DRUM :: Browsing by Author "Hadjitheodosiou, Michael H."

Browsing by Author "Hadjitheodosiou, Michael H."

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Alternative Network Architectures for Supporting Communications from the International Space Station
(2002) Nguyen, Alex T.; Hadjitheodosiou, Michael H.; Baras, John S.; ISR; CSHCN
In order to support the communications needs of the International Space Station (ISS), alternative communications architectures to provide broadband support need to be considered. We address three communications options and evaluate an architecture for the direct to ground option, which could serve as an intermediary solution to satisfy near term communications needs of commercial experiments and payloads on the ISS and overcome certain limitations of the current ISS communications infrastructure. We focus on a particular user requirements, and examine the system communications links, and coverage availability. These parameters, along with high-level cost estimates, are compared to using commercial relay satellites, and an enhanced TDRSS. The direct to ground option is viable for store-and-forward applications and cost comparable to commercial constellations, but TDRSS is the choice for real-time or continuous data applications.
Broadband Access via Satellite
(1999) Hadjitheodosiou, Michael H.; Ephremides, Anthony; Friedman, Daniel E.; Ephremides, A.; ISR; CSHCN
Satellites are well suited for broadband communications. In this paperwe consider the special features of satellite systems, some of thebroadband applications that are well-suited for satellites and someof the technologies which make possible broadband satellitecommunications, as well as the research programs that led to theirdevelopment. We describe how such technologies, and other factors,have contributed to the evolution of broadband satellite systems,and discuss some of the challenges in establishing such systems.We finish by offering some concluding remarks on the role ofsatellites for broadband access.
The research and scientific content in this material hasbeen published in Computer Networks, vol. 31, pp. 353-378, 1999.
A direct-to-ground architecture for supporting Commercial Communications from the International Space Station
(2002) Nguyen, Alex T.; Zhou, X.; Hadjitheodosiou, Michael H.; Baras, John S.; ISR; CSHCN
We outline the first steps of an effort to start defining a communications architecture for supporting broadband data communications from the International Space Station. We address three communications options and focus on a direct-to-ground architecture, which could serve as an intermediary solution to satisfy near term communications needs of commercial experiments and payloads on the ISS and overcome certain limitations of the current ISS communications infrastructure. A high-level analysis of the architecture for the direct to ground option is performed, focusing on a particular user requirements, communications links, and coverage availability. We also discuss system, mobility support and protocol issues that need to be addressed for this solution to be a feasible alternative.
Extending IP Services to Future Space Missions
(2001) Hadjitheodosiou, Michael H.; Nguyen, Alex T.; ISR; CSHCN
We outline the first steps of an effort to start defining the communication architecture for the next generation of space missions that will support NASA's "faster, better, cheaper" concept and will enable new types of collaborative science, where investigators can access their data from space "anytime, anywhere" via direct communication with the instruments on the spacecraft.
We discuss the building blocks for a conceptual design of a network architecture that could support and take advantage of IP-capable spacecraft.
We show that access from a large number of ground stations (that could be directly connected to the existing Internet infrastructure) could increase spacecraft availability time by a significant factor.
We discuss possible multiple access techniques that could enable the transition to an on-demand operation, where spacecraft share space spectrum dynamically. We calso discuss the particular requirements of a next generation of missions consisting of constellations of several small spacecraft and introduce a number of new complex network control, scheduling, routing, data management and communication problems that need to be addressed for this topology.
A Feedback Implosion Suppression Algorithm for Satellite Reliable Multicast
(2003) Akkor, Gun; Baras, John S.; Hadjitheodosiou, Michael H.; Baras, John S.; ISR; CSHCN
In this paper, we propose a knapsack-based feedback suppressionalgorithm for reliable multicast transport protocols operating over asatellite network. A reliable transport protocol needs to identify thepackets which failed to reach a given destination. This is achievedthrough feedback packets returned to the source. For multicastservices, receiver feedback has been shown to lead to thefeedback implosion problem. Feedback implosion is awell-studied problem and various solutions exist in the literature.However, these solutions mainly focus on wireline terrestrial networksand do not take into account the inherent characteristics of thesatellite channel and the architecture of the deployed network.Therefore, we need to revisit the problem and provide a new set ofsolutions for efficient integration to next generation satellitesystems. In this paper, we introduce a feedback implosion suppressionalgorithm, which effectively suppresses the amount of feedback relayedthrough the satellite channel, while ensuring that the criticalinformation is conveyed in a timely fashion. The performance of thealgorithm is evaluated through simulations.
