Showing papers on "Multipath routing published in 1997"

Associativity-Based Routing for Ad Hoc Mobile Networks

Abstract: This paper presents a new, simple and bandwidth-efficient distributed routing protocol to support mobile computing in a conference size ad-hoc mobile network environment. Unlike the conventional approaches such as link-state and distance-vector distributed routing algorithms, our protocol does not attempt to consistently maintain routing information in every node. In an ad-hoc mobile network where mobile hosts (MHs) are acting as routers and where routes are made inconsistent by MHs‘ movement, we employ an associativity-based routing scheme where a route is selected based on nodes having associativity states that imply periods of stability. In this manner, the routes selected are likely to be long-lived and hence there is no need to restart frequently, resulting in higher attainable throughput. Route requests are broadcast on a per need basis. The association property also allows the integration of ad-hoc routing into a BS-oriented Wireless LAN (WLAN) environment, providing the fault tolerance in times of base stations (BSs) failures. To discover shorter routes and to shorten the route recovery time when the association property is violated, the localised-query and quick-abort mechanisms are respectively incorporated into the protocol. To further increase cell capacity and lower transmission power requirements, a dynamic cell size adjustment scheme is introduced. The protocol is free from loops, deadlock and packet duplicates and has scalable memory requirements. Simulation results obtained reveal that shorter and better routes can be discovered during route re-constructions.

Small forwarding tables for fast routing lookups

Abstract: For some time, the networking community has assumed that it is impossible to do IP routing lookups in software fast enough to support gigabit speeds. IP routing lookups must find the routing entry with the longest matching prefix, a task that has been thought to require hardware support at lookup frequencies of millions per second.We present a forwarding table data structure designed for quick routing lookups. Forwarding tables are small enough to fit in the cache of a conventional general purpose processor. With the table in cache, a 200 MHz Pentium Pro or a 333 MHz Alpha 21164 can perform a few million lookups per second. This means that it is feasible to do a full routing lookup for each IP packet at gigabit speeds without special hardware.The forwarding tables are very small, a large routing table with 40,000 routing entries can be compacted to a forwarding table of 150-160 Kbytes. A lookup typically requires less than 100 instructions on an Alpha, using eight memory references accessing a total of 14 bytes.

A cluster-based approach for routing in dynamic networks

Abstract: The design and analysis of routing protocols is an important issue in dynamic networks such as packet radio and ad-hoc wireless networks Most conventional protocols exhibit their least desirable behavior for highly dynamic interconnection topologies We propose a new methodology for routing and topology information maintenance in dynamic networks The basic idea behind the protocol is to divide the graph into a number of overlapping clusters A change in the network topology corresponds to a change in cluster membership We present algorithms for creation of clusters, as well as algorithms to maintain them in the presence of various network events Compared to existing and conventional routing protocols, the proposed cluster-based approach incurs lower overhead during topology updates and also has quicker reconvergence The effectiveness of this approach also lies in the fact that existing routing protocols can be directly applied to the network --- replacing the nodes by clusters

On path selection for traffic with bandwidth guarantees

Abstract: Transmission of multimedia streams imposes a minimum-bandwidth requirement on the path being used to ensure end-to-end Quality-of-Service (QoS) guarantees. While any shortest-path algorithm can be used to select a feasible path, additional constraints that limit resource consumption and balance the network load are needed to achieve efficient resource utilization. We present a systematic evaluation of four routing algorithms that offer different tradeoffs between limiting the path hop count and balancing the network load. Our evaluation considers not only the call blocking rate but also the fairness to requests for different bandwidths, robustness to inaccurate routing information, and sensitivity to the routing information update frequency. It evaluates not only the performance of these algorithms for the sessions with bandwidth guarantees, but also their impact on the lower priority best-effort sessions. Our results show that a routing algorithm that gives preference to limiting the hop count performs better when the network load is heavy, while an algorithm that gives preference to balancing the network load performs slightly better when the network load is light. We also show that the performance of using pre-computed paths with a few discrete bandwidth requests is comparable to that of computing paths on-demand, which implies feasibility of class-based routing. We observe that the routing information update interval can be set reasonably large to reduce routing overhead without sacrificing the overall performance, although an increased number of sessions can be misrouted.

