Haitham S. Cruickshank

Delay- and Disruption-Tolerant Networking (DTN): An Alternative Solution for Future Satellite Networking Applications

Satellite communications are characterized by long delays, packet losses, and sometimes intermittent connectivity and link disruptions. The TCP/IP stack is ineffective against these impairments and even dedicated solutions, such as performance enhancing proxies (PEPs), can hardly tackle the most challenging environments, and create compatibility issues with current security protocols. An alternative solution arises from the delay- and disruption-tolerant networking (DTN) architecture, which specifies an overlay protocol, called bundle protocol (BP), on top of either transport protocols (TCP, UDP, etc.), or of lower layer protocols (Bluetooth, Ethernet, etc.). The DTN architecture provides long-term information storage on intermediate nodes, suitable for coping with disrupted links, long delays, and intermittent connectivity. By dividing the end-to-end path into multiple DTN hops, in a way that actually extends the TCP-splitting concept exploited in most PEPs, DTN allows the use of specialized protocols on the satellite (or space) links. This paper discusses the prospects for use of DTN in future satellite networks. We present a broad DTN overview, to make the reader familiar with the characteristics that differentiate DTN from ordinary TCP/IP networking, compare the DTN and PEP architectures and stacks, as a preliminary step for the subsequent DTN performance assessment carried out in practical LEO/GEO satellite scenarios. DTN security is studied next, examining the advantages over present satellite architectures, the threats faced in satellite scenarios, and also open issues. Finally, the relation between DTN and quality of service (QoS) is investigated, by focusing on QoS architectures and QoS tools and by discussing the state of the art of DTN research activity in modeling, routing, and congestion control.

Dynamic Balanced Key Tree Management for Secure Multicast Communications

A secure multicast communication is important for applications such as pay-per-view and secure videoconferencing. A key tree approach has been proposed by other authors to distribute the multicast group key in such a way that the rekeying cost scales with the logarithm of the group size for a join or depart request. The efficiency of this key tree approach critically depends on whether the key tree remains balanced over time as members join or depart. In this paper, we present two merging algorithms suitable for batch join requests. To additionally handle batch depart requests, we extend these two algorithms to a batch balanced algorithm. Simulation results show that our three algorithms not only maintain a balanced key tree, but their rekeying costs are lower compared with those of existing algorithms

Dynamics of key management in secure satellite multicast

Security is an important concern in todays information age and particularly so in satellite systems, where eavesdropping can be easily performed. This paper addresses efficient key management for encrypted multicast traffic transmitted via satellite. We consider the topic of encrypting traffic in large multicast groups, where the group size and dynamics have a significant impact on the network load. We consider life cycle key management costs of a multicast connection, and show for a logical key hierarchy (LKH) how member preregistration and periodic admission reduces the initialization cost, and how the optimum outdegree of a hierarchical tree varies with the expected member volatility and rekey factor. This improves network utilization, but encryption at the network layer can pose problems on satellite links. We, therefore, propose and analyze an interworking solution between multilayer Internet protocol security (IPSEC) and LKH that also reduces key management traffic while enabling interworking with performance enhancing modules used on satellite links.

Geographic-Based Spray-and-Relay (GSaR): An Efficient Routing Scheme for DTNs

In this paper, we design and evaluate the proposed geographic-based spray-and-relay (GSaR) routing scheme in delay/disruption-tolerant networks. To the best of our knowledge, GSaR is the first spray-based geographic routing scheme using historical geographic information for making a routing decision. Here, the term spray means that only a limited number of message copies are allowed for replication in the network. By estimating a movement range of destination via the historical geographic information, GSaR expedites the message being sprayed toward this range, meanwhile prevents that away from and postpones that out of this range. As such, the combination of them intends to fast and efficiently spray the limited number of message copies toward this range and effectively spray them within range, to reduce the delivery delay and increase the delivery ratio. Furthermore, GSaR exploits delegation forwarding to enhance the reliability of the routing decision and handle the local maximum problem, which is considered to be the challenges for applying the geographic routing scheme in sparse networks. We evaluate GSaR under three city scenarios abstracted from real world, with other routing schemes for comparison. Results show that GSaR is reliable for delivering messages before the expiration deadline and efficient for achieving low routing overhead ratio. Further observation indicates that GSaR is also efficient in terms of a low and fair energy consumption over the nodes in the network.

