Showing papers on "Geographic routing published in 2000"

GPSR: greedy perimeter stateless routing for wireless networks

Abstract: We present Greedy Perimeter Stateless Routing (GPSR), a novel routing protocol for wireless datagram networks that uses the positions of routers and a packet's destination to make packet forwarding decisions. GPSR makes greedy forwarding decisions using only information about a router's immediate neighbors in the network topology. When a packet reaches a region where greedy forwarding is impossible, the algorithm recovers by routing around the perimeter of the region. By keeping state only about the local topology, GPSR scales better in per-router state than shortest-path and ad-hoc routing protocols as the number of network destinations increases. Under mobility's frequent topology changes, GPSR can use local topology information to find correct new routes quickly. We describe the GPSR protocol, and use extensive simulation of mobile wireless networks to compare its performance with that of Dynamic Source Routing. Our simulations demonstrate GPSR's scalability on densely deployed wireless networks.

A scalable location service for geographic ad hoc routing

Abstract: GLS is a new distributed location service which tracks mobile node locations. GLS combined with geographic forwarding allows the construction of ad hoc mobile networks that scale to a larger number of nodes than possible with previous work. GLS is decentralized and runs on the mobile nodes themselves, requiring no fixed infrastructure. Each mobile node periodically updates a small set of other nodes (its location servers) with its current location. A node sends its position updates to its location servers without knowing their actual identities, assisted by a predefined ordering of node identifiers and a predefined geographic hierarchy. Queries for a mobile node's location also use the predefined identifier ordering and spatial hierarchy to find a location server for that node.Experiments using the ns simulator for up to 600 mobile nodes show that the storage and bandwidth requirements of GLS grow slowly with the size of the network. Furthermore, GLS tolerates node failures well: each failure has only a limited effect and query performance degrades gracefully as nodes fail and restart. The query performance of GLS is also relatively insensitive to node speeds. Simple geographic forwarding combined with GLS compares favorably with Dynamic Source Routing (DSR): in larger networks (over 200 nodes) our approach delivers more packets, but consumes fewer network resources.

The odd-even turn model for adaptive routing

Abstract: This paper presents a model for designing adaptive wormhole routing algorithms for meshes without virtual channels. The model restricts the locations where some turns can be taken so that deadlock is avoided. In comparison with previous methods, the degree of routing adaptiveness provided by the model is more even for different source-destination pairs. The mesh network may benefit from this feature in terms of communication efficiency. Simulation results show that the even adaptiveness provided by the odd-even turn model makes message routing less vulnerable to nonuniform factors such as hot spot traffic. In addition, this property results in a smaller fluctuation of the network performance with respect to different traffic patterns.

Fisheye state routing: a routing scheme for ad hoc wireless networks

Abstract: This paper presents a novel routing protocol for wireless ad hoc networks-fisheye state routing (FSR). FSR introduces the notion of multi-level fisheye scope to reduce routing update overhead in large networks. Nodes exchange link state entries with their neighbors with a frequency which depends on distance to destination. From link state entries, nodes construct the topology map of the entire network and compute optimal routes. Simulation experiments show that FSR is a simple, efficient and scalable routing solution in a mobile, ad hoc environment.

Systems and methods for determining, collecting, and using geographic locations of internet users

Abstract: A method of determining a geographic location of an Internet user involves determining if the host is on-line, determining ownership of the host name, and then determining the route taken in delivering packets to the user. Based on the detected route, the method proceeds with determining the geographic route based on the host locations and then assigning a confidence level to the assigned location. A system collects the geographic information and allows web sites or other entities to request the geographic location of their visitors. The database of geographic locations may be stored in a central location or, alternatively, may be at least partially located at the web site. With this information, web sites can target content, advertising, or route traffic depending upon the geographic locations of their visitors. Through web site requests for geographic information, a central database tracks an Internet user's traffic on the Internet whereby a profile can be generated. In addition to this profile, the central database can store visitor's preferences as to what content should be delivered to an IP address, the available interface, and the network speed associated with that IP address.

Power-aware localized routing in wireless networks

Abstract: Two metrics where transmission power depends on distance between nodes, and a cost aware metric based on remaining battery power at nodes (assuming constant transmission power), together with corresponding non-localized shortest path routing algorithms, were recently proposed. We define a new power-cost metric based on the combination of both node's lifetime and distance based power metrics. We then propose power, cost, and power-cost GPS based localized routing algorithms, where nodes make routing decisions solely on the basis of location of their neighbors and destination. Power aware localized routing algorithm attempts to minimize the total power needed to route a message between a source and a destination. Cost-aware localized algorithm is aimed at extending battery's worst case lifetime. The combined power-cost algorithm attempts to minimize the total power needed and to avoid nodes with short remaining lifetime. We prove that these localized power, cost, and power-cost efficient routing algorithms are loop-free.

