Associativity-Based Routing for Ad Hoc Mobile Networks

This paper presents a new, simple and bandwidth-efficient distributed routing protocol to support mobile computing in a conference size ad-hoc mobile network environment. Unlike the conventional approaches such as link-state and distance-vector distributed routing algorithms, our protocol does not attempt to consistently maintain routing information in every node. In an ad-hoc mobile network where mobile hosts (MHs) are acting as routers and where routes are made inconsistent by MHs' movement, we employ an associativity-based routing scheme where a route is selected based on nodes having associativity states that imply periods of stability. In this manner, the routes selected are likely to be long-lived and hence there is no need to restart frequently, resulting in higher attainable throughput. Route requests are broadcast on a per need basis. The association property also allows the integration of ad-hoc routing into a BS-oriented Wireless LAN (WLAN) environment, providing the fault tolerance in times of base stations (BSs) failures. To discover shorter routes and to shorten the route recovery time when the association property is violated, the localised-query and quick-abort mechanisms are respectively incorporated into the protocol. To further increase cell capacity and lower transmission power requirements, a dynamic cell size adjustment scheme is introduced. The protocol is free from loops, deadlock and packet duplicates and has scalable memory requirements. Simulation results obtained reveal that shorter and better routes can be discovered during route re-constructions.     

Crossover switch discovery for wireless ATM LANs

The emergence of Wireless Local Area Networks (WLANs) has brought about the possibility of mobile computing. In order to maintain connectivity to Mobile Hosts (MHs), a handover mechanism is needed as MHs migrate from one Base Station's (BS) wireless cell to another. Current handover schemes are mainly catered for connectionless WLANs (example Mobile IP) which do not have the ability to support Quality of Service (QoS) for continuous media traffic. Hence, mobility for connection-oriented WLANs (example Wireless ATM) should be considered. The problem faced in a connection-oriented WLAN is the ability to provide a fast, efficient and continuous handover mechanism. Mechanisms that can meet most of these requirements are the Incremental and Multicast Based Re-establishment handover schemes. In particular, the incremental re-establishment scheme relies on the presence of a Crossover Switch (CX) to establish the new partial circuits to the new BS. In this paper, five CX discovery schemes are proposed to compute and select the optimised new partial path such that both the set-up latency and network resource consumption associated with the handover are small. The proposed CX discovery schemes (Loose Select, Prior Path Knowledge, Prior Path Optimal, Distributed Hunt and Backward Tracking) are suitable for wireless ATM LANs employing either the centralised or distributed connection management approach with either distance-vector or link-state-like minimumhop routing schemes. Simulation results obtained from a trace-driven mobile network simulator on four different network topologies (Random, Star, Tree and Hierarchical Redundancy) reveal that the Prior Path Knowledge and Distributed Hunt discoveries outperform the other schemes in various aspects. Finally, using the IBM PARIS Gigabit Network as an example, we show how CX discovery is incorporated with routing, connection management and QoS.This paper also appears in part at the IEEE INFOCOM'96, San Francisco, California, March 1996 as Performance Evaluation of Crossover Switch Discovery Algorithms For Wireless ATM LANs.C-K Toh is supported by a King's College Cambridge External Research Studentship and a Cambridge Commonwealth Trust Scholarship.     

A hybrid handover protocol for local area wireless ATM networks

While handovers of voice calls in a wide area mobile environment are well understood, handovers of multi-media traffic in a local area mobile environment is still in its early stage of investigation. Unlike the public wireless networks, handovers for multi-media Wireless LANs (WLANs) have special requirements. In this paper, the problems and challenges faced in a multi-media WLAN environment are outlined and a multi-tier wireless cell clustering architecture is introduced. Design issues for multi-media handovers are specified and a fast, continuous and efficient hybrid handover protocol is proposed. The protocol is scalable and supports source and destination mobile handovers in a mutually exclusive manner. Crossover switch (CX) discovery is also introduced to support fast inter-cluster handovers with consideration given to Mobile Quality of Service (M-QoS). The resulting wireless ATM LAN exhibits a distributed mobile location management, call admission control and handover management architecture. A prototype of the proposed handover protocol is implemented into a Cambridge Fairisle ATM switch and the results of handovers for a single Mobile Host (MH) with a single on-going connection are evaluated. It was found that implementing transport mobility for a wireless ATM environment is not practical as the cell re-routing function changes the traffic characteristics and is not scalable to increasing cell rate and to the number of mobile connections. The data-link layer mobility implementation however, is found to work well. The protocol provides symmetric data disruption to traffic flows in both directions and up to seventy-five intra-cluster handovers can be supported in a second. Throughout the experiment, cells arrive in sequence with no cell loss observed during the handover, up to the capacity limit of the ATM switch. Finally, zig-zag handovers and handovers for a single MH with multiple on-going unicast connections are performed in order to evaluate the robustness and performance of the protocol under different MHs' migration and communication environment.Parts of this paper appeared in the ACM First International Conference on Mobile Computing and Networking (MOBICOM'95), Berkeley, California, November 1995 as The Design & Implementation of A Hybrid Handover Protocol For Multi-Media Wireless LANs.C-K Toh is supported by a King's College Cambridge External Research Studentship and a Cambridge Commonwealth Trust Scholarship.     

Satellite ATM network architectures: an overview

A satellite ATM network has been envisioned as the next information super-skyway. There has been a migration from traditional bent pipe satellites to onboard processing ATM satellites. The current congestion in the Internet has motivated the use of alternate paths-using satellites to support global Internet transport and access. This article presents the various system and protocol layer architectures of SATM networks     

A Street Broadcast Reduction Scheme (SBR) to Mitigate the Broadcast Storm Problem in VANETs

In urban vehicular wireless environments, several vehicles can send warning messages and so every vehicle within the transmission range will receive the broadcast transmission, possibly rebroadcasting these messages to other vehicles. This increases the number of vehicles receiving the traffic warning messages. Hence, redundancy, contention, and packet collisions due to simultaneous forwarding (usually known as the broadcast storm problem), can occur. In the past, several approaches have been proposed to solve the broadcast storm problem in wireless networks such as Mobile ad hoc Networks MANETs. In this paper, we present Street Broadcast Reduction SBR, a novel scheme that mitigates the broadcast storm problem in VANETs. SBR also reduces the warning message notification time and increases the number of vehicles that are informed about the alert.