HYBRID NETWORKS WITH A SPACE SEGMENT - TOPOLOGY DESIGN AND SECURITY ISSUES
(2005) Roy-Chowdhury, Ayan; Baras, John S.; Hadjitheodosiou, Michael H.; Rentz, Nicolas; Baras, Dr. John S.; ISR; CSHCN
In this paper we investigate a hybrid network topology that is suitable for supporting interplanetary communications. We define an architecture comprised of a network of sensor nodes on a remote planetary surface, connected to a hybrid terrestrial network of wired and wireless LANs through a series of satellite relays. All the nodes in the network are IPaddressable and support public and symmetric key cryptography. The resulting network forms a hierarchical hybrid mesh that connects users on Earth to networks on or around a remote planetary surface. We describe the design of the network and present preliminary simulation results illustrating the network performance for various parameters. We also discuss how algorithms for user authentication, message integrity and data confidentiality can be incorporated in the network infrastructure for secure end-to-end communication.
IP Multicast via Satellite: A Survey
(2003) Akkor, Gun; Hadjitheodosiou, Michael H.; Baras, John S.; Baras, John S.; ISR; CSHCN
Many of the emerging applications in the Internet, such astele-conferencing, distance-learning, distributed games, softwareupdates, and distributed computing would benefit from multicastservices. In many of these applications, there is a need todistribute information to many sites that are widely dispersed fromeach other. Communication satellites are a natural technology optionand are extremely well suited for carrying such services. Despite thepotential of satellite multicast, there exists little support forsatellite IP multicast services. Both Internet Engineering andInternet Research Task Forces (IETF and IRTF) have been involved in aresearch effort to identify the design space for a general purposereliable multicast protocol and standardize certain protocolcomponents as emph{building blocks}. However, for satellitemulticast services, several of these components have a differentdesign space. In this paper, we attempt to provide an overview of thedesign space and the ways in which the network deployment andapplication requirements affect the solution space. We maintain asimilar taxonomy to that of the IETF efforts, and identify which keycomponents of a general multicast protocol are affected by two of themost common satellite network deployment scenarios. We also highlightsome of the issues which we think are critical in the development ofnext generation satellite IP multicast services.
IP Multicast via Satellite: A Survey
(2002) Akkor, Gun; Hadjitheodosiou, Michael H.; Baras, John S.; Baras, John S.; ISR; CSHCN
Many of the emerging applications in the Internet, such astele-conferencing, distance-learning, distributed games, softwareupdates, and distributed computing would benefit from multicastservices. In many of these applications, there is a need todistribute information to many sites that are widely dispersed fromeach other. Communication satellites are a natural technology optionand are extremely well suited for carrying such services. Despite thepotential of satellite multicast, there exists little support forsatellite IP multicast services. Both Internet Engineering andInternet Research Task Forces (IETF and IRTF) have been involved in aresearch effort to identify the design space for a general purposereliable multicast protocol and standardize certain protocolcomponents as building blocks. However, for satellite multicastservices, several of these components have a different designspace. In this paper, we attempt to provide an overview of the designspace and the ways in which the network deployment and applicationrequirements affect the solution space. We maintain a similartaxonomy to that of the IETF efforts, and identify which keycomponents of a general multicast protocol are affected by two of themost common satellite network deployment scenarios. We also highlightsome of the issues which we think are critical in the development ofnext generation satellite IP multicast services.
