithm (CRA) over parallel channels, which appears to offer a higher stable throughput and a better delay performance than ALOHA-type reservations previously used in similar situations, without a significant increase in the implementation complexity. In ~ef.~ a network architecture based on a demandassigned protocol, using ALOHA for the connection request procedure, was recommended for MSAT-X,, NASA's Land-Mobile Satellite Experiment. This paper focuses on the significant improvements in performance that could be achieved if a new free-access Collision Resolution Algorithm (CRA), derived in ~ef.~, replaces ALOHA for the channel reservation part of the protoco~3.

Research paper thumbnail of Dynamic bandwidth allocation for multimedia traffic in TDMA broadband satellite networks

17th AIAA International Communications Satellite Systems Conference and Exhibit, Feb 23, 1998

A number of satellite systems are currently under development, planning to offer a wide range of ... more A number of satellite systems are currently under development, planning to offer a wide range of traffic services to a large and diverse number of users. In order for these to be financially competitive, the use of the satellite bandwidth, the most expensive component of these systems, needs to be maximized. In this paper we address two ways we can do this. We first discuss a dynamic channel allocation policy, more suitable for a network consisting of a large number of users with fairly limited and changing bandwidth demands. We then develop a Markov Decision Process that could be used to optimize the bandwidth allocation in a broadband TDMA environment and which provides an upper bound for the best allocation policy available. Since the implementation of a computationally intensive and complex optimization policy could prove impractical in a real system, we finally introduce some candidate sub-optimal allocation schemes, that might be less efficient than the optimal, but could prove a lot easier to implement.

Research paper thumbnail of Adaptive multiple access protocols for VSATs providing voice/data services and ATM interconnection

... Two-way communication is established hetween a number of VSATs in a Star configuration, havin... more ... Two-way communication is established hetween a number of VSATs in a Star configuration, having a central Hub acting as the Network Manager Centre (NMC). ... We assume an overall bit rate of 128 Kbitsls for the VSAT-to-Hub connection and 2Mbitsh for Hub-to-VSAT. ...

Research paper thumbnail of Satellite connections for multimedia communications

Research paper thumbnail of B-ISDN implementation via satellite: the CATALYST project

ABSTRACT Presents a simple analysis for the transmission delay across the CATALYST demonstrator n... more ABSTRACT Presents a simple analysis for the transmission delay across the CATALYST demonstrator network, a RACE II project that is intended to demonstrate the applicability of satellite technology for the provision of B-ISDN services. The analysis is based upon a mathematical model and a computer simulation model and describes the end-system to end-system transfer delay depending on message length. The protocol profiles assume a mix of Novell NetWare and Network File System client/server architectures on separate IEEE 802.3 (Ethernet) LANs which are interconnected through ATM/satellite interface units. Areas for further investigation and the implications of the findings on the actual network architecture are discussed

Research paper thumbnail of A case study on optimizing communications for constellation space missions

ABSTRACT A number of NASA future space missions would employ a new topology, consisting of large ... more ABSTRACT A number of NASA future space missions would employ a new topology, consisting of large numbers of distributed, highly coordinated small spacecraft performing a unified scientific observation task. This new class of constellation-based missions will introduce a number of new network control, data management and communication problems that need to be addressed and can provide mission planners with a variety of design trade-offs and additional capabilities in their attempt to satisfy the scientific objectives of their mission. We have started developing a framework for analyzing and studying the operational communication trade-offs for typical constellation mission classes. In this paper we address the communication requirements of constellation space missions in general and, using as an example one mission currently in the planning, the Magnetospheric Multi-Scale mission, we study an appropriate dynamic routing algorithm and list some preliminary simulation model results of the communication link performance. We also discuss ideas about possible future work in this area.

Research paper thumbnail of End-to-end protocol performance in ATM/satellite interconnected LANs

... (131 P. Komisarczuk, M. H. Hadjitheodosiou, F. Coakley, T. Jeans, C. Smythe, “B-ISDN Implemen... more ... (131 P. Komisarczuk, M. H. Hadjitheodosiou, F. Coakley, T. Jeans, C. Smythe, “B-ISDN Implementation Via Satellite: The CATALYST Project”, FIP. First UK WorkshoD on Performance Modelline and Evaluation of ATM Networks. University of Bradford, 28-29th June 1993, pp. ...

