Teck Meng Lim

Distributed Neighbor Discovery in Ad Hoc Networks Using Directional Antennas

In this paper, we propose a distributed neighbor discovery algorithm in ad hoc networks using directional antennas. A newly joining node obtains the information about its neighbors in both its omnidirectional and directional range by querying a subset of its omnidirectional neighbors. The main contribution of the proposed algorithm is that it does not require all neighbor nodes to be involved in the discovery process. Simulation results show that the algorithm performance closely tracks the theoretical analysis and only requires a fraction of the neighbors to be involved in the discovery process.

TMSP: Terminal Mobility Support Protocol

Mobile IP enables IP mobility support for mobile node (MN), but it suffers from triangular routing, packet redirecting, increase in IP header size, and the need for new infrastructure support. This paper details an alternative to enable terminal mobility support for MN. This scheme does not suffer from triangular routing effect and does not require dedicated infrastructure support such as home agent. It also does not increase the size of the IP header and does not require redirection of packets. These benefits are enabled with a tradeoff, which requires modifications on MN and its correspondent node. It uses an innovative IP-to-IP address mapping method to provide IP address transparency for applications and taps on the pervasiveness of SIP as a location service. From our analysis, we show that TMSP is much more efficient than mobile IP in terms of the number of hops as well as overhead. Our prototype implementation also shows that TMSP provides seamless communication for both TCP and UDP connections and the computational overhead for TMSP has minimal impact on packet transmission.

Quantum-Based Earliest Deadline First Scheduling for Multiservices

Latency-rate (LR) schedulers have shown their ability in providing fair and weighted sharing of bandwidth with an upper bound on delivery latency of packets while earliest departure first (EDF) schedulers have shown their ability in providing LR-decoupled service whereby the delivery latency of packets is not bounded by the reserved rate. However, EDF schedulers require traffic shapers to ensure flow protection. We propose quantum-based earliest deadline first scheduling (QEDF), a quantum-based scheduler that provides flow protection, throughput guarantee and delay bound guarantee for flows that require LR-coupled and LR-decoupled types of reservations. It classifies flows into time-critical (TC), jitter-sensitive (JS), and rate-based (RB) classes and uses a quality-of-service forwarding rule to determine the next packet to be serviced by the scheduler. It provides nonpreemptive priority service to TC queues. This allows LR-decoupled reservation for flows that have a low rate and intolerable delay. Packets from JS queues can be delayed by other packets if forwarding the latter will not result in the former missing its deadline. As a quantum-based scheduler, the QEDF scheduler provides throughput guarantees for RB queues. We present both analytical and simulation results of QEDF, whereby we evaluated QEDF in its deployment as a single-class as well as a multiservice scheduler

Unicorn: voluntary computing over Internet

Unicorn provides an architecture using Java to harness the vast processing power on the Internet for distributed computing applications. It employs the code-shipping paradigm to broker this processing power. The client can either make use of the suite of applications provided by Unicorn or upload his own applications to the server together with the data to be processed. These tasks are distributed in parallel to idle hosts logged on to the Unicorn server. A set of Unicorn programming tools, including the Unicorn Application Interface and Broker ServerLite (a scaled-down version of Unicorn Broker Server), is distributed to clients to facilitate applications development. The framework handles all the communication needs of the broker and hosts, leaving the clients to concentrate on the functionality of their applications. In addition, a mechanism for resource pricing has been incorporated to provide incentives for sharing of processing power. The clients are charged and host systems are paid according to the resources used. The broker takes a commission in the transactions.

A Mobility Scheme for Personal and Terminal Mobility

An IP mobility support protocol that enables personal and terminal mobility for IP-based applications is put forward. This protocol does not require new network entities or support from network service providers. It comprises an innovative IP-to-IP address mapping module at the network layer and an user agent to interact with a directory service server and correspondent nodes. It does not require a permanent IP address and a home server. It does not use tunnelling on mobile nodes nor alter route path of IP packets. In this paper, we describe our implementation and present our experimental results. Experiments show that this protocol works for UDP and TCP connections without affecting the throughput of the mobile node on a wireless LAN. Related works are also discussed and quantitatively compared. As an example, this protocol provides seamless execution for applications like VoIP and video conferencing on mobile nodes that roam across wireless networks.

