Sze-Yao Ni

The broadcast storm problem in a mobile ad hoc network

Broadcasting is a common operation in a network to resolve many issues. In a mobile ad hoc network (MANET) in particular, due to host mobility, such operations are expected to be executed more frequently (such as finding a route to a particular host, paging a particular host, and sending an alarm signal). Because radio signals are likely to overlap with others in a geographical area, a straightforward broadcasting by flooding is usually very costly and will result in serious redundancy, contention, and collision, to which we call the broadcast storm problem. In this paper, we identify this problem by showing how serious it is through analyses and simulations. We propose several schemes to reduce redundant rebroadcasts and differentiate timing of rebroadcasts to alleviate this problem. Simulation results are presented, which show different levels of improvement over the basic flooding approach.

Adaptive approaches to relieving broadcast storms in a wireless multihop mobile ad hoc network

In a multihop mobile ad hoc network, broadcasting is an elementary operation to support many applications. In (Ni et al., 1999), it is shown that naively broadcasting by flooding may cause serious redundancy, contention, and collision in the network, which we refer to as the broadcast storm problem. Several threshold-based schemes are shown to perform better than flooding in (Ni et al., 1999). However, how to choose thresholds also poses a dilemma between reachability and efficiency under different host densities. We propose several adaptive schemes, which can dynamically adjust thresholds based on local connectivity information. Simulation results show that these adaptive schemes can offer better reachability as well as efficiency as compared to the results in (Ni et al., 1999).

Route Maintenance in a Wireless Mobile Ad Hoc Network

A mobile ad-hoc network (MANET) is formed by a cluster of mobile hosts, without the infrastructure of base stations. To deal with the dynamic changing topology of a MANET, many routing protocols have been proposed. In this paper, we consider the route maintenance problem, which includes two parts: route deterioration and route breakage. In a MANET, a route may suddenly become broken because only one host roams away. Even if a route remains connected, it may become worse due to host mobility or a better route newly being formed in the system. Existing protocols, however, will stick with a fixed route once it is discovered, until it is expired or broken. In this paper, we show how to enhance several existing protocols with route optimization and local route recovery capability. So the routing paths can be adjusted on-the-fly while they are still being used for delivering packets and can be patched in minimum wireless bandwidth and delay while route errors occur.

Route maintenance in a wireless mobile ad hoc network

A mobile ad-hoc network (MANET) is formed by a cluster of mobile hosts, each installed with a wireless transceiver, without the assistance of base stations. Due to the transmission range constraint of transceivers, two mobile hosts can communicate with each other either directly, if they are close enough, or indirectly, by having other mobile hosts relay their packets. Several routing protocols, such as DSR, SSA, AODV, and ZRP, have been proposed for a MANET with a dynamically changing topology. In a MANET, a route may suddenly become broken because only one host roams away. Even if a route remains connected, it may become worse due to host mobility or a better route newly being formed in the system. Existing protocols, however, will stick with a fixed route between a source-destination pair once it is discovered, until it expires or is broken. In this paper, we show how to enhance several existing protocols with route optimization and local route recovery capability, such that the routing paths can be adjusted on-the-fly while they are still being used for delivering packets or can be patched in minimum wireless bandwidth and packet transmitting delay while route errors occur.

Toward optimal complete exchange on wormhole-routed tori

In this paper, we propose new routing schemes to perform all-to-all personalized communication (or known as complete exchange) in wormhole-routed, one-port tori. On tori of equal size along each dimension, our algorithms use both asymptotically optimal startup and transmission time. The results are characterized by several interesting features: (1) the use of gather-scatter tree to achieve optimality in startup time, (2) enforcement of shortest paths in routing messages to achieve optimality in transmission time, (3) application of network-partitioning techniques to reduce the constant associated with the transmission time, and (4) the dimension-by-dimension and gather-scatter-tree approach to make possible applying the results to nonsquare, any-size tori. In the literature, some algorithms are optimal in only one of startup and transmission costs, while some, although asymptotically optimal in both costs, will incur much larger constants associated with the costs. Numerical analysis and experiment both show that significant improvement can be obtained by our scheme on total communication latency over existing results.

Circuit-Switched Broadcast in Multi-Port 2D Tori

This paper studies the one-to-all broadcast in a circuit-switched 2D torus of any size with α-port capability. This is a generalization of the one-port and all-port models. Existing results, as compared to ours, can only solve very restricted sizes of tori, and use more numbers of steps.

Circuit-Switched Broadcasting in Multi-Port Multi-Dimensional Torus Networks

The one-to-all broadcast is the most primary collective communication pattern in a multicomputer network. This paper studies this problem in a circuit-switched torus with α-port capability, where a node can simultaneously send and receive α messages at one time. This is a generalization of the one-port and all-port models. We show how to efficiently perform broadcast in tori of any dimension, any size, square or nonsquare, using near optimal numbers of steps. The main techniques used are: (i) a “span-by-dimension” approach, which makes our solution scalable to torus dimensions, and (ii) a “squeeze-then-expand” approach, which makes possible solving the difficult cases where tori are non-square. Existing results, as compared to ours, can only solve very restricted sizes or dimensions of tori, or use more numbers of steps.