The security challenges for mobile ubiquitous services

It is envisaged that in future mobile ubiquitous environments, users will be able to seamlessly, search, access and consume a rich offering of services and content from an array of Service/Content Providers, whilst they are on the move, anytime, anywhere. Unfortunately, this new computing paradigm also brings along new and unique security challenges. Novel security solutions are therefore required. But, in order for appropriate security solutions to be devised, all possible security threats must first be thoroughly analysed, and the corresponding security requirements be identified. In this paper, we examine the security issues germane to a mobile ubiquitous environment. We then suggest some possible solutions which may be employed to address these security issues. Open research issues are also highlighted.

Internet QoS and traffic modelling

Telecommunications networks have migrated from circuit based telephony services to packet based broadband network services. Merging with computer networks, they are being integrated with non-real-time data services on classical Internet integrated multimedia services, including real time voice, video and services on the new generation Internet. Thus, the concepts and requirements of quality of service (QoS) and traffic modelling have also been changed significantly. However, real time services such as voice and video are inelastic, as the transmission bandwidth, transmission time and QoS requirements need to be kept within strict limits and hence are not flexible. On the other hand, elastic services such as file transfer and Web surf are much relaxed with QoS and network resource requirements. Networks need to meet the requirements of both types of services by providing different classes of network services, including best effort service at one end of the spectrum, guaranteed service on the other end, and some others in between, with controlled traffic load. Traffic modelling is one of the important aspects to be considered to meet QoS requirements of services and efficient utilisation of network resources. The paper discusses important QoS issues, techniques for measurement and analysing Internet traffic, and new trends and methodology for Internet traffic modelling. It also presents the results based on the measured Internet traffic to validate the new model and the potential of the model to capture the characteristics of traffic for the Internet.

Networking issues in IP multicast over satellite

This paper describes the issues that arise when using satellites for IP multicast, with the emphasis on multicast protocols and how their implementation depends on the satellite communications platform. Various link layer standards such as DVB-S, DVB-RCS and ATM can be used in satellites with onboard processing, and applied to meet user and network requirements for IP multicast. The paper provides an overview of the networking issues and their interactions. Specifically, we show how multicast networking protocols have to be modified to take into account the satellite link characteristics: these protocols include IGMP, multicast routing protocols and reliable multicast protocols. We also discuss how security systems support IP multicast.

A Reliable and Efficient Encounter-Based Routing Framework for Delay/Disruption Tolerant Networks

This paper addresses delay/disruption tolerant networking routing under a highly dynamic scenario, envisioned for communication in vehicular sensor networks (VSNs) suffering from intermittent connection. Here, we focus on the design of a high-level routing framework, rather than the dedicated encounter prediction. Based on an analyzed utility metric to predict nodal encounter, our proposed routing framework considers the following three cases. First, messages are efficiently replicated to a better qualified candidate node, based on the analyzed utility metric related to destination. Second, messages are conditionally replicated if the node with a better utility metric has not been met. Third, messages are probabilistically replicated if the information in relation to destination is unavailable in the worst case. With this framework in mind, we propose two routing schemes covering two major technique branches in literature, namely: 1) encounter-based replication routing and 2) encounter-based spraying routing. Results under the scenario applicable to VSNs show that, in addition to achieving high delivery ratio for reliability, our schemes are more efficient in terms of a lower overhead ratio. Our core investigation indicates that apart from what information to use for encounter prediction, how to deliver messages based on the given utility metric is also important.

Security analysis for Delay/Disruption Tolerant satellite and sensor networks

In the last few years, Delay/Disruption Tolerant Networking has grown to a healthy research topic because of its suitability for challenged environments characterized by heterogeneity, long delay paths and unpredictable link disruptions. This paper presents a DTN security architecture that focuses on the requirements for lightweight key management; lightweight AAA-like architecture for authentication/authorisation; resilience to Denial of Service attacks and user anonymity.

Evaluation of TCP and Internet traffic via low Earth orbit satellites

The prospect of the Internet as the fastest growing satellite communication application coupled with satellite-based multimedia networks has generated a high level of interest in the performance of TCP over satellite systems. This article presents the network architecture for supporting services based on TCP/IP over satellite. It discusses the key factors that influence TCP performance over satellite links, and compares the benefits and disadvantages of low Earth orbit and geostationary Earth orbit satellite. The article also discusses the feasibility of using LEO satellites to support and expand the Internet. It presents studies of the TCP behavior over a GEO satellite system and LEO satellite constellation based on computer simulations, where two typical Internet applications are taken into consideration: FTP file transfer and Web browsing. The results show that TCP performs much better over the LEO satellite constellation than over the GEO system; even the standard TCP over LEO is better than enhanced TCP over GEO.