Showing papers on "Equal-cost multi-path routing published in 1999"

Distributed quality-of-service routing in ad hoc networks

Abstract: In an ad hoc network, all communication is done over wireless media, typically by radio through the air, without the help of wired base stations. Since direct communication is allowed only between adjacent nodes, distant nodes communicate over multiple hops. The quality-of-service (QoS) routing in an ad hoc network is difficult because the network topology may change constantly, and the available state information for routing is inherently imprecise. In this paper, we propose a distributed QoS routing scheme that selects a network path with sufficient resources to satisfy a certain delay (or bandwidth) requirement in a dynamic multihop mobile environment. The proposed algorithms work with imprecise state information. Multiple paths are searched in parallel to find the most qualified one. Fault-tolerance techniques are brought in for the maintenance of the routing paths when the nodes move, join, or leave the network. Our algorithms consider not only the QoS requirement, but also the cost optimality of the routing path to improve the overall network performance. Extensive simulations show that high call admission ratio and low-cost paths are achieved with modest routing overhead. The algorithms can tolerate a high degree of information imprecision.

Scalable routing strategies for ad hoc wireless networks

Abstract: We consider a large population of mobile stations that are interconnected by a multihop wireless network. The applications of this wireless infrastructure range from ad hoc networking (e.g., collaborative, distributed computing) to disaster recovery (e.g., fire, flood, earthquake), law enforcement (e.g., crowd control, search-and-rescue), and military (automated battlefield). Key characteristics of this system are the large number of users, their mobility, and the need to operate without the support of a fixed (wired or wireless) infrastructure. The last feature sets this system apart from existing cellular systems and in fact makes its design much more challenging. In this environment, we investigate routing strategies that scale well to large populations and can handle mobility. In addition, we address the need to support multimedia communications, with low latency requirements for interactive traffic and quality-of-service (QoS) support for real-time streams (voice/video). In the wireless routing area, several schemes have already been proposed and implemented (e.g., hierarchical routing, on-demand routing, etc.). We introduce two new schemes-fisheye state routing (FSR) and hierarchical state routing (HSR)-which offer some competitive advantages over the existing schemes. We compare the performance of existing and proposed schemes via simulation.

CEDAR: a core-extraction distributed ad hoc routing algorithm

Abstract: We present CEDAR, a core-extraction distributed ad hoc routing algorithm for quality-of-service (QoS) routing in ad hoc network environments, CEDAR has three key components: (a) the establishment and maintenance of a self-organizing routing infrastructure called the core for performing route computations; (b) the propagation of the link-state of high bandwidth and stable links in the core through increase/decrease waves; and (c) a QoS-route computation algorithm that is executed at the core nodes using only locally available state. The performance evaluations show that CEDAR is a robust and adaptive QoS routing algorithm that reacts quickly and effectively to the dynamics of the network while still approximating the performance of link-state routing for stable networks.

On-demand multipath routing for mobile ad hoc networks

Abstract: Mobile ad hoc networks are characterized by multi-hop wireless links, absence of any cellular infrastructure, and frequent host mobility. Design of efficient routing protocols in such networks is a challenging issue. A class of routing protocols called on-demand protocols has recently attracted attention because of their low routing overhead. The on-demand protocols depend on query floods to discover routes whenever a new route is needed. Such floods take up a substantial portion of network bandwidth. We focus on a particular on-demand protocol, called dynamic source routing, and show how intelligent use of multipath techniques can reduce the frequency of query floods. We develop an analytic modeling framework to determine the relative frequency of query floods for various techniques. Results show that while multipath routing is significantly better than single path routing, the performance advantage is small beyond a few paths and for long path lengths. It also shows that providing all intermediate nodes in the primary (shortest) route with alternative paths has a significantly better performance than providing only the source with alternate paths.

