Marc R. Pearlman

On the impact of alternate path routing for load balancing in mobile ad hoc networks

Alternate path routing (APR) can provide load balancing and route failure protection by distributing traffic among a set of diverse paths. These benefits make APR appear to be an ideal candidate for the bandwidth limited and mobile ad-hoc networks. However, we find that APRs potential is not fully realized in ad-hoc networks because of route coupling resulting from the geographic proximity of candidate paths between common endpoints. In multiple channel networks, coupling occurs when paths share common intermediate nodes. The coupling problem is much more serious in single channel networks, where coupling also occurs where one path crosses the radio coverage area of another path, The networks inherent route coupling is further aggravated by the routing protocol, which may provide an incomplete view of current network connectivity. Through analysis and simulation, we demonstrate the impact of route coupling on APRs delay performance in ad-hoc networks. In multiple channel environments, APR is able to provide a 20% reduction in end-to-end delay for bursty data streams. Though these gains are appreciable, they are about half what we would expect from APR with independently operating routes. Route coupling is so severe in single channel networks that APR provides only negligible improvements in quality of service.

Independent zone routing: an adaptive hybrid routing framework for ad hoc wireless networks

To effectively support communication in such a dynamic networking environment as the ad hoc networks, the routing framework has to be adaptable to the spatial and temporal changes in the characteristics of the network, such as traffic and mobility patterns. Multiscoping, as is provided through the concept of the Zone Routing Protocol (ZRP) for example, can serve as a basis for such an adaptive behavior. The Zone Routing framework implements hybrid routing by every network node proactively maintaining routing information about its local neighborhood called the routing zone, while reactively acquiring routes to destinations beyond the routing zone. In this paper, we propose the Independent Zone Routing (IZR) framework, an enhancement of the Zone Routing framework, which allows adaptive and distributed configuration for the optimal size of each nodes routing zone, on the per-node basis. We demonstrate that the performance of IZR is significantly improved by its ability to automatically and dynamically tune the network routing operation, so as to flexibly and robustly support changes in the network characteristics and operational conditions. As a point of reference, through this form of adaptation, we show that the volume of routing control traffic overhead in the network can be reduced by an order of magnitude, under some set of parameter values. Furthermore, the adaptive nature of IZR enhances the scalability of these networks as well.

The performance of a new routing protocol for the reconfigurable wireless networks

In this paper, we investigate the performance of a novel routing protocol, the zone routing protocol (ZRP), that was introduced in Haas (1997). The protocol is targeted at a special class of ad-hoc networks, which we refer to as the reconfigurable wireless networks (RWNs). RWNs are distinguished from other ad-hoc networks by their increased node mobility, larger number of nodes, and wider network span. We demonstrate that ZRP significantly reduces the delay and the amount of routing overhead by providing each node with continuous updates of its local neighborhood (routing zone) topology only. The structure of the routing zone is exploited to efficiently acquire routes on demand for destinations that lie beyond a nodes routing zone. By adjusting a single parameter-the size of the routing zone-the ZRP can adapt to a variety of network operational conditions.

Elective participation in ad hoc networks based on energy consumption

In ad hoc networks, each node utilizes its limited resources to carry out the collective operation of the network. It is not always in the best interests of the networks nodes to demand the continuous participation of all nodes in the network operations. We propose an energy dependent participation (EDP) scheme, where a node periodically re-evaluates its participation in the network based on the residual energy in its battery. More importantly, a node gives special consideration to supporting the communication needs of its active network applications and preventing further network partitioning. EDPs localized partition checking algorithm is particularly well suited for the zone routing protocol, where the link-state information is proactively maintained within each nodes local zone and routes to faraway nodes are reactively obtained via global queries. Through simulations, we evaluate the impact of our proposed scheme on battery life and network connectivity. Our results suggest that the EDP scheme can increase the usable lifetime of a battery-constraint ad hoc network by over 50%.

Alternate path routing in mobile ad hoc networks

This research used a custom event-driven network simulator to evaluate alternate path routings (APRs) behavior in mobile ad hoc networks (MANETs). In particular, it investigated how much route-diversity is inherent in typical ad-hoc networks, and the ability of a globally reactive routing-protocol (such as the zone routing protocol) to capture and utilize that route diversity. It then explored the end-to-end capacity improvements provided by APR. Results indicate that APRs benefit is highly dependent on both the network topology and the channel access methods.