Internet routing instability

Abstract: This paper examines the network inter-domain routing information exchanged between backbone service providers at the major U.S. public Internet exchange points. Internet routing instability, or the rapid fluctuation of network reachability information, is an important problem currently facing the Internet engineering community. High levels of network instability can lead to packet loss, increased network latency and time to convergence. At the extreme, high levels of routing instability have lead to the loss of internal connectivity in wide-area, national networks. In this paper, we describe several unexpected trends in routing instability, and examine a number of anomalies and pathologies observed in the exchange of inter-domain routing information. The analysis in this paper is based on data collected from BGP routing messages generated by border routers at five of the Internet core's public exchange points during a nine month period. We show that the volume of these routing updates is several orders of magnitude more than expected and that the majority of this routing information is redundant, or pathological. Furthermore, our analysis reveals several unexpected trends and ill-behaved systematic properties in Internet routing. We finally posit a number of explanations for these anomalies and evaluate their potential impact on the Internet infrastructure.

QoS based routing in networks with inaccurate information: theory and algorithms

Abstract: We investigate the problem of routing connections with QoS requirements across one or more networks, when the information available for making routing decisions is inaccurate and expressed in some probabilistic manner. This uncertainty about the actual state of a node or network arises naturally in a number of different environments, that are reviewed in the paper. The main focus is to determine the impact of such inaccuracies on the path selection process, whose goal is then to identify the path that is most likely to satisfy the QoS requirements.

Ants and reinforcement learning: a case study in routing in dynamic networks

Abstract: We investigate two new distributed routing algorithms for data networks based on simple biological "ants" that explore the network and rapidly learn good routes, using a novel variation of reinforcement learning. These two algorithms are fully adaptive to topology changes and changes in link costs in the network, and have space and computational overheads that are competitive with traditional packet routing algorithms: although they can generate more routing traffic when the rate of failures in a network is low, they perform much better under higher failure rates. Both algorithms are more resilient than traditional algorithms, in the sense that random corruption of routing state has limited impact on the computation of paths. We present convergence theorems for both of our algorithms drawing on the theory of non-stationary and stationary discrete-time Markov chains over the reals. We present an extensive empirical evaluation of our algorithms on a simulator that is widely used in the computer networks community for validating and testing protocols. We present comparative results on data delivery performance, aggregate routing traffic (algorithm overhead), as well as the degree of resilience for our new algorithms and two traditional routing algorithms in current use. We also show that the performance of our algorithms scale well with increase in network size-using a realistic topology.

Quality-of-Service Routing for Traffic with Performance Guarantees

Abstract: Quality-of-Service (QoS) routing tries to select a path that satisfies a set of QoS constraints, while also achieving overall network resource efficiency. We present initial results on QoS path selection for traffic requiring bandwidth and delay guarantees. For traffic with bandwidth guarantees, we found that several routing algorithms that favor paths with fewer hops perform well. For traffic with delay guarantees, we show that for a broad class of WFQ-like scheduling algorithms, the problem of finding a path satisfying bandwidth, delay, delay-jitter, and/or buffer space constraints while at the same time deriving the bandwidth that has to be reserved to meet these constraints, is solvable by a modified version of the Bellman-Ford shortest-path algorithm in polynomial time.

Performance of alternate routing methods in all-optical switching networks

Abstract: We study routing methods in all-optical switching networks. In all-optical switching networks, the connection with more hops encounters more call blocking, and it is especially true in optical networks with no wavelength conversions. We therefore consider an alternate routing method with limited trunk reservation in which connections with more hops are prepared more alternate routes. Through developing an approximate analytic approach, we show that our method keeps good performance when compared with the existing alternate routing methods, and also that the fairness among connections can be improved. Further performance improvement is investigated by introducing a wavelength assignment policy and a dynamic routing method. An effectiveness of the proposed method is investigated through simulation.

A protocol for scalable loop-free multicast routing

Abstract: In network multimedia applications such as multiparty teleconferencing, users often need to send the same information to several (but not necessarily all) other users. To manage such one-to-many or many-to-many communication efficiently in wide-area internetworks, it is imperative to support and perform multicast routing. Multicast routing sends a single copy of a message from a source to multiple receivers over a communication link that is shared by the paths to the receivers. Loop-freedom is an especially important consideration in multicasting because applications using multicasting tend to be multimedia and bandwidth intensive, and loops in multicast routing duplicate looping packets. We present and verify a new multicast routing protocol, called multicast Internet protocol (MIP), which offers a simple and flexible approach to constructing both group-shared and shortest-paths multicast trees. MIP can be sender-initiated or receiver-initiated or both; therefore, it can be tailored to the particular nature of an application's group dynamics and size. MIP is independent of the underlying unicast routing algorithms used. MIP is robust and adapts under dynamic network conditions (topology or link cost changes) to maintain loop-free multicast routing. Under stable network conditions, MIP has no maintenance or control message overhead. We prove that MIP is loop-free at every instant, and that it is deadlock-free and obtains multicast routing trees within a finite time after the occurrence of an arbitrary sequence of topology or unicast changes.