The end-to-end effects of Internet path selection

Abstract: The path taken by a packet traveling across the Internet depends on a large number of factors, including routing protocols and per-network routing policies. The impact of these factors on the end-to-end performance experienced by users is poorly understood. In this paper, we conduct a measurement-based study comparing the performance seen using the "default" path taken in the Internet with the potential performance available using some alternate path. Our study uses five distinct datasets containing measurements of "path quality", such as round-trip time, loss rate, and bandwidth, taken between pairs of geographically diverse Internet hosts. We construct the set of potential alternate paths by composing these measurements to form new synthetic paths. We find that in 30-80% of the cases, there is an alternate path with significantly superior quality. We argue that the overall result is robust and we explore two hypotheses for explaining it.

A wireless hierarchical routing protocol with group mobility

Abstract: In this paper we present a hierarchical routing protocol in a large wireless, mobile network such as found in the automated battlefield or in extensive disaster recovery operations. Conventional routing does not scale well to network size. Likewise, conventional hierarchical routing cannot handle mobility efficiently. We propose a novel soft state wireless hierarchical routing protocol-Hierarchical State Routing (HSR). We distinguish between the "physical" routing hierarchy (dictated by geographical relationships between nodes) and "logical" hierarchy of subnets in which the members move as a group (e.g., company, brigade, battalion in the battlefield). HSR keeps track of logical subnet movements using home agent concepts akin to Mobile IP. A group mobility model is introduced and the performance of the HSR is evaluated through a detailed wireless simulation model.

A simple approximation to minimum-delay routing

Abstract: 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, minimum-delay 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 introduce the first routing algorithm based on link-state information that provides multiple paths of unequal cost to each destination that are loop-free at every instant. We show through simulations that the delays obtained in our framework are comparable to those obtained using the Gallager's minimum-delay routing. Also, we show that our framework renders far smaller delays and makes better use of resources than traditional single-path routing.

MCEDAR: multicast core-extraction distributed ad hoc routing

Abstract: In this paper, we present the MCEDAR (multicast core extraction distributed ad hoc routing) multicast routing algorithm for ad hoc networks. MCEDAR is an extension to the CEDAR architecture and provides the robustness of mesh based routing protocols and the approximates the efficiency of tree based forwarding protocols. It decouples the control infrastructure from the actual data forwarding infrastructure. The decoupling allows for a very minimalistic and low overhead control infrastructure while still enabling very efficient data forwarding.

Load-sensitive routing of long-lived IP flows

Abstract: Internet service providers face a daunting challenge in provisioning network resources, due to the rapid growth of the Internet and wide fluctuations in the underlying traffic patterns. The ability of dynamic routing to circumvent congested links and improve application performance makes it a valuable traffic engineering tool. However, deployment of load-sensitive routing is hampered by the overheads imposed by link-state update propagation, path selection, and signaling. Under reasonable protocol and computational overheads, traditional approaches to load-sensitive routing of IP traffic are ineffective, and can introduce significant route flapping, since paths are selected based on out-of-date link-state information. Although stability is improved by performing load-sensitive routing at the flow level, flapping still occurs, because most IP flows have a short duration relative to the desired frequency of link-state updates. To address the efficiency and stability challenges of load-sensitive routing, we introduce a new hybrid approach that performs dynamic routing of long-lived flows, while forwarding short-lived flows on static preprovisioned paths. By relating the detection of long-lived flows to the timescale of link-state update messages in the routing protocol, route stability is considerably improved. Through simulation experiments using a one-week ISP packet trace, we show that our hybrid approach significantly outperforms traditional static and dynamic routing schemes, by reacting to fluctuations in network load without introducing route flapping.

Dynamic wavelength routing using congestion and neighborhood information

Abstract: We present two dynamic routing algorithms based on path and neighborhood link congestion in all-optical networks. In such networks, a connection request encounters higher blocking probability than in circuit-switched networks because of the wavelength-continuity constraint. Much research has focused on the shortest-path routing and alternate shortest-path routing. We consider fixed-paths least-congestion (FPLC) routing in which the shortest path may not be preferred to use. We then extend the algorithm to develop a new routing method: dynamic routing using neighborhood information. It is shown by using both analysis and simulation methods that FPLC routing with the first-fit wavelength-assignment method performs much better than the alternate routing method in mesh-torus networks (regular topology) and in the NSFnet T1 backbone network (irregular topology). Routing using neighborhood information also achieves good performance when compared to alternate shortest-path routing.