Load balancing in multi-beam satellite systems
(2004) Akkor, Gun; Baras, John S.; Hadjitheodosiou, Michael H.; Baras, John S.; ISR; CSHCN
We propose an approach to optimize resource sharing and in a multi-beam broadband satellite system that supports both unicast and multicast flows. We show that in this architecture, the load on every spot-beam queue could be different, depending on the type of the flows and the distribution of the receivers across spot-beam coverage areas. This load unbalance may significantly under-utilize the system resources and decrease the system throughput when both unicast and multicast flows are active in the system. In this paper, we formulate an optimization problem for intra- and inter-beam resource sharing such that the variance of the session rates experienced by users of a flow located in different beam coverage areas is minimized. The result of our resource allocation also determines the maximum sustainable rate of each flow. We calculate the beam utilization and maximum sustainable sessions rates with and without optimization and compare the results. We conclude that this method significantly improves the session rates and overall utilization of the system when both unicast and multicast flows are active.
Multicast-aware Power Allocation in Multiple Spot-Beam Satellite Communication Systems
(2004) Akkor, Gun; Baras, John S.; Hadjitheodosiou, Michael H.; Baras, John S.; ISR; CSHCN
We address the problem of optimizing resource sharing and flow control in a multiple spot-beam broadband satellite system that supports both unicast and multicast flows. Satellite communication systems, with their wide-area coverage and direct access to large number of users, clearly have an inherent advantage in supporting multicast applications. In order to remain competitive against other broadband technologies, however, next generation satellite systems will be required to support both unicast and multicast flows and offer optimal sharing of system resources between these flows. We show that, in a multiple spot-beam system, a high load variation across spot-beam queues may force lower allocated session rates for active flows, and be perceived as unsatisfactory by potential users when both unicast and multicast flows are active in the system. We propose an optimization framework for balancing the spot-beam queue service rates such that the sum of the rate variances of all active multicast flows is minimized. This is achieved through the re-distribution of system power among spot-beam queues, by taking into account the load on the queues and the channel states. We conclude that it is possible to increase the average session rates of multicast flows by up to 16%, and the rates of unicast flows by up to 4% after this optimization is applied.
A Multiple Subset Sum Formulation for Feedback Implosion Suppression over Satellite Networks
(2004) Akkor, Gun; Baras, John S.; Hadjitheodosiou, Michael H.; Baras, John S.; ISR; CSHCN
In this paper, we present a feedback implosion suppression (FIS) algorithm that reduces the volume of feedback information transmitted through the network without relying on any collaboration between users, or on any infrastructure other than the satellite network. Next generation satellite systems that utilize the Ka frequency band are likely to rely on various fade mitigation (compensation) techniques ranging from adaptive coding to dynamic power control, in order to guarantee a service quality that is comparable to other broadband technologies. User feedback would be a valuable input for a number of such components, however, collecting periodic feedback from a large number of users would result in the well-known feedback implosion problem. Feedback implosion is identified as a major problem when a large number of users try to transmit their feedback messages through the network, holding up a significant portion of the uplink resources and clogging the shared uplink medium. In this paper, we look at a system where uplink channel access is organized in time-slots. The goal of the FIS algorithm is to reduce the number of uplink time-slots hold up for the purpose of feedback transmission. Our analysis show that the FIS algorithm effectively suppresses the feedback messages of 95% of all active users, but still achieves acceptable performance results when the ratio of available time-slots to number of users is equal to or higher than 5%.
Power Balancing in Multiple Spot-Beam Satellite Systems for Multicast Support
(2004) Akkor, Gun; Baras, John S.; Hadjitheodosiou, Michael H.; Baras, John S.; ISR; CSHCN
We address the problem of optimizing resource sharing and flow control in a multiple spot-beam broadband satellite system that supports both unicast and multicast flows. Satellite communication systems, with their wide-area coverage and ubiquitous access to large number of users, clearly have an inherent advantage in supporting distributed applications that require concurrent transmission of content to multiple users. In order to remain competitive against other broadband technologies, next generation satellite systems will be required to support both unicast and multicast flows and offer optimal sharing of system resources between these flows. We show that a high load variation across the spot-beam queues may significantly under-utilize the system and be perceived unsatisfactory by potential users when both unicast and multicast flows are active in the system. We propose an optimization based-approach to balance the load in the system and conclude that it is possible to increase the average session rates of all active flows by up to 30% after this optimization is applied.