Dynamic routing of bandwidth guaranteed tunnels with restoration

Abstract: This paper presents new algorithms for dynamic routing of restorable bandwidth-guaranteed paths. A straightforward solution for the restoration problem is to find two disjoint paths. However, this results in excessive resource usage for backup paths and does not satisfy the implicit service provider requirement of optimizing network resource utilization so as to increase the number of potential future demands that can be routed. We give an integer programming formulation for this problem which is new. Complete path routing knowledge is a reasonable assumption for a centralized routing algorithm. However, it requires maintenance of non-aggregated or per-path information which is not often desirable particularly when distributed routing is preferred. We show that a partial information scenario which uses only aggregated and not per-path information provides sufficient information for a suitably developed algorithm to be able to perform almost as well as the complete information scenario. In this partial information scenario the routing algorithm only knows what fraction of each link's bandwidth, is currently used by active paths, and is currently used by backup paths. Obtaining this information is feasible using proposed traffic engineering extensions to routing protocols. We formulate the dynamic restorable bandwidth routing problem in this partial information scenario and develop efficient routing algorithms. We compare there routing performance of this algorithm to a bound obtained using complete information. Our partial information-based algorithm performs very well and its performance in terms of the number of rejected requests is very close to the full information bound.

Multipath source routing in wireless ad hoc networks

Abstract: We propose a new multipath routing protocol for ad hoc wireless networks-multipath source routing (MSR), which is based on DSR (dynamic source routing). MSR extends DSR's route discovery and route maintenance mechanism to deal with multipath routing. Based on the measurement of RTT, we propose a scheme to distribute load between multiple paths. The simulation results show that our approach improves the throughput of TCP and UDP and the packet delivery ratio, and reduces the end-to-end delay and the queue size, while adding little overhead. As a result, MSR decreases the network congestion quite well.

Geographic routing for wireless networks

Abstract: Distributed shortest-path routing protocols for wired networks either describe the entire topology of a network or provide a digest of the topology to every router. They continually update the state describing the topology at all routers as the topology changes to find correct routes for all destinations. Hence, to find routes robustly, they generate routing protocol message traffic proportional to the product of the number of routers in the network and the rate of topological change in the network. Current ad-hoc routing protocols, designed specifically for mobile, wireless networks, exhibit similar scaling properties. It is the reliance of these routing protocols on state concerning all links in the network, or all links on a path between a source and destination, that is responsible for their poor scaling. We present Greedy Perimeter Stateless Routing (GPSR), a novel routing protocol for wireless datagram networks that uses the positions of routers and a packet's destination to make packet forwarding decisions. GPSR makes greedy forwarding decisions using only information about a router's immediate neighbors in the network topology. When a packet reaches a region where greedy forwarding is impossible, the algorithm recovers by routing around the perimeter of the region. By keeping state only about the local topology, GPSR scales better in per-router state than shortest-path and ad-hoc routing protocols as the number of network destinations increases. Under mobility's frequent topology changes, GPSR can use local topology information to find correct new routes quickly. We describe the GPSR protocol, and use extensive simulation of mobile wireless networks to compare its performance with that of Dynamic Source Routing. Our simulations demonstrate GPSR's scalability on densely deployed wireless networks.

Location based routing for mobile ad-hoc networks

Abstract: In an ad-hoc mobile network, a geometry-based routing algorithm (GRA) is used to route traffic from a source node to a destination node. In the GRA, a source node maintains location information and routing information for all nodes in a local area and approximate location information for at least some nodes outside the local area. If the source node has to send a packet to a destination node outside their local area, then the source node uses the approximate location information of the destination node to identify which node in its local area is closer to the destination node than the source node. The source node then sends the packet to the identified local node for further routing.

