An ad-hoc network is the cooperative engagement of a collection of Mobile Hosts without the required intervention of any centralized Access Point. In this paper we present an innovative design for the operation of such ad-hoc networks. The basic idea of the design is to operate each Mobile Host as a specialized router, which periodically advertises its view of the interconnection topology with other Mobile Hosts within the network. This amounts to a new sort of routing protocol. We have investigated modifications to the basic Bellman-Ford routing mechanisms, as specified by RIP [5], to make it suitable for a dynamic and self-starting network mechanism as is required by users wishing to utilize adhoc networks. Our modifications address some of the previous objections to the use of Bellman-Ford, related to the poor looping properties of such algorithms in the face of broken links and the resulting time dependent nature of the interconnection topology describing the links between the Mobile Hosts. Finally, we describe the ways in which the basic network-layer routing can be modified to provide MAC-layer support for ad-hoc networks.

We present a new distributed routing protocol for mobile, multihop, wireless networks. The protocol is one of a family of protocols which we term "link reversal" algorithms. The protocol's reaction is structured as a temporally-ordered sequence of diffusing computations; each computation consisting of a sequence of directed l i nk reversals. The protocol is highly adaptive, efficient and scalable; being best-suited for use in large, dense, mobile networks. In these networks, the protocol's reaction to link failures typically involves only a localized "single pass" of the distributed algorithm. This capability is unique among protocols which are stable in the face of network partitions, and results in the protocol's high degree of adaptivity. This desirable behavior is achieved through the novel use of a "physical or logical clock" to establish the "temporal order" of topological change events which is used to structure (or order) the algorithm's reaction to topological changes. We refer to the protocol as the Temporally-Ordered Routing Algorithm (TORA).

Efficient routing among a set of mobile hosts (also called nodes) is one of the most important functions in ad-hoc wireless networks. Routing based on a connected dominating set is a promising approach, where the searching space for a route is reduced to nodes in the set. A set is dominating if all the nodes in the system are either in the set or neighbors of nodes in the set. In this paper, we propose a simple and efficient distributed algorithm for calculating connected dominating set in adhoc wireless networks, where connections of nodes are determined by their geographical distances. We also propose an update/recalculation algorithm for the connected dominating set when the topology of the ad hoc wireless network changes dynamically. Our simulation results show that the proposed approach outperforms a classical algorithm in terms of finding a small connected dominating set and doing so quickly. Our approach can be potentially used in designing efficient routing algorithms based on a conne...

The conventional approach to routing in computer networks consists of using a heuristic to compute a single shortest path from a source to a destination. Single-path routing is very responsive to topological and link-cost changes; however, except under light traffic loads, the delays obtained with this type of routing are far from optimal. Furthermore, if link costs are associated with delays, single-path routing exhibits oscillatory behavior and becomes unstable as traffic loads increase. On the other hand, minimumdelay routing approaches can minimize delays only when traffic is stationary or very slowly changing. We present a "near-optimal" routing framework that offers delays comparable to those of optimal routing and that is as flexible and responsive as single-path routing protocols proposed to date. First, an approximation to the Gallager's minimum-delay routing problem is derived, and then algorithms that implement the approximation scheme are presented and verified. We introdu...

algorithm converge very slowly to the correct routes when link costs increase, and in the case when a set of link failures results in a network partition, DBF simply fails to converge, a problem which is commonly referred to as the count-to-infinity problem. In this paper, we present the first distance vector routing algorithm MDVA that uses a set of loop-free invariants to prevent the count-to-infinity problem. MDVA, in addition, computes multipaths that are loop-free at every instant. In our earlier work we shows how such loop-free multipaths can be used in traffic load-balancing and minimizing delays, which otherwise are impossible to perform in current single-path routing algorithms [15].

As internets grow, both in size and in the diversity of routing requirements, providing interdomain routing that can accommodate both of these factors becomes increasingly crucial. The combinatorial explosion of mixing and matching different routing criteria weighs heavily on the mechanisms provided by conventional hop-by-hop routing architectures. We expect that over the next 5 to 10 years, the types of services available will continue to evolve and that specialized facilities will be employed to provide new services. While the number and variety of routes provided by hopby -hop routing architectures with type of service support (i.e., multiple, tagged routes) may be sufficient for a large percentage of traffic, it is important that mechanisms be in place to support efficient routing of specialized traffic types via special routes. Our desire to support special routes efficiently led us to investigate the dynamic installation of routes ([Breslau-Estrin 91, Clark 90, IDPR90]). In a pre...

We present and verify ROAM, an on-demand routing algorithm that maintains multiple loop-free paths to destinations. Each router maintains entries only for those destinations for which data flows through the router, which reduces storage space requirements and the amount of bandwidth needed to maintain correct routing tables. In ROAM, routes are established and maintained on demand using diffusing computations. A router does not send updates for active destinations, unless its distance to them increases beyond a given threshold. ROAM maintains state that informs routers when a destination is unreachable and prevents routers from sending unnecessary search packets attempting to find paths to an unreachable destination. ROAM is shown to converge in a finite time after an arbitrary sequence of topological changes and is shown to be loop-free at every instant. The time and communication complexities of ROAM are analyzed. Keywords--- On-demand, Loop-Free Routing, Distance vector routing I....

We present a relative performance comparison of the Temporally-Ordered Routing Algorithm (TORA) with an Ideal Link State (ILS) routing algorithm. The performance metrics evaluated include bandwidth efficiency for both control and data, as well as end-to-end message packet delay and throughput. The routing algorithms are compared in the context of a dynamic, multihop, wireless network employing broadcast transmissions. The network parameters varied include network size, average rate of topological changes and average network connectivity. While the average network connectivity was found not to be a significant factor, the relative performance of TORA and ILS was found to be critically dependent on the network size, and average rate of topological changes. The results further indicate that for a given available bandwidth---as either the size of network increases or the rate of network topological change increases, the performance of TORA eventually exceeds that of ILS.

We compare the performance of two recently proposed distance--vector algorithms (Merlin-- Segall and Extended Bellman--Ford) with a link--state algorithm (SPF), under varying file transfer workload. (Unlike the traditional distance--vector algorithms, these new distance-- vector algorithms do not suffer from long--lived loops.) Our comparison is done using a recently developed network simulator, MaRS. We consider both dynamic and static file transfer connections, and both uniform and hotspot distributions of source--sink pairs. Our conclusion is that Extended Bellman--Ford performs as well as SPF in terms of delay and throughput. This suggests that distance--vector algorithms are appropriate for very large wide--area networks, since their space requirements are less than that of link-state algorithms. 1 Introduction In wide--area store--and--forward computer networks, routing protocols are responsible for forwarding data packets over good routes which optimize real--time performance ...

We examine two approaches to adaptive routing protocols for wide-area store-and-forward networks, namely, distance-vector and link-state. Distance-vector algorithms have less storage requirements than link-state algorithms. The ARPANET started with a distance-vector algorithm (Distributed Bellman-Ford), but because of long-lived loops, changed to a link-state algorithm (SPF). We evaluate, using a recently developed network simulator, MaRS, the transient and steady-state performance of SPF and two newly proposed distance-vector algorithms (ExBF and MS). Overall, SPF and ExBF have comparable performance and MS is worse.