Origins of Internet routing instability

Abstract: This paper examines the network routing messages exchanged between core Internet backbone routers. 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 led to the loss of internal connectivity in wide-area, national networks. In an earlier study of inter-domain routing, we described widespread, significant pathological behaviour in the routing information exchanged between backbone service providers at the major US public Internet exchange points. These pathologies included several orders of magnitude more routing updates in the Internet core than anticipated, large numbers of duplicate routing messages, and unexpected frequency components between routing instability events. The work described in this paper extends our earlier analysis by identifying the origins of several of these observed pathological Internet routing behaviour. We show that as a result of specific router vendor software changes suggested by our earlier analysis, the volume of Internet routing updates has decreased by an order of magnitude. We also describe additional router software changes that can decrease the volume of routing updates exchanged in the Internet core by an additional 30 percent or more. We conclude with a discussion of trends in the evolution of Internet architecture and policy that may lead to a rise in Internet routing instability.

Implementation and performance measurements of QoS routing extensions to OSPF

Abstract: We discuss an implementation of QoS routing extensions to the open shortest path first (OSPF) routing protocol and evaluate its performance over a wide range of operating conditions. Our evaluations are aimed at assessing the cost and feasibility of QoS routing in IP networks. The results provide insight into the respective weights of the two major components of QoS routing costs, processing cost and protocol overhead and establish strong empirical evidence that the cost of QoS routing is well within the limits of modern technology and can be justified by the performance improvements.

A performance model for Duato's fully adaptive routing algorithm in k-ary n-cubes

Abstract: Analytical models of deterministic routing in wormhole-routed k-ary n-cubes have widely been reported in the literature. Although many fully adaptive routing algorithms have been proposed to overcome the performance limitations of deterministic routing, there have been hardly any studies that describe analytical models for these algorithms. This paper proposes a new analytical model for obtaining latency measures in high-radix k-ary n-cubes with fully adaptive routing, based on Duato's algorithm (1998). The validity of the model is demonstrated by comparing analytical results with those obtained through simulation experiments.

Parallelization of the Vehicle Routing Problem with Time Windows

Abstract: Parallelization of the Vehicle Routing Problem with Time Windows This dissertation presents a number of algorithms for solving the Vehicle Routing Problem with Time Windows (VRPTW). The VRPTW is a generalization of the well known capacity constrained Vehicle Routing Problem (VRP). In the VRP a fleet of vehicles based at a central depot must service a set of customers. In the VRPTW each customer has a time window. Service of a customer must begin within the interval given by the time window. The objective is to minimize some aspect of operating costs (e.g. total distance traveled, number of vehicles needed or a combination of parameters). Since the late 80's and the beginning of the 90's optimal methods for the VRPTW have appeared in the literature. Methods have basicly been based on three approaches: dynamic programming, Lagrange relaxation and column generation (Dantzig-Wolfe). The most successful approaches rely on column generation. Good results have also been obtained using Lagrange relaxation. This dissertation is divided into three parts. First the theoretical framework is described. Thereafter a number of techniques to improve the performance of the column-generation framework are proposed and analyzed. Finally a parallel algorithm based on the sequential algorithm developed in the previous part of the dissertation is developed and analyzed.

Quality-of-service routing using maximally disjoint paths

Abstract: We apply and evaluate a new efficient algorithm for finding maximally link disjoint pairs of paths in a network. We apply this algorithm for QoS routing in connection-oriented networks that support calls with multiple QoS requirements. Our algorithm (called MADSWIP) is applied for precomputing paths in advance of call arrivals. Through simulations, we compare our QoS routing method to another method that is typical of what a switch vendor might implement today. We then examine the performance of three different policies for selecting a path among multiple potential paths. We also study the effects of decreasing the density of a network topology. We study two styles of topologies: commercial-style and random topologies. We demonstrate that precomputing paths that have minimal overlap is more important than precomputing paths that explicitly address all QoS metrics in a network. We also show that load balancing policies outperform call packing policies in networks that support diverse applications.