A Reliable Multicast Transport Protocol for Satellite Communication Systems
(2003) Akkor, Gun; Baras, John S.; Hadjitheodosiou, Michael H.; Baras, John S.; ISR; CSHCN
In this paper, we propose a reliable multicast transport protocol for satellite communication systems. Many of the emerging applications in the Internet would benefit from reliable multicast services, and broadband satellite communication systems have attractive characteristics for supporting such services. However, many of the protocols designed primarily for terrestrial networks do not perform well over satellite networks. Therefore, it is necessary to look at the problem of reliable multicast in the solution space of satellite communications. Our protocol makes use of a special form of forward error correcting codes and couples it with an adaptive window based control mechanism to dynamically adjust the number of encoding packets forwarded to the users. Protocol makes very good use of the broadcast nature of the satellite channel and attempts to minimize the feedback from users. We evaluate the protocol performance by extensive computer simulations.
Security Issues in Hybrid Satellite Networks
(2004) Roy-Chowdhury, Ayan; Hadjitheodosiou, Michael H.; Baras, John S.; Baras, John S.; ISR; CSHCN
Satellites are expected to play an increasingly important role in providing broadband Internet services over long distances in an efficient manner. Future networks will be hybrid in nature - having terrestrial nodes interconnected by satellite links. Security is an important concern in such networks, since the satellite segment is susceptible to a host of attacks including eavesdropping, session hijacking and data corruption. In this paper we address the issue of securing communication in satellite networks. We describe the different kinds of hybrid network topologies considered for deployment. We discuss various security attacks that are possible in these networks, and survey the different solutions proposed to secure communications in the hybrid networks. We point out important drawbacks in the various proposed solutions, and suggest a hierarchical approach to add security to the hybrid networks.
Service Integration in Next Generation VSAT Networks
(1997) Hadjitheodosiou, Michael H.; ISR; CSHCN
Very Small Aperture Terminal (VSAT) satellite networks have so far been successful in the provision of specific communication services to geographically dispersed users. However, user demands are becoming more complex, and VSAT networks are expected to provide a much wider range of services (voice, data and multimedia). We investigate how this service integration could be achieved and show that performance improvements are possible if efficient multi-access protocols and speech compression with voice activity detection techniques are used. We also discuss the future role VSATs could play in the provision of access to the Integrated Broadband Communications Network to remote users. We discuss the possibility of using VSATs for ATM service provision. The need for careful consideration of the advantages and limitations of using VSAT networks for this type of service is discussed. Finally, we highlight a method for dynamic bandwidth allocation in a broadband satellite network.
Using Commercial Communication Satellite Constellations for Supporting Traffic from NASA Missions
(2002) Hadjitheodosiou, Michael H.; Nguyen, Alex T.; ISR; CSHCN
NASA is interested in using commercial satellites to provide broadband communications support for the International Space Station and other space missions. We describe a large-scale simulation model that we plan to use for detailed performance studies of critical parameters such as QoS guarantees for specific services, traffic routing schemes, transport protocol support, dynamic bandwidth allocation methods, queuing disciplines, and handoff strategies. In this paper we focus on the unique challenges we face and how we plan to use simulations to investigate:ﶴhe feasibility of using proposed commercial constellations to carry mission telemetry, command and control, and tele-science traffic between ground terminals and near-earth spacecraft.ﶴhe end-to-end performance optimization of such systems.
The research and scientific content in this material has been published in the proceedings from the 18th AIAA International Conference on Satellite Systems & Communications, Oakland, CA, April 2000.
Using Commercial Satellites to Provide Communication Support for Space Missions
(2002) Hadjitheodosiou, Michael H.; Nguyen, Alex T.; ISR; CSHCN
NASA is interested in using commercial satellites to provide broadband communications support for future space missions. In this paper, we describe a large-scale simulation model that we plan to use for detailed performance studies of critical parameters. We focus on the unique challenges we face and how we plan to use simulations to investigate:
ﶴhe feasibility of using proposed commercial constellations to carry various classes of traffic between ground terminals and near-earth spacecraft.
ﶴhe performance optimization of such systems.
The research and scientific content in this material has been published inthe proceedings from the GLOBECOM2000 Symposium on Satellite Communications for the New Millennium, San Francisco, Nov, 2000.

Browsing by Author "Hadjitheodosiou, Michael H."

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