Using multi-hop acknowledgements to discover and reliably communicate over unidirectional links in ad hoc networks

Neighbor discovery protocols are based on the receipt of an acknowledgement in response to a node advertisement. Traditionally, the advertisement and acknowledgement are sent in opposite directions across the same link. As a result, these protocols are only able to discover bidirectional links. The exclusion of unidirectional links can reduce the networks capacity and also lead to network partitioning. These concerns are particularly relevant to ad hoc networks, where bandwidth and transmission power are limited resources and links are not necessarily bidirectional. To support the discovery and subsequent use of unidirectional links, we propose the multi-hop broadcast and unicast relay of link layer acknowledgements. Through simulation of an ad hoc network with reduced transmission power support, we demonstrate that the proposed multi-hop feedback techniques are able to discover nearly all of the unidirectional links, improving network connectivity by 30% and reducing the length of shortest hop paths by 25%.

Hybrid routing: the pursuit of an adaptable and scalable routing framework for ad hoc networks

Advances in ad hoc network research have opened the door to an assortment of promising military and commercial applications for ad hoc networks. However, because each application has unique characteristics (such as traffic behavior, device capabilities, mobility patterns, operating environments, etc.), routing in such a versatile environment is a challenging task, and numerous protocols have been developed to address it. While many protocols excel for certain types of ad hoc networks, it is clear that a single basic protocol cannot perform well over the entire space of ad hoc networks. To conform to any arbitrary ad hoc network, the basic protocols designed for the edges of the ad hoc network design space need to be integrated into a tunable framework.The Zone Routing framework demonstrates how multi-scoping can provide the basis for a hybrid routing protocol framework. Zone Routing proactively maintains routing information for a local neighborhood called the routing zone (local scope), while reactively acquiring routes to destinations beyond the routing zone. In this paper, we review the Zone Routing concept and propose Zone Routing with independently sized routing zones capability. With this capability, each of the nodes in the network can adaptively configure its own optimal zone radius in a distributed fashion. We show that the performance of Zone Routing is significantly improved by the ability to provide fine-tuned adaptation to local and temporal variations in network characteristics.

The performance of query control schemes for the zone routing protocol

In this paper, we study the performance of route query control mechanisms for the Zone Routing Protocol (ZRP) for ad-hoc networks. The ZRP proactively maintains routing information for each node’s local neighborhood (routing zone), while reactively acquiring routes to destinations beyond the routing zone. This hybrid routing approach can perform more efficiently than traditional routing schemes, but only with the proper query control mechanisms. Our proposed query control schemes exploit the structure of the routing zone to provide enhanced detection (Query Detecrion (QDUQD2)), termination (Early Termination (ET), Loopback Termination (LT)) and prevention (Backward Seaich Prevention (BSP), Selective Bordercasting (SBC)) of overlapping queries. These mechanisms allow the ZRP to provide routes to all accessible network nodes, with only a fraction of the control trafftc generated by purely proactive distance vector or purely reactive flooding schemes, and in less than half the time of a route query flood.

Evaluation of the Ad-Hoc connectivity with the zone routing protocols

In this paper, we evaluate the novel routing protocol for a special class of ad-hoc networks, termed by us the Reconfigurable Wireless Networks (RWNs). The main features of the RWNs are: the increased mobility of the network nodes, the large number of nodes, and the large network span. We argue that the current routing protocols do not provide a satisfactory solution for routing in this type of an environment. We propose a scheme, coined the Zone Routing Protocol (ZRP), which dynamically adjusts itself to the operational conditions by sizing a single network parameter - the Zone Radius. More specifically, the ZRP reduces the cost of frequent updates of the constantly changing network topology by limiting the scope of the updates to the immediate neighborhood of the change - the Zone Radius. We study the performance of the scheme, evaluating the average number of control messages required to discover a route within the network. Furthermore, we compare the scheme’s performance, on one hand, with reactive flooding-based schemes, and, on the other hand, with proactive distance-vector schemes.

On the performance of a routing protocol for the reconfigurable wireless network

Reconfigurable wireless networks (RWNs) are a special class of ad-hoc networks that are characterized by: large geographical coverage, wide range of nodal mobility, and large nodal density. Recently, a new routing protocol for this type of networks was proposed and coined the zone routing protocol (ZRP). The main feature of the ZRP protocol is its dynamic behavior-the operation of the scheme is governed by a single parameter, the zone radius, which adjusts the schemes behavior from purely reactive to proactive routing. We study the performance of the scheme, evaluating the average number of control messages required to discover a route within the network. Our results show that by properly seizing the zone radius, the routing overhead can be lower (sometimes much lower) than the overhead of both reactive and proactive schemes.