A position-based multi-zone routing protocol for wide area mobile ad-hoc networks

Abstract: We propose a proactive, position-based routing protocol that provides an alternative, simplified way of localizing routing information overhead, without having to resort to complex, multiple-tier hierarchical routing organization schemes. This is achieved by integrating the functions of routing and mobility management via the use of geographic position, and the generalization of the routing zone concept. The proposed protocol controls routing overhead generation and propagation by making the overhead generation rate and propagation distance directly proportional to the amount of change in a node's geographic position. In our protocol, a set of geographic routing zones is defined for each node, where the purpose of the ith routing zone is to contain propagation of position updates advertising position differentials equal to the radius of the (i-l)th routing zone. Finally, we show through simulation that the proposed routing protocol is a bandwidth-efficient routing mechanism that can be applied across large scale networks.

A fast IP routing lookup scheme for gigabit switching routers

Abstract: One of the key design issues for the new generation IP routers is the route lookup mechanism. For each incoming IP packet, the IP routing requires to perform a longest prefix matching on the address lookup in order to determine the packet's next hop. This paper presents a fast route lookup mechanism that only needs tiny SRAM and can be implemented in a pipelined skill in hardware. Based on the proposed scheme, the forwarding table is tiny enough to fit in SRAM with very low cost. For example, a large routing table with 40,000 routing entries can be compacted to a forwarding table of 450-470 Kbytes. In the worst case, the number of memory accesses for a lookup is three. When implemented in a pipeline skill in hardware, the proposed mechanism can achieve one routing lookup every memory access. With current 10 ns SRAM, this mechanism furnishes approximately 100 million routing lookups per second. This is much faster than any current commercially available routing lookup schemes.

Approach for routing an integrated circuit

Abstract: A computer-implemented approach for routing an integrated circuit using non-orthogonal routing is accomplished during two phases: a global routing phase and a detailed routing phase. During global routing, routing indicators, in the form of hint polygons, are added to the integrated circuit layout and strategy lists, that include bias directions and straying limits, are generated for the new wires to be added. The hint polygons and strategy lists are used during detailed routing to aid in placing the new wires. If obstacle conflicts or insufficient space problems prevent the detailed routing of a new wire, then an obstacle resolution portion of global routing is used to resolve the obstacle conflict and/or provide additional space in the integrated circuit layout to route the new wires. Obstacle resolution includes, without limitation, moving or changing layout geometry, changing or add hint polygons, changing the routing strategy by changing the bias direction and/or adjusting straying limits, inserting one or more layer changes, instructing the detailed router to backup and insert a bend, ripping-up and rerouting one or more wires, or routing the wire from the destination connection point. Also, a tight routing approach may be employed to accommodate constructing routing paths in tight layout areas. Object specific design rule checks are employed to increase routing flexibility optimize routing performance. “On-the-fly” design rule checks are performed on portions of routing paths as the routing paths are being constructed.

Communication node apparatus with routing tables in cache memories

Abstract: In a communication node apparatus comprising a plurality of line interfaces each having a cache memory with a sub routing table formed therein, and a route management unit having a main routing table, each of the line interfaces is provided with a function of detecting a disconnection flag included in a received packet and deleting an unnecessary routing information entry from the sub routing table, and a function of registering a routing information entry as a high priority entry if a connection establishment flag is set to a received packet when the routing information entry is downloaded from the main routing table to the sub routing table upon reception of the packet.

