Godred Fairhurst

Reliable multicast via satellite: a comparison survey and taxonomy

IP multicasting is an important service, which will be provided by the next generation Internet. A range of applications has emerged which take the advantage of multicast delivery. However, several factors currently hinder large-scale deployment of terrestrial multicast services. It is particularly difficult to support delivery to large groups of users. n n n nSatellites offer a natural way to extend the multicast service to reach this large number of users. They may offer high capacity (especially when using next generation satellite systems) and also eliminate the need for a large number of intermediate routing hops. There are important differences in the way multicast applications operate over satellite. This paper therefore reviews the key design paradigm and offers a critical comparison between different reliable multicast protocol techniques based on a taxonomy. The suitability of a set of the most common reliable multicast protocols is assessed within a satellite environment and conclusions are presented. Copyright

Reinforcement of TCP error recovery for wireless communication

When a wireless link forms a part of a network, the rate of packet loss due to link noise may be considerably higher than observed in a modern terrestrial network. This paper studies TCP performance over a range of link environments and highlights the advantage of recent modifications to TCP (e.g. SACK, New-Reno) for wireless communications. It also identifies two key issues which impact the performance of TCP over error prone links: TCPs reliance on timers to recover from a failed retransmission cycle, and TCPs inability to separate congestion packet loss from other types of packet loss. A solution to the first issue is identified and analysed by simulation, and the factors affecting the second issue are outlined.

‘Digital by Default’ and the ‘hard to reach’: Exploring solutions to digital exclusion in remote rural areas

In the UK, the geography of Information and Communication Technology (ICT) infrastructure required for Internet connectivity is such that high speed broadband and mobile phone networks are generally less available in rural areas compared with urban areas or, in other words, as remoteness and population sparsity increase so too does the likelihood of an area having no or very poor broadband connectivity. Against a policy backdrop of UK Government efforts to bring forward network infrastructure upgrades and to improve the accessibility of broadband services in locations where there is a weak commercial investment case, this paper considers the options for the ‘final few’ in the prevailing ‘Digital by Default’ public services context. The paper outlines the Rural Public Access WiFi Services project, a study focused upon enabling Internet connectivity for commercially ‘hard to reach’ rural areas in the UK. The Rural Public Access WiFi Services concept and the experiment are introduced before findings from a pilot deployment of a broadband service to households in a remote rural area, who may be classified as ‘digitally excluded’, are presented. The paper then reflects on our field experiment and the potential of the Rural Public Access WiFi Services service model as a solution to overcoming some of the digital participation barriers manifest in the urban–rural divide. Early indications show that the Rural Public Access WiFi Services model has the potential to encourage participation in the Digital Economy and could aid the UK Government’s Digital by Default agenda, although adoption of the model is not without its challenges.

Enhancing TCP to support rate-limited traffic

This paper introduces a new TCP congestion control mechanism for rate-limited applications that transmit data in bursts and do not fully utilise their allowed transmission rate. We propose new-CWV, a method that allows a TCP connection to restart quickly from either an idle or application-limited period. Simulation results show that this provides faster convergence to the rate requested by a rate-limited application, demonstrated by a higher throughput, and better utilisation of unused capacity compared to Standard TCP or TCP with Congestion Window Validation.

Towards a flexible Internet transport layer architecture

There is a growing concern that the Internet transport layer has become less adaptive to the requirements of new applications, and that further evolution has become very difficult. This is because a fundamental assumption no longer holds: it can no longer be assumed that the transport layer is only in the scope of end-hosts. The success of TCP and UDP and the ubiquity of middleboxes have led to ossification of both the network infrastructure and the API presented to applications. This has led to the development of workarounds and point solutions that fail to cover many facets of the problem. To address this issue, this paper identifies requirements for a new transport layer and then proposes a conceptual architecture that we argue is both flexible and evolvable. This new architecture requires that applications interface to the transport at a higher abstraction level, where an application can express communication preferences via a new richer API. Protocol machinery can use this information to decide which of the available transport protocols is used. By placing the protocol machinery in the transport layer, the new architecture can allow for new protocols to be deployed and enable evolution of the transport layer.