IP layer restoration and network planning based on virtual protection cycles

Abstract: We describe a novel restoration strategy called virtual protection cycles (p-cycles, patents pending) for extremely fast restoration in IP networks. Originally conceived for use in WDM and Sonet transport networks, we outline the adaption of the p-cycle concept to an IP environment. In an IP router-based network, p-cycles are implemented with virtual circuits techniques (such as an MPLS label switched path, or other means) to form closed logical loops that protect a number of IP links, or a node. In the event of failure, packets which would normally have been lost are encapsulated with a p-cycle IP address and reenter the routing table, which diverts them onto a protection cycle. They travel by normal forwarding or label switching along the p-cycle until they reach a node where the continuing route cost to the original destination is lower than that at the p-cycle entry node. Diverted packets are deencapsulated (dropped from the p-cycle) at that node and follow a normal (existing) route from there to their destination. Conventional routing protocols such as OSPF remain in place and operate as they do today, to develop a longer term global update to routing tables. Diversionary flows on the p-cycle inherently cease when the global routing update takes effect in response to the failed link or node. The p-cycle thus provides an immediate real-time detour, preventing packet loss, until conventional global routing reconvergence occurs. The aim of the paper is to explain the basic p-cycle concept and its adaptation to both link and node restoration in the IP transport layer, and to outline certain initial results on the problem of optimized design of p-cycle based IP networks.

Route updating in ad-hoc networks

Abstract: In conventional ad-hoc networks using reactive routing protocols the route between the source node and the destination node is not updated until the route is actually broken. In response to predetermined events a request for updated route message can be sent to the destination node to determine if another route exists between the source node and the destination node. A reply to the request for updated route can be provided by either the destination node or by a node which has a cached route between the source node and the destination node. This updated route request scheme can be implemented in networks which use source routing and networks which use distance vector routing.

Routing method for traffic load distribution in packet-switched network

Abstract: The present invention relates to a routing method for a traffic load distribution in a packet-switched network., which method includes a first step for computing an average cost between the start node and a plurality of nodes stored in a routing table and selecting a node having a cost lower than an average cost value K as a candidate of an intermediate node; a second step for randomly selecting one among the intermediate node candidates when a packet to be transmitted from the start node is generated and determining the selected node as an intermediate node of the packet; a third step for storing an information with respect to a path setting bit(b) a destination node address and intermediate node address in a header region of the packet and transmitting the packet to the intermediate node through the path of the lowest cost using the information stored in the routing table; and a fourth step for transmitting the packet to the destination node through the lowest cost path using the information stored in the routing table when the packet arrives at the intermediate node, for thereby diversifying data transmission path using an intermediate node address by providing an intermediate node address to a packet separately from a destination node address for thereby effectively distributing data traffic in a packet-switched network.

Scalable unidirectional routing with zone routing protocol (ZRP) extensions for mobile ad-hoc networks

Abstract: Ad-hoc networks consist of peer-to-peer communicating nodes that are highly mobile. As such, an ad-hoc network lacks infrastructure and the topology of the network changes dynamically. The task of routing data from a source to a destination in such a network is challenging. Several routing protocols have been proposed for wireless ad-hoc networks. Most of these protocols, however, pre-suppose the presence of bi-directional links between the nodes in the network. In reality the ad-hoc network may consist of heterogeneous nodes with different power capabilities and hence, different transmission ranges. When this is the case, a given node might be able to receive the transmission of another given node but might not be able to successfully transmit to the latter. Thus, unidirectional links are formed. Most of the current routing protocols are unsuitable for deployment when such unidirectional links are present. We consider a routing protocol called the zone routing protocol (ZRP) that has been proposed for wireless ad-hoc networks with bi-directional links. The zone routing protocol employs a hybrid proactive (table driven) and reactive (on-demand) methodology to provide scalable routing in the ad-hoc network. However, in the presence of unidirectional links some routes remain undiscovered if ZRP is used. We propose extensions to ZRP to support its deployment when unidirectional links are present. In particular, we propose a query enhancement mechanism that recursively builds partial routes to a destination. Simulation results show that even at a high mobility of 20 m/s, the queries resulting due to the enhancement mechanism result in the computation of valid routes more than 80% of the time. These results are valid even when a large number (40% of nodes have half the transmission range as that of the remaining nodes) of unidirectional links are present in the network.

Landmark routing for large ad hoc wireless networks

Abstract: We present an enhanced version of the routing protocol, Landmark Ad Hoc Routing (LANMAR). LANMAR combines the features of Fisheye State Routing (FSR) and Landmark routing. The enhanced version features landmark election to cope with the dynamic and mobile environment. Other advantages of LANMAR include the use of landmarks for each logical group (e.g., a team of co-workers at a convention or a tank battalion in the battlefield) in order to reduce routing update overhead in large networks, and the exchanging of neighborhood link state only with neighbors. When the network size grows, remote groups of nodes are "summarized" by the corresponding landmarks. As a result, each node will maintain accurate routing information about immediate neighborhood; at the same time it will keep track of the routing directions to the landmark nodes and thus, to remote groups. Simulation experiments show that the enhanced version suffers some performance degradation at steady state because of election overhead. However, it still provides an efficient and scalable routing solution in a mobile, ad hoc environment. Moreover, the election provides a much needed recovery from landmark failures.