Routing with service level guarantees between ingress-egress points in a packet network

Abstract: A packet network of interconnected nodes employs a method of routing with service level guarantees to determine a path through the network for a requested label-switched path (LSP). Each of the nodes includes one or more routers that forward packets based on a forwarding table constructed from paths determined in accordance with the method of routing with service level guarantees. The method of routing with service level guarantees determines the path of the requested LSP based on the effect that routing those packets of the requested LSP may have on current and/or future demands on the capacity of network nodes for currently provisioned LSPs. Such method of routing with service level guarantees may not necessarily route packets of a requested LSP along the shortest path, or minimum number of hops, through the network. Given the packet network and LSP request, a linear programming system may be defined by a set of linear programming equations for a non-split demand case. The linear programming system is based on the network topology, the values of the ingress-egress point pair o and t and demand bd of the LSP request, and the total maxflow values of the existing ingress-egress point pair for currently provisioned LSPs. To estimate the solution for the linear programming system, a subnetwork is formed using link weights and links removed that cannot support the requested demand. Link weights are calculated based on the critical links of a pseudo-network in which increased maximum flow along existing paths between ingress-egress point pairs is maintained. A shortest path routing algorithm may then be employed to generate a path, if available, for the LSP request using the subnetwork with the calculated link weights.

Hop-by-hop routing with node-dependent topology information

Abstract: This paper is focused on the problem of hop-by-hop routing in a network where different nodes have different views of the network topology. In particular, each node may be aware of just a subset of the network links, perceiving the rest as if their cost was infinite. We formalize the idea of node's individual view of the network with the concept of visibility sets and introduce a routing approach based on the notion of a feasible path, i.e., such path in the node's visibility set that satisfies certain specified restrictions. It is shown that, in a network with general visibility sets, forwarding the packet along an optimal feasible path is necessary and sufficient to guarantee its eventual delivery to destination without being dropped or routed to the same node twice. Based on the proposed approach, we derive the precise routing policy and formulate an efficient algorithm to search for a family of one-to-all optimal feasible paths in a network with embedded visibility sets. We then proceed to prove the correctness of the algorithm. The new routing method provides for execution of multiple dynamic routing protocols, possibly overlaying each other in the same address space, within a network with common kinds of metrics of arbitrary complexity. It solves the problem of interoperability when new metrics or novel link properties are being introduced and eliminates the necessity to run different protocols and protocol versions within disjoint routing domains.

An implicit connection graph maze routing algorithm for ECO routing

Abstract: ECO routing is a very important design capability in advanced IC, MCM and PCB designs when additional routings need to be made at the latter stage of the physical design. ECO is difficult in two aspects: first, there are a large number of existing interconnects which become obstacles in the region. A hierarchical approach is not applicable in this situation, and we need to search a large, congested region thoroughly. Second, advances in circuit designs require variable width and variable spacing on interconnects. Thus, a gridless routing algorithm is needed. In this paper, we propose to use an implicit representation of a non-uniform grid graph for gridless maze routing algorithm. A novel slit-tree plus interval-tree data structure is developed, combined with a cache structure, to support efficient queries into the connection graph. Our experiments show that this data structure is very small in memory usage while very fast in answering maze expansion related queries. This make the framework very useful in the ECO type of routing.

Power-aware routing in wireless packet networks

Abstract: A key characteristic of personal area networks (PANs) is the premium placed on reducing the power consumption of device computation and communication. In such an environment some devices may be more capable of communicating with others simply because of their power capability (i.e., reserve). We propose a "power-aware" routing protocol capable of routing packets in PANs based on power related optimization and device behavior criteria. Our proposal differs from previous work on power consumption in wireless packet networks which typically aim to reduce the overall device usage and energy consumption.

Constraint-based routing between ingress-egress points in a packet network

Abstract: A packet network of interconnected nodes employs a constraint-based routing method to determine a path through the network for a requested label-switched path (LSP). Each of the nodes includes one or more routers that forward packets based on a forwarding table constructed from paths determined in accordance with the constraint-based routing method. The constraint-based method determines the path of the requested LSP based on the effect that routing those packets of the requested LSP may have on current and/or future demands on the capacity of network nodes for currently provisioned LSPs. Such constraint-based routing method may not necessarily route packets of a requested LSP along the shortest path, or minimum number of hops, through the network. Given the packet network and LSP request, a linear programming system is defined by a set of linear programming equations. The linear programming system is based on the network topology, the values of the ingress-egress point pair o and t and demand bd of the LSP request, and the total maxflow values of the existing ingress-egress point pair for currently provisioned LSPs. The solution is estimated for a linear programming system of either split demand, non-split demand, or batch demand implementations for routing packets of the LSP. The constraint-based routing method may solve the linear programming system using common linear programming techniques.