A system and traffic dependent adaptive routing algorithm for ad hoc networks

Abstract: An ad hoc network consists of a number of mobile hosts who communicate with each other over a wireless channel without any centralized control. The basic problem is to obtain a distributed routing scheme so that under the network connectivity assumption any mobile host can transmit/receive data from any other host in the network. In this paper we propose a new routing algorithm for ad hoc networks. The proposed algorithm uses a more appropriate distance measure given by the expected delay along a path, instead of the number of hops used in most of the existing algorithms. This metric allows the algorithm to adapt to changes not only in the topology of the network, but also in the traffic intensity. The algorithm uses a novel technique for estimating the path delays without requiring the links to be bidirectional or the clocks at the nodes in the network to be synchronized. The proposed algorithm is able to perform both reliable and good routing with low communication overhead and computational requirements.

Dual Reinforcement Q-Routing: An On-Line Adaptive Routing Algorithm

Abstract: This paper describes and evaluates the Dual Reinforcement Q-Routing algorithm (DRQ-Routing) for adaptive packet routing in communication networks. Each node in the network has a routing decision maker that adapts, on-line, to learn routing policies that can sustain high network loads and have low average packet delivery time. These decision makers learn based on the information they get back from their neighboring nodes as they send packets to them (forward exploration similar to Q-Routing) and the information appended to the packets they receive from their neighboring nodes (backward exploration unique to DRQ-Routing). Experiments over several network topologies have shown that at low loads, DRQ-Routing learns the optimal policy more than twice as fast as Q-Routing, and at high loads, it learns routing policies that are more than twice as good as Q-Routing in terms of average packet delivery time. Further, DRQ-Routing is able to sustain higher network loads than Q-Routing and non-adaptive shortest-path routing.

Reducing the cost of security in link-state routing

Abstract: Security in link-state routing protocols is a feature that is both desirable and costly. This paper examines the cost of security and presents two techniques for efficient and secure processing of link state updates. The first technique is geared towards a relatively stable internetwork environment while the second is designed with a more volatile environment in mind.

Compressionless routing: a framework for adaptive and fault-tolerant routing

Abstract: Compressionless routing (CR) is an adaptive routing framework which provides a unified framework for efficient deadlock free adaptive routing and fault tolerance. CR exploits the tight coupling between wormhole routers for flow control to detect and recover from potential deadlock situations. Fault tolerant compressionless routing (FCR) extends CR to support end to end fault tolerant delivery. Detailed routing algorithms, implementation complexity, and performance simulation results for CR and FCR are presented. These results show that the hardware for CR and FCR networks is modest. Further, CR and FCR networks can achieve superior performance to alternatives such as dimension order routing. Compressionless routing has several key advantages: deadlock free adaptive routing in toroidal networks with no virtual channels, simple router designs, order preserving message transmission, applicability to a wide variety of network topologies, and elimination of the need for buffer allocation messages. Fault tolerant compressionless routing has several additional advantages: data integrity in the presence of transient faults (nonstop fault tolerance), permanent fault tolerance, and elimination of the need for software buffering and retry for reliability. The advantages of CR and FCR not only simplify hardware support for adaptive routing and fault tolerance, they also can simplify software communication layers.

Selection of routing paths in data communications networks to satisfy multiple requirements

Abstract: Methods, systems and computer program products which identify network routing paths having a first performance characteristic less than a first specified limit and a second performance characteristic less than a second specified limit from a plurality of routing paths. These routing paths are identified by combining both the first performance characteristic and the second performance characteristic for one of the plurality of routing paths to provide a third performance characteristic which differs from both the first and the second performance characteristic and which operates as a proxy for the first and second performance characteristic. It is then determined if the third performance characteristic of the routing path is less than a third performance limit associated with the third performance characteristic.

