Networks Group Seminars - abstracts

Oliver Shepherd

In this presentation, we investigate the behaviour of 802.11 with an analytical model and simulation with the aim of optimising voice Quality of Experience (QoE). The study highlights the 802.11 protocol and our Medium Access Control (MAC) layer analytical model to calculate MAC Service Time. The model is then augmented to include the impacts of buffering traffic under saturated and non-saturated conditions of the network to derive delay, loss and jitter. With the introduction of a QoE framework, we find the acceptable call carrying capacity of a given network. Using the model and simulation, we optimise the carrying capacity of voice calls by adjusting the packetisation period and hence packet size, while keeping an equivalent mean load. Finally, we show the impacts when additional network delay is present.

Matthew Bocci

Carriers around the world are exploiting IP-based technologies to transform their network infrastructure to optimise if for IP and Ethernet based fixed and mobile services. A major part of this is how to deal with the vast array of legacy networks, such as ATM, TDM and Frame Relay, and converge them over a common IP-based infrastructure. Pseudowires and MPLS are key solutions to this, but they would not have been so successful if they had not been developed through the open Internet standards process. This presentation will talk about how the Internet Engineering Task Force has come to dominate the development of new IP-based technologies, and explain how one example of a technology standardised through the IETF (pseudowires) is being used to transform carrier networks.

Ioannis Barakos

In the home, consumer electronic devices become more powerful and networked in order to provide a more ubiquitous computing operation. As devices turn to be more complex, their operation and functionalities become more complicated. Even a simple activity in a house environment requires multiple buttons to be pressed on multiple remote controls.

To address the above problems and to offer a more ubiquitous computing operation in smart home devices, a collaborative context-aware home service management system is designed and examined in this PhD Project. This system has two main roles. The first is to understand the context where a user activity takes place and the second is to orchestrate the available devices in order to undertake this activity. Context-aware functionality requires a number of various sensors to sense the physical environment and the user context (user position, user gestures). For device orchestration, middleware technologies such as the OSGi framework will be extended with service planning capabilities to allow device integration and orchestration.
Finally, some experiments on context acquisition using the SUNSpot (SUN Small Programmable Object Technology) sensor platform, and service and device orchestration management using the JBOSS Drools rule engine will be presented.

Dudley Stark

The coupling method is commonly used in modern probability theory to give a bound on how quickly a Markov chain converges to its stationary distribution. After describing the coupling method for discrete time Markov chains, we will show how it can be applied to the M/M/1 queue.(back)

Peng Jiang

Increasing popularity and higher data requirements of new types of service result in higher demand in wireless networks. Relay based cellular networks have been seen as an effective way to meet the users’ increased bit rate requirements while still retaining the benefits of a cellular structure. The objective of this work is to improve the capacity, performance and scalability of relay based cellular networks by using the physical layer to mitigate problems of load balancing and to increase the flexibility of coverage so that coverage is provided at the right place at the right time. The work is divided into four aspects: Base station control option investigates the potential capability of existing antenna systems, such as sector antenna or omni-directional antenna. Self-organizing relay station is investigated for the fast deployment in the relay station control option. Radio resource allocation and flexible radio coverage prediction are investigated for farther optimization. A Mobile WiMAX simulator has been developed to allow evaluations of the proposed network architectures.(back)

Luo Liu

A mobile ad hoc network (MANET) is a collection of mobile nodes that can communicate with each other without using any fixed infrastructure. It is necessary for MANETs to have efficient routing protocol and quality of service (QoS) mechanism to support multimedia applications such as video and voice. Node-Disjoint Multipath Routing Protocol (NDMR) is a practical protocol in MANETs: it reduces routing overhead dramatically and achieves multiple node-disjoint routing paths. Because QoS support in MANETs is important as best-effort routing is not efficient for supporting multimedia applications, this research presents a novel approach to provide that support. In this research NDMR is enhanced to provide a QoS enabled NDMR that decreases the transmission delay between source and destination nodes. Multi-rate mechanism is also implemented in the new protocol so that the NDMR QoS can minimise the overall delays. It is shown that these approaches lead to significant performance gains. A modification to NDMR is also proposed to overcome some of the limitations of the original.(back)