Method and apparatus for layout-constrained global routing

Abstract: A global router uses an algorithm for controlling routing based upon rough topologies. In one embodiment a set of regions and layers is specified over which the routing must occur. Tunnels can be defined outside of which routing cannot occur. Topologies of previous iterations are considered. Restrictions on the amount of deviation between successive iterations can be specified. As a result, successive iterations of the global router do not cause large changes in the timing delays of circuits. In addition, partial tunnels can be stretched to accommodate nearby nets. Also described are an integrated circuit that is produced using the layout-constrained global routing algorithm and a computer-readable medium storing computer-executable instructions and at least one data structure for implementing the algorithm.

A gridless multilayer router for standard cell circuits using CTM cells

Abstract: We present a gridless multilayer router suitable for standard cell circuits using central terminal model (CTM) cells. A CTM cell has pins in the middle which split the over-the-cell (OTC) routing region into top and bottom parts. Nets are routed in both the channel (if needed) and OTC by using a channel router. Our router uses a combined constraint graph and tile expansion algorithm. We report the first maze router to take advantage of a graph based algorithm to solve the net ordering problem. Unlike a laggard pure maze router, it has the time efficiency of a fast graph based algorithm and the better results of a maze routing algorithm. This is also the first report of the use of a tile expansion maze router for the variable height routing problem. By variable height routing we mean that a single execution of the routing algorithm will result in a completely routed solution. The only thing that is not determined a priori is the height or number of tracks needed. Our router achieves channelless solutions for the Primary1 circuit by routing over the cell in three layers. It also generates equal or better results compared to the best of the previous channel routers for all the examples we have tried. In fact, Sockeye is the first router to achieve density solutions for the r1, r3, and r4 examples for two layers and for the r3 example for three layers.

Flexible and efficient routing based on progressive deadlock recovery

Abstract: The development of fully adaptive, cut-through (wormhole) networks is important for achieving high performance in communication-critical parallel processor systems. Increased flexibility in routing allows network bandwidth to be used efficiently, but also creates more opportunity for cyclic resource dependencies to form which can cause deadlock. If not guarded against, deadlocks in routing make packets block in the network indefinitely and, eventually, could result in the entire network coming to a complete standstill. The paper presents a simple, flexible, and efficient routing approach for multicomputer interconnection networks which is based on progressive deadlock recovery as proposed to deadlock avoidance or regressive deadlock recovery. Performance is optimized by allowing the maximum routing freedom provided by network resources to be exploited. True fully adaptive routing is supported in which all physical and virtual channels at each node in the network are available to packets without regard for deadlocks. Deadlock cycles, upon forming, are efficiently broken in finite time by progressively routing one of the blocked packets through a connected, deadlock-free recovery path. This routing approach enables the design of high-throughput networks that provide excellent performance. Simulations indicate that progressive deadlock recovery routing can improve throughput by as much as 45 percent and 25 percent over leading deadlock avoidance-based and regressive recovery-based routing schemes, respectively.

Method and system for performing capacitance estimations on an integrated circuit design routed by a global routing tool

Abstract: A method for performing capacitance estimations on an integrated circuit design routed by a global routing tool is disclosed. Routing areas and pin locations of a net within an integrated circuit design are initially obtained from a global routing tool. Common boundaries among the routing areas are then defined. Before the performance of a detailed routing step, congestion information furnished by the global routing tool is utilized to perform probabilistic capacitance calculations for an interconnect that can be routed within the routing areas via the defined common boundaries to connect the pin locations.