Depth first search and location based localized routing and QoS routing in wireless networks

Abstract: In a localized routing algorithm, node A currently holding the message forwards it based on the location of itself, its neighboring nodes and destination. We propose to use depth first search (DFS) method for routing decisions. Each node A, upon receiving the message for the first time, sorts all its neighbors according to a criteria such as their distance to destination and uses that order in DFS algorithm. It is the first localized algorithm that guarantees delivery for (connected) wireless networks modeled by arbitrary graphs, including inaccurate location information. We then propose the first localized QoS routing algorithm for wireless networks. It performs DFS routing algorithm after edges with insufficient bandwidth or insufficient connection time are deleted from the graph, and attempts to minimize hop count. This is also the first paper to apply GPS in QoS routing decisions, and to consider the connection time (estimated lifetime of a link) as a QoS criterion. The average length of measured QoS path in our experiments, obtained by DFS method, was between 1 and 1.34 times longer than the length of QoS path obtained by shortest path algorithm. The overhead is considerably reduced by applying the concept of internal nodes.

Methods and systems for routing messages in a communications network

Abstract: A flexible routing node for re-directing signaling messages in a communications network is disclosed. Re-direction or re-routing of signaling message packets is accomplished through the use of a range or block based database in conjunction with an exception-based database. The range-based routing instruction databases incorporate a data structure that maps ranges or blocks of mobile identification numbers (MINs) to a single destination network address, while the exceptions database stores any exceptions to these range or block-based rules. The pair of routing databases is implemented such that, when a signaling message is received that requires re-direction, the exception-based database is queried first. If a match is found in the exceptions database, the signaling message is modified using the returned routing instructions and transmitted into an associated communication network. If no match is found in the exception-based database, a default query is performed against the range-based database. The signaling message is then modified using the routing instructions returned by the range-based database and transmitted into an associated communication network.

On scalable QoS routing: performance evaluation of topology aggregation

Abstract: A number of important questions remain concerning the scalability of networks with quality of service guarantees. We consider one of these questions: can QoS routing protocols scale to large networks? To address this question, we evaluate the performance of techniques that can reduce the QoS routing protocol overhead. We specifically focus on topology aggregation, which can reduce overhead by orders of magnitude. We also investigate the interaction of topology aggregation with other important factors that contribute to performance, such as routing update frequency, routing algorithms, and network configuration. Our experiments are based on simulations of relatively large, structured networks. Among our observations, we find-contrary to intuition-that topology aggregation does not always have a negative impact on routing performance. Aggregation can reduce the routing information fluctuation, increase stability, and thus benefit routing performance. We also propose two new methods of aggregating routing information. Our hybrid aggregation method performs much better than conventional star aggregation and approaches unaggregated performance. Our weighted aggregation method, while intuitively appealing, offers mixed performance across topologies.

On distributed, geographic-based packet routing for LEO satellite networks

Abstract: Advances in satellite technology are enabling the deployment of large constellations of low Earth Orbiting (LEO) satellites. Next-generation systems will be tailored for broadband, packet-switched services, and therefore require either distributed or centralized packet routing mechanisms. Some researchers have hypothesized that the semi-regular mesh topology of a polar-orbiting constellation admits a simple distributed routing protocol based on using geographic information embedded in the node address. We take a closer look at this hypothesis in the context of commercially-proposed constellation designs. Using simulation, we study a distributed routing protocol that selects the next hop based on a minimization of the remaining distance to the destination. Our numerical results indicate that this routing strategy usually yields good routes, with an average latency degradation of less than 10 ms when compared with the optimal route. However, there are locations in the topology, most notably around the counter-rotating seams, the polar regions, and close to the destination of a packet, where the assumption of a regular mesh topology breaks down and it is difficult to guarantee robustness without adding significant additional complexity to the protocol.

Datagram routing algorithm for LEO satellite networks

Abstract: Satellite networks provide global coverage and support a wide range of services. Low-Earth-orbit (LEO) satellites provide short round-trip delays and are becoming increasingly important. One of the challenges in LEO satellite networks is the development of specialized and efficient routing algorithms. In this work, a datagram routing algorithm for LEO satellite networks is introduced. The algorithm generates minimum propagation delay paths. The performance of the algorithm is evaluated through simulations and finally robustness issues are discussed.