Guozhi Song

It is widely expected that next-generation wireless communication systems will be heterogeneous, integrating a wide variety of wireless access network. Of particular interest at the moment is a mix of cellular networks (GSM/GPRS and WCDMA) and wireless local area networks (WLANs) to provide complementary features in terms of coverage, capacity and mobility support. If cellular/WLAN interworking is to be the basis for a heterogeneous network then the analysis of complex handover traffic rates in the system (especially vertical handover) is one of the most essential issues to be considered. This talk describes the application of queuing-network theory in the modelling of this heterogeneous wireless overlay system. A network of queues (or queuing network) is a powerful mathematical tool in the performance evaluation of many complex systems. It has been used in the modelling of hierarchically structured cellular wireless networks with much success, including queuing network modelling in the study of cellular/WLAN interworking systems. In the process of queuing network modelling, obtaining the network topology of a system is usually the first step in the construction of a good model, but this topology analysis has never before been used in the handover traffic study in heterogeneous overlay wireless networks. In this report, a new topology scheme to facilitate the analysis of handover traffic is proposed. The structural similarity between hierarchical cellular structure and heterogeneous wireless overlay networks is also compared. By replacing the microcells with WLANs in a hierarchical structure, the interworking system is modelled as an open network of Erlang loss systems and with the new topology, the performance measures of blocking probabilities and dropping probabilities can be determined. Both single type and multi type of traffic have been considered. Example scenarios have been used to validate the model, the numerical results showing clear agreement with the realistic situation.(back)

Michael J Neve

Recent advances in indoor wireless LAN technologies have realised the dream of untethered and low-cost broadband access to internet services. However, the success (or otherwise) of these systems is very dependent on the decisions made at the time of their deployment. Reliable techniques for predicting both coverage and levels of interference are required. Most existing techniques/models are empirically-based and do not therefore give insight into the physical nature of the propagation process. Models which possess a deterministic basis are advantageous in this regard, but are frequently too complex to use in day-to-day applications.
In this presentation, a programme of research into propagation modelling using computational electromagnetic techniques (specifically the FDTD) being undertaken at The University of Auckland will be discussed. Radio wave propagation in the presence of a steel-reinforced concrete corner will be considered initially, followed by a discussion of how electromagnetic energy propagates between floors in a building. The insight gained from these analyses is being used to formulate simplified mechanistic models for use in system planning applications. (back)

John Pollard:

A complete wireless sensor network is described, with an emphasis on medical applications. All hardware and software components have been designed and built in prototype form. A security system ensures privacy of information. Patients, carers, nurses, doctors and administrators may communicate readily over the World-Wide Web. The final communication links are wireless to allow mobility of the actors.
A network of Bluetooth-enabled sensor devices with a Backbone scaleable communication network using routers is proposed. A topology that allows redundancy in communications has been shown by simulation to offer more than two orders-of-magnitude improvement in real-time packet data reliability. This is important for medical and other systems where sensor alarms and real-time data must be reliable.Example applications of sensors suitable for networks are: Voice over Internet Protocol, mobile cameras, safe pill-dispensing using RFID tags, position determination, inventory and access control. (back)

Zhijia Huang:

Complex networks such as the Internet, power transmission lines and telephone systems are susceptible to catastrophic failures in which the whole network ceases to function. An avalanche-like breakdown is the most common cause of a catastrophe. Failure of a single node, that is sensitive to overloading, would induce load redistribution among the network. This redistribution of load will overload other nodes, triggering an avalanche of failures. As a result, the entire network fragments into disconnected sub-networks. We are interested to know if a catastrophic-network has a distinctive topology and if the cause of the cascading behaviour scales with the size of the network. To be able to address these questions we need to construct catastrophic networks in a controlled and efficient way. (back)

Ben Parker:

This work looks at combining statistics with areas of electronic engineering to see if we can use statistical concepts to better understand data networks. In particular, we present some applications of how we can use statistical methodology for gathering "the best" information on unknown network parameters such as packet loss probability, bandwidth, and packet delay. We examine how, by considering the network state as a Markov Chain, an approximate model of a network can be used to find an optimal probing rate. We also show how we can use an exact simulation of a network to balance the competing needs to gather accurate readings, but also to obtain them quickly. (back)

Celia Glass:

The main focus of the talk will be the optimisation of Routing and Wavelength Assignment (RWA) of a pure-optical network. I will use this, and other, examples to illustrate what Mathematics have to offer Engineers, and what challenges telecommunications engineering has to offer Mathematicians.
When wavelength conversion is present, the RWA problem may be solved to optimality using Integer Linear Programme (ILP). However, the general problem is more challenging. Without wavelength converters the problem has a completely different mathematical structure. An additional step involving graph colouring is generally recommended, to establish wavelength assignment for the specified routing. There is some confusion in the literature about the wavelength capacity on individual links guaranteed by the ILP solution and that achievable in practice. I will explain why there is an optimality gap (when more wavelengths are required than are incident on any one link), and identify circumstances under which it might arise. Various matrices and graphs provide a deeper unde\standing of the structure of the network. One example involves odd cycles in the demand graph. More generally, I illustrate the optimality gap in terms of an explicit depiction in the form of a so called interference graph. This gives rise to a generalised graph colouring problem encompassing both routing and wavelength assignment, which I offer as a challenge to Mathematicians.
This research with Dr. Chris Phillips has been extended to a novel layered connection management system based on some earlier Nortel Networks industrial research. The basic approach is to employ a dual-level architecture. The control of the lower level by the upper level is carried out via two means, namely influence-based path calculation for short-lived connections and intrusive redeployment for long-lived connections. The results are very promising, as they indicate an improvement in performance of over 20% compared to standard approaches. This level of improvement is common following the use of suitable mathematical optimisation techniques.
This research was carried out while I was seconded to QMUL Electronics Engineering Department under and EPRSC Discipline Hopping grant. The following and other mysteries of inter-disciplinary work should be illuminated in this seminar.

1. How can 30% additional internet provision in a network, actually provide less than 5% slack for traffic?

2. How can an algorithm be considered optimal in the Engineering literature on all standard internet networks, and yet be seriously sub-optimal mathematical, and for future internet traffic?

3. Why do Mathematicians take so long to come up with an answer, instead of ‘just getting on with it’?

4. Where do mathematical challenges arise in other areas of telecommunications?. (back)

Jonathan Pitts:

To satisfy the low delay, low jitter performance requirements of real-time trafﬁc such as VoIP, DiffServ EF class using priority scheduling is normally recommended. This requires limits on admissible load, conﬁgured to meet the most stringent QoS in the real-time trafﬁc mix. To handle multiple real-time service types with heterogeneous QoS, we propose a novel alternative: DiffServ AF classes with RED queue management. Recent queue theoretic advances have demonstrated RED’s ability to control the delay distribution of inelastic trafﬁc under congested conditions. This signiﬁcantly reduces late delivery of packets at the cost of (probabilistically) dropping a greater proportion in the network. We used the ITU-T E-model to express how these performance measures affect voice quality; results demonstrate that our novel AF conﬁguration enables the network to carry more trafﬁc for a given quality level, and to degrade more gracefully under severe congestion. (back)

Yiran Gao:

A new dynamic Virtual Private Network (VPN) architecture based on a new coordinating component called the Dynamic VPN Manager (DVM). The DVM manages available network resources and allocates these resources to the users’ applications. To achieve this, a resource scheduling algorithm is designed to assign the network resources in the dynamic environments. Simulations are carried to study the proposed algorithm’s performance. The results show that the scheme is feasible and performs well in dynamic network scenarios, where no knowledge of future events exist, compared with static algorithms which are given complete knowledge of all job arrivals. (back)

Weizhi Luo:

Some of the important advantages of having an integrated mobile network environment would be seamless communications, joint resource management and adaptive quality of service. In such environment, operators would not need to reject the user requests, but redirect them to appropriate networks. However, the sought aims of an integrated network system still have many pending issues. One of them is the selection of the most appropriate radio access network (RAN) according to the requested service and the context information about the user and the networks. This seminar addresses this issue by proposing two RAN selection algorithms inside realistic internetworking system architecture. (back)

Liang Zekeng:

Ambient Intelligence (AmI) is a vision for ubiquitous computing in which digital devices are embedded in a physical environment, and exhibit a strong and explicit notion of person awareness, i.e., devices which recognise people, their situational context and be able to adapt and anticipate peoples’ desires. This alleviates humans from having to interact with systems at a detailed and syntactic level. In order for systems to be person aware, it is proposed that they need to be designed to exhibit a notion of social intelligence in terms of autonomy, proactiveness and shared goals. Such a notion of intelligence is a central notion of multi-agent systems. A first step is to design AmI devices to exhibit social intelligence at an individual and local level, e.g., an AmI light controller can detect if it is dark and a person is present and will switch on and remain on while the person is present. However, such a simple model is\limited because the social intelligence is directed at the person. An extension to the ambient intelligence model is needed such that allows it to operate between multiple devices, enabling them to cooperate as a team to support person-awareness, e.g., the social interaction between multiple lights could help to decide which of the lights was redundant and not switch on. This seminar proposes a model of the social intelligence that allows devices to operate between them. An attempt is given to validate the model by comparing the test results of the three simple simulators (manual control, semi-auto control and self-managing). (back)