Research paper thumbnail of A feedback implosion suppression algorithm for satellite reliable multicast

Research paper thumbnail of Using commercial satellites to provide communication support for space missions

Research paper thumbnail of End-to-end performance analysis for broadband island interconnection via satellite-RACE II/R2074 (Catalyst) project

IET eBooks, Nov 2, 1993

ABSTRACT The authors present an overview of project R2074/Catalyst, an attempt to demonstrate the... more ABSTRACT The authors present an overview of project R2074/Catalyst, an attempt to demonstrate the applicability of satellites in the provision of broadband island interconnection across Europe. This project, which is part of the RACE II initiative, will set up a demonstrator network to implement the interconnection of various LAN architectures. The authors focus on a study of the expected user performance through the Catalyst network based upon mathematical and simulation models. They investigate the performance of a mix of client/server architectures using Novell NetWare and NEtwork File System protocols, which are supported by either the IEEE 802.3/Ethernet LANs, linked via LAN/ATM/satellite interface units. Areas of further investigation, and the implication of the author's analysis on the actual network architecture are discussed

Research paper thumbnail of Efficient and Dynamic Access for the Future NASA Communications Network

22nd AIAA International Communications Satellite Systems Conference & Exhibit 2004 (ICSSC), May 9, 2004

The vision for the future space network involves a scenario where all scientific spacecraft form ... more The vision for the future space network involves a scenario where all scientific spacecraft form a distributed network to provide real-time information transfer to users on the ground. This scenario will require sensors and instruments on spacecraft to become addressable nodes in a ...

Research paper thumbnail of Extending IP Services to Future Space Missions

Research paper thumbnail of TCP In the IPSEC Environment

22nd AIAA International Communications Satellite Systems Conference & Exhibit 2004 (ICSSC), May 9, 2004

Abstract Satellite based networks can transport data for diverse set of applications. Most Intern... more Abstract Satellite based networks can transport data for diverse set of applications. Most Internet applications which use Transmission Control Protocol (TCP) need special handling for efficient operation at high speeds. Recently, support for IPSEC is getting widespread in ...

Research paper thumbnail of IP Multicast via Satellite: A Survey

Research paper thumbnail of Using satellites for providing broadband island interconnection - The RACE II/R2074 (CATALYST) Project

15th International Communicatons Satellite Systems Conference and Exhibit, Feb 28, 1994

Research paper thumbnail of Load balancing in multi-beam satellite systems

Research paper thumbnail of Broadband access via satellite

Computer Networks, Feb 1, 1999

Research paper thumbnail of A pooling & sharing solution for delivering space data using multiple commercial Satcom providers

Research paper thumbnail of Multi-access protocols for a multiservice VSAT network

ABSTRACT We investigate a number of access schemes that, when applied to a VSAT satellite network... more ABSTRACT We investigate a number of access schemes that, when applied to a VSAT satellite network, could accommodate traffic consisting of short, interactive data messages, longer file transfers and voice calls. This will enable a large number of users to share a communications channel. The difficulties associated with the introduction of speech are discussed and ways to deal with these are suggested, so that VSAT systems could provide a wide range of multimedia services to geographically dispersed users

Research paper thumbnail of Next-generation multiservice VSAT networks

Electronics & Communication Engineering Journal, Jun 1, 1997

Research paper thumbnail of An adaptive multiple-access protocol for an integrated voice and data VSAT network