Integration of TESLA and FLUTE over satellite networks

Researches on multicast has explored security challenges faced by group communications. Multicast transport protocols and multicast security protocols need to work closely to provide reliable and secure multicast services. However, there has been comparatively little work carried out to specify how exactly the two technologies can work together efficiently. In this paper, authors present an example of partially integrating the Timed Efficient Stream Loss-Tolerant Authentication (TESLA) protocol and the File Delivery over Unidirectional Transport (FLUTE) protocol. TESLA provides source authorization and data integrity for multicast groups while FLUTE ensures reliability of the multicast transmission. This paper proposes a loose synchronization mechanism for a unidirectional transmission environment, suited to satellite networks. The proposed algorithm was implemented on a testbed with multicast tunnel between University of Surrey and University of Aberdeen and the results are presented in this paper.

Autonomous monitoring of critical infrastructures

Availability of low-cost imaging devices for embedded applications has enabled wireless multimedia sensor networks that can process and transmit image and video data in addition to scalar data. Such networks can be effectively employed to autonomously monitor: (i) the surface conditions and structural health of bridges and transport infrastructures at various geographical locations; (ii) the operational and environmental conditions of water wells and other life-critical resources in isolated areas. This paper describes an autonomous monitoring system. The paper focus is on critical transport infrastructure and natural resources in remote locations. The system identifies and reports the onset of anomalous conditions enabling infrastructure managers, government and community organizations to reduce service disruption, reduce risks and potentially save lives. This is beneficial to infrastructure owners, users and the local community. Initial system trials on infrastructure monitoring are presented, with further discussion of natural resources monitoring and disaster response in developing countries around the world. These provide a case-study for wider stakeholder involvement from government and public sector organizations, and NGOs.

The SATSIX architecture for next-generation satellite systems with IPv6 and DVB

Broadband satellite will play an important role to provide universal broadband access for the users. In order to lower the cost, the next-generation satellite systems should support IPv6 and seamlessly integrate with terrestrial networks, including wireless local loops. In this paper, a novel network architecture has been proposed as a potential solution to the above problem. Based on the proposed overall network and functional architecture, we have emphasised and presented different aspects of the advanced IPv6-enable networking techniques, such as QoS, multicast, security and mobility. The transport protocols can be used in this network architecture are also studied.

Exploring DSCP modification pathologies in the Internet

Abstract The differentiated service architecture (DiffServ) provides a means for network devices to classify traffic based on the DiffServ codepoint (DSCP) and to map the traffic to a specific QoS forwarding treatment. Successful use beyond the local network depends on consistent remarking and forwarding of the DSCP value inside and at the boundaries of DiffServ domains. This paper provides the results of a new widescale measurement campaign to examine how the DSCP value is altered as packets travel along a set of Internet paths. This allows us to infer whether a packet is likely to receive an appropriate QoS treatment and to comment the opportunities for more widely deploying DiffServ QoS. Our results identify a set of remarking pathologies, revealing that many deployed routers continue to use the previous semantics of the deprecated Type of Service (ToS) field. We also note that is not common to observe clearing of the bits in the DiffServ field, as previously believed for routers in the core of the Internet, although this varies significantly depending on the type of network studied. Our results are related to recent IETF work that recommends use of specific DSCP values.

Analysis of IPv6 encapsulation over ULE and MPE using a regenerative satellite payload

Current DVB-RCS systems present an IPv4-interface and no commercial RCS systems have yet offered IPv6 support. This paper explores encapsulation issues for next generation DVB-RCS terminals that will support IPv6. It assess two alternatives: the Unidirectional Lightweight Encapsulation (ULE) and the Generic Stream Encapsulation (GSE). These are shown to improve efficiency and performance and have been evaluated within a regenerative satellite platform test bed.