High-performance routing in networks of workstations with irregular topology

Abstract: Networks of workstations are rapidly emerging as a cost-effective alternative to parallel computers. Switch-based interconnects with irregular topology allow the wiring flexibility, scalability, and incremental expansion capability required in this environment. However, the irregularity also makes routing and deadlock avoidance on such systems quite complicated. In current proposals, many messages are routed following nonminimal paths, increasing latency and wasting resources. In this paper, we propose two general methodologies for the design of adaptive routing algorithms for networks with irregular topology. Routing algorithms designed according to these methodologies allow messages to follow minimal paths in most cases, reducing message latency and increasing network throughput. As an example of application, we propose two adaptive routing algorithms for ANI (previously known as Autonet). They can be implemented either by duplicating physical channels or by splitting each physical channel into two virtual channels. In the former case, the implementation does not require a new switch design. It only requires changing the routing tables and adding links in parallel with existing ones, taking advantage of spare switch ports. In the latter case, a new switch design is required, but the network topology is not changed. Evaluation results for several different tapologies and message distributions show that the new routing algorithms are able to increase throughput for random traffic by a factor of up to 4 with respect to the original up*/down* algorithm, also reducing latency significantly. For other message distributions, throughput is increased more than seven times. We also show that most of the improvement comes from the use of minimal routing.

An adaptive routing algorithm for wavelength-routed optical networks with a distributed control scheme

Abstract: For a wavelength-routed network in which connection requests are arriving and departing at high rates, an appropriate control scheme must be implemented to set up light paths for each request in a fast and efficient manner. The control scheme, which includes routing and wavelength assignment algorithms, must also be scalable, and should attempt to minimize the number of blocked connections. In this paper, we consider a distributed control scheme which utilizes a new adaptive routing approach called alternate-link routing. In the proposed approach, routing decisions for a light path are made adaptively on a hop-by-hop basis by individual nodes in a distributed manner. The scheme does not require the maintenance of any global information. A simulation is developed to analyze blocking performance, and it is shown that the proposed approach outperforms fixed routing and, under certain conditions, also outperforms fixed alternate-path routing.

Networks with cognitive packets

Abstract: Based on our earlier work ("Towards networks with intelligent packets", Proc. 14th Int. Symp. on Computer and Information Sciences, p. 1-11, Oct. 1999), we discuss packet networks in which intelligent capabilities for routing and flow control are concentrated in the packets, rather than in the nodes and protocols. This paper describes a possible testbed to test and evaluate their capabilities, and presents an analytical model for the worst and best case performance of such systems.

A New Methodology to Computer Deadlock-Free Routing Tables for Irregular Networks

Abstract: Networks of workstations (NOWs) are being considered as a cost-effective alternative to parallel computers Many NOWs are arranged as a switch-based network with irregular topology, which makes routing and deadlock avoidance quite complicated Current proposals use the up*/down* routing algorithm to remove cyclic dependencies between channels and avoid deadlock However, routing is considerably restricted and most messages must follow non-minimal paths, increasing latency and wasting resources In this paper, we propose a new methodology to compute deadlock-free routing tables for NOWs The methodology tries to minimize the limitations of the current proposals in order to improve network performance It is based on generating an underlying acyclic connected graph from the network graph and assigning a sequence number to each switch, which is used to remove cyclic dependencies Evaluation results show that the routing algorithm based on the new methodology increases throughput by a factor of up to 2 in large networks, also reducing latency significantly

Methods and apparatus for routing in a mobile ad hoc network

Abstract: A “peer-to-peer” hierarchical routing protocol—also referred to as Zone-based Hierarchical Link State Routing protocol (or “ZHLS”)—which incorporates location information into a novel “peer-to-peer” hierarchical routing approach. The network may be divided into non-overlapping zones. Aggregating nodes into zones conceals the detail of the network topology. Initially, each node knows its own position and therefore zone ID through a position determination unit, such as a Global Positioning System (GPS). After the network is established, each node knows the low level (node level) topology about node connectivity within its zone and the high level (zone level) topology about zone connectivity of the whole network. A packet may be forwarded by specifying the hierarchical address—zone ID and node ID—of a destination node in the packet header.