Secure communications between bandwidth brokers

In the Differentiated Services (DiffServ) architecture, each domain has a Bandwidth Broker to provide the resources management, primarily bandwidth reservation. In a multi-domain environment, Simple Inter-domain Bandwidth Broker Signaling (SIBBS) protocol is proposed for the inter-domain communication protocol proposed for bandwidth broker communication. Since the information exchanged between BBs are sensitive in sense of Service Level Agreement (SLA), the communications between the inter-domain bandwidth brokers should be protected from attacks. This paper presents the incorporation of the Public Key Infrastructure (PKI) security model for SIBBS. A prototype system with the security elements as well as the implementation of the SIBBS was successfully developed and tested.

Terminal-Assisted Network Mobility Management

In network mobility support for wireless ad hoc networks, mobile routers (MRs) are connected to access router (AR) by ad hoc routing. Mobile network nodes (MNNs) connect to an MR to communicate to distant correspondent nodes (CNs). Previous works on network mobility in mobile IPv6 involve packet redirection through a home agent; this redirection is costly in both bandwidth and delay. In this paper, we propose a terminal-assisted network mobility management scheme, which requires neither permanent nodes IP address nor additional network servers/infrastructure support. With this scheme, IP packets redirection is not necessary; IP packets are routed directly between MNNs and CNs. Our scheme is implemented in three components: an IP-to-IP address mapping scheme on the MNN, an IPv6 header extension on each IP packet, and an IP address redirection scheme on the MRs. An MNN is located by a uniform resource identifier (URI) provided by a directory service that maps URI to IP address. Through numerical analysis, we show that our mobility management scheme exhibits better efficiency compared with that of mobile IPv6.

Effectiveness of Explicit Stations Grouping in Crowded Wireless LANs

In this letter, we evaluate the effectiveness of a multi-stage contention scheme for wireless local area networks (WLANs) medium access control (MAC). Multi-stage contention schemes basically divide the stations into smaller groups to resolve the contention more efficiently. Previous researchers have proposed virtual grouping schemes for WLANs MAC. Here we quantitatively analyze what can be achieved with a simple grouping scheme, i.e. through multi-stage contention. Our analysis shows that the multi-stage scheme is efficient in resolving contention, making it a good alternative to the commonly used exponential backoff mechanism.

Pervasive communication for commuters in public buses

Using inter-vehicular communications as a mobile backbone has been an area of active research in recent years. We propose a pervasive mobile communication network that utilises our BUSNet to provide Internet access for the public transportation system such as buses, taxi and trains. These vehicles act as the wireless backbone which connects to the Internet. Thus, users of cellular network can have a faster and lower cost pervasive mobile communication when they use public transports. Unique to our ad hoc to Internet architecture is a a lightweight Access Router discovery protocol, an event-driven neighbouring access router discovery protocol, and a distributed location service with privacy protection that works in conjunction with Internet protocol mobility. Moreover, we propose two information discovery protocols that use the properties of the movement of buses and access routers to provide information for possible advance services, prediction and quality-of-service.

IPv6 network mobility for flat ad hoc routing protocol

We apply the mobility support of IPv6 to a wireless network where flat ad hoc routing protocol is used for interconnecting mobile routers. The use of flat routing protocol removes the need for more than one level of recursive nesting to form a wireless network backbone. We introduce a redirect header for mobile IPv6, which reduces the overhead of tunnelling by half in wireless network where bandwidth is limited. Through numerical evaluations, we show that this header aids in reducing the tunnelling overhead. We also discuss the current route optimisation proposals and their applicability to our network scenarios