On deadlocks in interconnection networks

Abstract: Deadlock avoidance-based and deadlock recovery-based routing algorithms have been proposed in recent years without full understanding of the likelihood and characteristics of actual deadlocks in interconnection networks. This work models the interrelationships between routing freedom, message blocking, correlated resource dependencies and deadlock formation. We empirically show that increasing routing freedom, as achieved by allowing unrestricted routing over multiple virtual channels, makes deadlocks highly improbable and reduces the likelihood of other types of correlated message blocking behavior that can degrade performance. Our results further substantiate that recovery-based routing algorithms have a higher potential performance advantage over deadlock avoidance-based routing algorithms which, inherently, allow less routing freedom.

On two-step routing for FPGAS

Abstract: We present results which show that a separate global and detailed routing strategy can be competitive with a combined routing process. Under restricted architectural assumptions, we compute a new lower bound for detailed routing and show that our detailed router typically requires no more than two extra routing tracks above this computed limit. Also, experimental results show that the Mapping Anomaly presented in [20], which suggests that separated routing may yield arbitrarily poor results in certain instances, is a concern only if nets are restricted to a single track domain. Finally, to motivate future work, we show the latest two-step routing results that we have achieved with the VPR global router and SEGA detailed router tools on the largest CBL benchmark circuits.

Post global routing crosstalk synthesis

Abstract: For the generation of a risk-free layout solution of a chip, crosstalk synthesis should be pursued at various stages in the routing process. This paper proposes a post global routing crosstalk optimization approach, which to our knowledge, is the first to estimate and reduce crosstalk risk at the global routing level. It consists of two parts: region-based crosstalk risk estimation and crosstalk risk reduction at the global routing level. In the first part, crosstalk risk graphs are first introduced for each routing region representing its current crosstalk situation. The crosstalk risk of each region, which indicates whether a risk-free routing solution of the region is possible, is then quantitatively defined and estimated using a graph-based approach. In the second part, the risk tolerance bound of each net is partitioned appropriately among its routing regions via integer linear programming for accurate (minimized) crosstalk risk estimation. If high risk regions still exist after bound partitioning, net ripping-up and rerouting is applied to reduce their crosstalk risks. At the end of the entire optimization process, a risk-free global routing solution is obtained together with partitions of nets' risk tolerance bounds which reflect the current crosstalk situation of the chip. These can greatly facilitate the generation of a risk-free final solution at later stages in the layout process. The proposed approach has been implemented and tested on CBL/NCSU benchmarks and the experimental results are very promising.

Improving the efficiency of adaptive routing in networks with irregular topology

Abstract: Networks of workstations are emerging as a cost-effective alternative to parallel computers. The interconnection between workstations usually relies on switch-based networks with irregular topologies. This irregularity makes routing and deadlock avoidance quite complicated. Current proposals avoid deadlock by removing cyclic dependencies between channels and therefore, many messages are routed along non-minimal paths, increasing latency and wasting resources. We propose a general methodology for the design of adaptive routing algorithms for networks with irregular topology that improves a previously proposed one by reducing the probability of routing over non-minimal paths. The resulting routing algorithms allow messages to follow minimal paths in most cases, reducing message latency and increasing network throughput. As an example of application, we propose an improved adaptive routing algorithm for Autonet.

Efficient Adaptive 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 topologies allow the wiring flexibility, scalability and incremental expansion capability required in this environment. The irregularity also makes routing and deadlock avoidance on such systems quite complicated. Current proposals avoid deadlock by removing cyclic dependencies between channels. As a consequence, many messages are routed following non-minimal paths, increasing latency and wasting resources. In this paper, we propose a general methodology for the design of adaptive routing algorithms for networks with irregular topology. These routing algorithms allow messages to follow minimal paths in most cases, reducing message latency and increasing network throughput. The methodology is based on the application of the theory of deadlock avoidance proposed in [14], which increases routing flexibility by allowing cyclic dependencies between channels. As an example of application, we propose an adaptive routing algorithm for Autonet. It 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. Preliminary evaluation results show that the new routing algorithm is able to increase throughput for random traffic by a factor of up to 2.8 with respect to the original algorithm, also reducing latency.

Efficient path determination in a routed network

Abstract: The topology of a computer network is represented, for each routing device in the network, as a tree structure with the root of the tree designating the particular routing device. Tree nodes represent LANs, while arcs connecting the nodes represent other routing devices. Thus, the number of first-level links to children off the root is equal to the number of LANs connected to the source routing device, and those first-level links point to nodes representing the LANs (or LAN segments) directly connected to the source routing device. As a result of this representation, each routing device can store a representation of the entire network adequate to facilitate routing, but with much less memory utilization than a list of addresses. Furthermore, because the network is represented at a more general level than that of individual station addresses, changes to the topology of the network can be readily introduced without the need for extensive (e.g., address by address) reconfiguration.