VSAT (Very Small Aperture Terminal) satellite networks have been successful in providing a variet... more VSAT (Very Small Aperture Terminal) satellite networks have been successful in providing a variety of data communication services to a large number of users. There has been considerable interest recently in transmitting speech as well as data through these networks, and this can only be achieved if existing multiple access protocols are modified so that the different requirements of stream traffic are accommodated. In this paper we propose a possible solution to this problem, using an adaptive reservation scheme over parallel channels. We consider a binary-feedback freeaccess Collision Resolution Algorithm (CRA) over parallel channels, which appears to offer a higher stable throughput and a better delay performance than ALOHAtype reservations previously used in similar situations, without a significant increase in the implementation complexity. VSAT (Very Small Aperture Terminal) satellite networks have been successful in providing a variety of data communication services to a large number of users dispersed over a wide area. There has been considerable interest recently in transmitting speech as well as data through VSAT networks, and thus offer a wider range of services. However, most of the protocols developed so far, are not suitable for stream-type speech traffic. The need to provide low delays and high throughput concurrently, combined with the fact that variable delays co-ordination times imposed by the propagation time of the geostationary satellite link, create a difficult problem for the protocol designer. In this paper we propose a possible solution to this problem, using an adaptive reservation scheme over parallel channels. We consider a binary-feedback free-access Collision Resolution Algorithm (CRA) over parallel channels, which appears to offer a higher stable throughput and a better delay performance than ALOHA-type reservations previously used in similar situations, without a significant increase in the implementation complexity. In ~ef.~ a network architecture based on a demandassigned protocol, using ALOHA for the connection request procedure, was recommended for MSAT-X,, NASA's Land-Mobile Satellite Experiment. This paper focuses on the significant improvements in performance that could be achieved if a new free-access Collision Resolution Algorithm (CRA), derived in ~ef.~, replaces ALOHA for the channel reservation part of the protoco~3.

Research paper thumbnail of Dynamic bandwidth allocation for multimedia traffic in TDMA broadband satellite networks

17th AIAA International Communications Satellite Systems Conference and Exhibit, Feb 23, 1998

A number of satellite systems are currently under development, planning to offer a wide range of ... more A number of satellite systems are currently under development, planning to offer a wide range of traffic services to a large and diverse number of users. In order for these to be financially competitive, the use of the satellite bandwidth, the most expensive component of these systems, needs to be maximized. In this paper we address two ways we can do this. We first discuss a dynamic channel allocation policy, more suitable for a network consisting of a large number of users with fairly limited and changing bandwidth demands. We then develop a Markov Decision Process that could be used to optimize the bandwidth allocation in a broadband TDMA environment and which provides an upper bound for the best allocation policy available. Since the implementation of a computationally intensive and complex optimization policy could prove impractical in a real system, we finally introduce some candidate sub-optimal allocation schemes, that might be less efficient than the optimal, but could prove a lot easier to implement.

Research paper thumbnail of Adaptive multiple access protocols for VSATs providing voice/data services and ATM interconnection

... Two-way communication is established hetween a number of VSATs in a Star configuration, havin... more ... Two-way communication is established hetween a number of VSATs in a Star configuration, having a central Hub acting as the Network Manager Centre (NMC). ... We assume an overall bit rate of 128 Kbitsls for the VSAT-to-Hub connection and 2Mbitsh for Hub-to-VSAT. ...

Research paper thumbnail of Satellite connections for multimedia communications

Research paper thumbnail of B-ISDN implementation via satellite: the CATALYST project

ABSTRACT Presents a simple analysis for the transmission delay across the CATALYST demonstrator n... more ABSTRACT Presents a simple analysis for the transmission delay across the CATALYST demonstrator network, a RACE II project that is intended to demonstrate the applicability of satellite technology for the provision of B-ISDN services. The analysis is based upon a mathematical model and a computer simulation model and describes the end-system to end-system transfer delay depending on message length. The protocol profiles assume a mix of Novell NetWare and Network File System client/server architectures on separate IEEE 802.3 (Ethernet) LANs which are interconnected through ATM/satellite interface units. Areas for further investigation and the implications of the findings on the actual network architecture are discussed

Research paper thumbnail of A case study on optimizing communications for constellation space missions

ABSTRACT A number of NASA future space missions would employ a new topology, consisting of large ... more ABSTRACT A number of NASA future space missions would employ a new topology, consisting of large numbers of distributed, highly coordinated small spacecraft performing a unified scientific observation task. This new class of constellation-based missions will introduce a number of new network control, data management and communication problems that need to be addressed and can provide mission planners with a variety of design trade-offs and additional capabilities in their attempt to satisfy the scientific objectives of their mission. We have started developing a framework for analyzing and studying the operational communication trade-offs for typical constellation mission classes. In this paper we address the communication requirements of constellation space missions in general and, using as an example one mission currently in the planning, the Magnetospheric Multi-Scale mission, we study an appropriate dynamic routing algorithm and list some preliminary simulation model results of the communication link performance. We also discuss ideas about possible future work in this area.