Fault-tolerant adaptive and minimal routing in mesh-connected multicomputers using extended safety levels

Abstract: The minimal routing problem in mesh-connected multicomputers with faulty blocks is studied. Two-dimensional meshes are used to illustrate the approach. A sufficient condition for minimal routing in 2D meshes with faulty blocks is proposed. Unlike many traditional models that assume all the nodes know global fault distribution, our approach is based on the concept of an extended safety level, which is a special form of limited fault information. The extended safety level information is captured by a vector associated with each node. When the safety level of a node reaches a certain level (or meets certain conditions), a minimal path exists from this node to any nonfaulty nodes in 2D meshes. Specifically, we study the existence of minimal paths at a given source node, limited distribution of fault information, and minimal routing itself. We propose three fault-tolerant minimal routing algorithms which are adaptive to allow all messages to use any minimal path. We also provide some general ideas to extend our approaches to other low-dimensional mesh-connected multicomputers such as 2D tori and 3D meshes. Our approach is the first attempt to address adaptive and minimal routing in 2D meshes with faulty blocks using limited fault information.

Improving the Up*/Down* Routing Scheme for Networks of Workstations

Abstract: Networks of workstations (NOWs) are being considered as a cost-effective alternative to parallel computers. Many NOWs are arranged as a switch-based network with irregular topology, which makes routing and deadlock avoidance quite complicated. Current proposals use the up*/down* routing algorithm to remove cyclic dependencies between channels and avoid deadlock. Recently, a simple and effective methodology to compute up*/down* routing tables has been proposed by us. The resulting up*/down* routing scheme makes use of a different link direction assignment to compute routing tables. Assignment of link direction is based on generating an underlying acyclic connected graph from the network graph. In this paper, we propose and evaluate new heuristic rules to compute the underlying graph. Moreover, we propose a traffic balancing algorithm to obtain more efficient up*/down* routing tables when source routing is used. Evaluation results show that the routing algorithm based on the new methodology increases throughput by a factor of up to 2.8 in large networks, also reducing latency significantly.

A Flexible Routing Scheme for Networks of Workstations

Abstract: NOWs are arranged as a switch-based network which allows the layout of both regular and irregular topologies. However, the irregular pattern interconnect makes routing and deadlock avoidance quite complicated. Current proposals use the up*/down* routing algorithm to remove cyclic dependencies between channels and avoid deadlock. Recently, a simple and effective methodology to compute up*/down* routing tables has been proposed by us. The resulting routing algorithm is very effective in irregular topologies. However, its behavior is very poor in regular networks with orthogonal dimensions. Therefore, we propose a more flexible routing scheme that is effective in both regular and irregular topologies. Unlike up*/down* routing algorithms, the proposed routing algorithm breaks cycles at different nodes for each direction in the cycle, thus providing better traffic balancing than that provided by up*/down* routing algorithms. Evaluation results modeling a Myrinet network show that the new routing algorithm increases throughput with respect to the original up*/down* routing algorithm by a factor of up to 3:5 for regular networks, also maintaining the performance of the improved up*/down* routing scheme proposed in [7] when applied to irregular networks.

Routing in All-Optical Networks: Algorithmic and Graph-Theoretic Problems

Abstract: This paper surveys theoretical results for wavelength—routing in all—optical networks and presents several open problems. We focus our attention on graph-theoretical problems and proof techniques.

Quality of service routing in ad hoc networks

Abstract: Current generation routing protocols for ad hoc networks typically use shortest path routing. Examples include on-demand routing protocols such as DSR and AODV. All these protocols can support only the best-effort data traffic, but the quality of service (QoS) requirements, such as delay, packet loss and bandwidth requirements are not supported. In the wireline networks such as ATM, QoS routing has been studied extensively. Due to dynamic nature of ad hoc networks owing to mobility and varying radio link conditions, the available state of information is never precise, and consequently, we cannot directly apply the traditional wireline QoS routing algorithms. Soft QoS without hard guarantees is explored here. Previous work in QoS routing in ad hoc networks is reported by Chen and Nahrstedt (see IEEE journal on Selected Areas in Communication, 1999), where delay and bandwidth constrained QoS routing were studied separately. The uncertainty was handled using a deterministic model. The algorithms developed in this paper accommodate imprecise state information. Fuzzy logic is a well recognized technique for modeling imprecision. A rule based fuzzy logic model is used to describe imprecise state information. Delay constraints are considered here in finding feasible routes (paths). Among feasible paths, optimal path (least cost path) is found using hop count as a performance measure. In case of re-routing, sub-optimal paths are found using the same performance measure.