DiffServ offers an attractive solution to quality of service (QoS) for mobile ad-hoc networks (MANET)s since the overhead of alternative flow based QoS metrics and signaling is not required. However, within prioritized classes and in the presence of dynamically forming bottlenecks, DiffServ can lead to brittle failure modes in which all flows are highly penalized and subsequently fail rather than maintaining some flows at required QoS levels for latency or packet loss. This problem is particularly difficult for UDP traffic, which does not respond to random early detection (RED) like throttling mechanisms in the presence of congestion. This paper proposes an augmentation of DiffServ QoS over MANET that utilizes metrics available through routing protocols to prevent, and resolve congestion. This is done in a manner that promotes maintenance of some high priority UDP (for example voice over IP) flows in the presence of bottlenecks. The biased early drop (BED) algorithm is introduced to maintain high continuity of UDP flows in the presence of congestion within the same class of service.

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 node's 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.

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 network's 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. EDP's localized partition checking algorithm is particularly well suited for the zone routing protocol, where the link-state information is proactively maintained within each node's 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%.

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 a local neighborhood (routing zone), while reactively acquiring routes to destinations beyond the routing zone. This hybrid routing approach can be more efficient than traditional routing schemes. However, without proper query control techniques, the ZRP cannot provide the expected reduction in the control traffic. Our proposed query control schemes exploit the structure of the routing zone to provide enhanced detection and prevention of overlapping queries. These techniques can be applied to single- or multiple-channel ad hoc networks to improve both the delay and control traffic performance of ZRP. Our query control mechanisms allow ZRP to provide routes to all accessible network nodes, with less control traffic than purely proactive link state or purely reactive route discovery, and with less delay than conventional flood searching.

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 APR's 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 network's 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 APR's 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.

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 network's 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%.

Previous work in ad hoc network routing protocol development has demonstrated how global route discovery can be performed more efficiently by leveraging the known topology of each node's local surrounding area (routing zone). In this paper, we demonstrate how routing zones can also be applied to the maintenance of these discovered routes. In particular, knowledge of routing zone connectivity can be used to automatically bypass link failures and provide "shortcuts" across sub-optimal segments of the route. These mechanisms contribute to a reduction in network load and end-to-end delay, while improving the stability of active connections.

In this paper, we investigate the diversity properties of routes acquired through traditional route query floods. The on-demand nature of query-based (reactive) routing is appropriate for networks with dynamic network topologies (such as ad-hoc networks). An intrinsic feature of route query protocols is the support for multiple route replies. While it is widely assumed that the set of discovered routes is fairly diverse, an examination of the query propagation behavior reveals that these routes typically have many nodes/links in common. Without sufficient diversity, the routing protocol is limited in its ability to promptly recover from (or even prevent) interrupted service caused by route failures. Based on our understanding of query propagation behavior, we propose a novel mechanism that uses information from terminated query threads to "inject" diversity into the collection of route replies. We study the impact of our diversity injection scheme on the demanding ad-hoc networking environment. Our results demonstrate how diversity injection can leverage a small investment of temporary cache to reduce both the rate of route failures and the bandwidth consumed by overhead query traffic.

The zone routing protocol (ZRP) is a hybrid routing protocol that proactively maintains routes within a local region of the network (which we refer to as the routing zone). Knowledge of this routing zone topology is leveraged by the ZRP to improve the efficiency of a reactive route query/reply mechanism. The ZRP can be configured for a particular network through adjustment of a single parameter, the routing zone radius. We address the issue of configuring the ZRP to provide the best performance for a particular network at any time. Previous work has demonstrated that an optimally configured ZRP operates at least as efficiently as traditional reactive flood-search or proactive distance vector/link state routing protocols (and in many cases, much more efficiently). Adaptation of the ZIP to changing network conditions requires both an understanding of how the ZRP reacts to changes in network behavior and a mechanism to allow individual nodes to identify these changes given only limited knowledge of the network behavior. We demonstrate the effects of relative node velocity, node density, network span, and user data activity on the performance of the ZRP. We then introduce two different schemes ("min searching" and "traffic adaptive") that allow individual nodes to identify and appropriately react to changes in network configuration, based only on information derived from the amount of received ZRP traffic. Through test-bed simulation, we demonstrate that these radius estimation techniques can allow the ZRP to operate within 2% of the control traffic resulting from perfect radius estimation.

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 node's routing zone. By adjusting a single parameter-the size of the routing zone-the ZRP can adapt to a variety of network operational conditions.

In this paper, we study the performance of route query control mechanisms for the recently proposed Zone Routing Protocol (ZRP) for ad-hoc networks. The ZRP proactively maintains routing information for a local neighborhood (routing zone), while reactively acquiring routes to destinations beyond the routing zone. This hybrid routing approach has the potential to be more efficient in the generation of control traffic than traditional routing schemes. However, without proper query control techniques, the ZRP can actually produce more traffic than standard flooding protocols.Our proposed query control schemes exploit the structure of the routing zone to provide enhanced detection (Query Detection (QD1/QD2)), termination (Loop-back Termination (LT), Early Termination (ET)) and prevention (Selective Bordercasting (SBC)) of overlapping queries. We demonstrate how certain combinations of these techniques can be applied to single channel or multiple channel ad-hoc networks to improve both the delay and control traffic performance of the ZRP. Our query control mechanisms allow the ZRP to provide routes to all accessible network nodes with only a fraction of the control traffic generated by purely proactive distance vector and purely reactive flooding schemes, and with a response time as low as 10% of a flooding route query delay.