Research paper thumbnail of End-to-end protocol performance in ATM/satellite interconnected LANs

... (131 P. Komisarczuk, M. H. Hadjitheodosiou, F. Coakley, T. Jeans, C. Smythe, “B-ISDN Implemen... more ... (131 P. Komisarczuk, M. H. Hadjitheodosiou, F. Coakley, T. Jeans, C. Smythe, “B-ISDN Implementation Via Satellite: The CATALYST Project”, FIP. First UK WorkshoD on Performance Modelline and Evaluation of ATM Networks. University of Bradford, 28-29th June 1993, pp. ...

Research paper thumbnail of A feedback implosion suppression algorithm for satellite reliable multicast

Research paper thumbnail of Using commercial satellites to provide communication support for space missions

Research paper thumbnail of End-to-end performance analysis for broadband island interconnection via satellite-RACE II/R2074 (Catalyst) project

IET eBooks, Nov 2, 1993

ABSTRACT The authors present an overview of project R2074/Catalyst, an attempt to demonstrate the... more ABSTRACT The authors present an overview of project R2074/Catalyst, an attempt to demonstrate the applicability of satellites in the provision of broadband island interconnection across Europe. This project, which is part of the RACE II initiative, will set up a demonstrator network to implement the interconnection of various LAN architectures. The authors focus on a study of the expected user performance through the Catalyst network based upon mathematical and simulation models. They investigate the performance of a mix of client/server architectures using Novell NetWare and NEtwork File System protocols, which are supported by either the IEEE 802.3/Ethernet LANs, linked via LAN/ATM/satellite interface units. Areas of further investigation, and the implication of the author's analysis on the actual network architecture are discussed

Research paper thumbnail of Efficient and Dynamic Access for the Future NASA Communications Network

22nd AIAA International Communications Satellite Systems Conference & Exhibit 2004 (ICSSC), May 9, 2004

The vision for the future space network involves a scenario where all scientific spacecraft form ... more The vision for the future space network involves a scenario where all scientific spacecraft form a distributed network to provide real-time information transfer to users on the ground. This scenario will require sensors and instruments on spacecraft to become addressable nodes in a ...

Research paper thumbnail of Extending IP Services to Future Space Missions

Research paper thumbnail of TCP In the IPSEC Environment

22nd AIAA International Communications Satellite Systems Conference & Exhibit 2004 (ICSSC), May 9, 2004

Abstract Satellite based networks can transport data for diverse set of applications. Most Intern... more Abstract Satellite based networks can transport data for diverse set of applications. Most Internet applications which use Transmission Control Protocol (TCP) need special handling for efficient operation at high speeds. Recently, support for IPSEC is getting widespread in ...

Research paper thumbnail of IP Multicast via Satellite: A Survey

Research paper thumbnail of Using satellites for providing broadband island interconnection - The RACE II/R2074 (CATALYST) Project

15th International Communicatons Satellite Systems Conference and Exhibit, Feb 28, 1994

Research paper thumbnail of Load balancing in multi-beam satellite systems

Research paper thumbnail of Broadband access via satellite

Computer Networks, Feb 1, 1999

Research paper thumbnail of A pooling & sharing solution for delivering space data using multiple commercial Satcom providers

Research paper thumbnail of Multi-access protocols for a multiservice VSAT network

ABSTRACT We investigate a number of access schemes that, when applied to a VSAT satellite network... more ABSTRACT We investigate a number of access schemes that, when applied to a VSAT satellite network, could accommodate traffic consisting of short, interactive data messages, longer file transfers and voice calls. This will enable a large number of users to share a communications channel. The difficulties associated with the introduction of speech are discussed and ways to deal with these are suggested, so that VSAT systems could provide a wide range of multimedia services to geographically dispersed users

Research paper thumbnail of Next-generation multiservice VSAT networks

Electronics & Communication Engineering Journal, Jun 1, 1997