Deterministic many-to-many hot potato routing

Abstract: We consider algorithms for many-to-many hot potato routing. In hot potato (deflection) routing, a packet cannot be buffered, and is therefore always moving until it reaches its destination. We give optimal and nearly optimal deterministic algorithms for many-to-many packet routing in commonly occurring networks such as the hypercube, meshes, and tori of various dimensions and sizes, trees, and hypercubic networks such as the butterfly. All these algorithms are analyzed using a charging scheme that may be applicable to other algorithms as well. Moreover, all bounds hold in a dynamic setting in which packets can be injected at arbitrary times.

A method for routing of nets in an electronic device

Abstract: In laying out electronic devices on a substrate the routing of nets is important in minimizing conductor area and improving performance. A method for routing of nets in an electronic device which has a plurality of clusters is disclosed which separates the intra cluster routing and the channel routing between the clusters. For the intra cluster routing a topological graph is proposed to be used for mapping a subgraph which is representative of the nodes in a net belonging to a cluster to be routed.

Loop-free Internet routing using hierarchical routing trees

Abstract: We present a new hierarchical routing algorithm that combines the loop-free path-finding algorithm (LPA) with the area-based hierarchical routing scheme first proposed by McQuillan (1974) for distance-vector algorithms. The new algorithm, which we call the hierarchical information path-based routing (HIPR) agorithm, accommodates an arbitrary number of aggregation levels and can be viewed as a distributed version of Dijkstra's algorithm running over a hierarchical graph. The HIPR is verified to be loop-free and correct. Simulations are used to show that the HIPR is much more efficient than the OSPF in terms of speed, communication and processing overhead required to converge to correct routing tables. The HIPR constitutes the basis for future Internet routing protocols that are as simple as RIPv2, but with no looping and better performance than protocols based on link-states.

Fault-tolerant wormhole routing in mesh with overlapped solid fault regions

Abstract: A fault-tolerant wormhole routing algorithm on mesh-connected processors is proposed. The proposed algorithm is based on the solid fault model and allows the fault polygons to be overlapped. The algorithm utilizes the position of fault region relative to the current channel to route a message around overlapped fault polygons. A node deactivating algorithm to convert a non-solid fault region into a solid fault region is also proposed. The proposed routing algorithm uses four virtual channels and is deadlock- and livelock-free.

Performance of optimized routing in LEO intersatellite link networks

Abstract: An ATM based routing concept for LEO intersatellite link networks is proposed. The challenges arising from the complex time-variant ISL network topology are tackled by a discrete-time network model and routing procedure. The approach is based on the combination of a modified standard routing scheme and the ATM VPC concept. The routing scheme works completely off-line, i.e. prior to system operation. In a first step, a virtual topology is set up for all successive time intervals, providing instantaneous sets of alternative VPCs (paths) between all source-destination satellite pairs. In the second step, path sequences over a series of time intervals are chosen from that according to a certain optimization procedure. Two different optimization procedures are discussed in detail, and a numerical performance evaluation is presented for telephony service in an example ISL network (Iridium). The overall routing performance is evaluated in terms of remaining delay jitter due to inevitable path handover. The results show that optimized routing strategies are specifically capable of minimizing severe delay jitter, and thus in turn reduce the complexity of ATM based operation in a connection-oriented service environment.

A new hierarchical routing protocol for dynamic multihop wireless networks

Abstract: The routing techniques used in conventional packet radio networks are not suitable for dynamic multihop wireless networks because of their unique architecture. In this paper a new hierarchical multihop routing algorithm is introduced which balances the cost of location-update and path-finding operations by partitioning the terminals and mobile base stations to produce a virtual topology. Based on the virtual topology each network entity stores a fraction of the network topology information and maintains the routing efficiency. Finally, the performance of the hierarchical multihop routing algorithm is investigated through simulations.

Use of routing capability for fault-tolerant routing in hypercube multicomputers

Abstract: The concept of routing capability is proposed to assist fault-tolerant routing in hypercubes. Routing capability is defined with respect to the entire spectrum of distance. As a result, the amount of information that is useful for message routing is increased. An algorithm is presented to facilitate efficient fault-tolerant routing of messages. The algorithm routes a message in an attempt to minimize derouting. Furthermore, the concept of directed routing capability which contains more useful information for fault-tolerant routing is introduced. Simulation results demonstrate the usefulness of our approach.