Showing papers on "Equal-cost multi-path routing published in 2002"

Energy aware routing for low energy ad hoc sensor networks

Abstract: The recent interest in sensor networks has led to a number of routing schemes that use the limited resources available at sensor nodes more efficiently. These schemes typically try to find the minimum energy path to optimize energy usage at a node. In this paper we take the view that always using lowest energy paths may not be optimal from the point of view of network lifetime and long-term connectivity. To optimize these measures, we propose a new scheme called energy aware routing that uses sub-optimal paths occasionally to provide substantial gains. Simulation results are also presented that show increase in network lifetimes of up to 40% over comparable schemes like directed diffusion routing. Nodes also burn energy in a more equitable way across the network ensuring a more graceful degradation of service with time.

An overview of constraint-based path selection algorithms for QoS routing

Abstract: Constraint-based path selection aims at identifying a path that satisfies a set of quality of service (QoS) constraints. In general, this problem is known to be NP-complete, leading to the proposal of many heuristic algorithms. We provide an overview of these algorithms, focusing on restricted shortest path and multi-constrained path algorithms.

Algebra and algorithms for QoS path computation and hop-by-hop routing in the Internet

Abstract: Prompted by the advent of quality-of-service routing in the Internet, we investigate the properties that path weight functions must have so that hop-by-hop routing is possible and optimal paths can be computed with a generalization of E.W. Dijkstra's algorithm (see Numer. Math., vol.1, p.269-71, 1959). We define an algebra of weights which contains a binary operation, for the composition of link weights into path weights, and an order relation. Isotonicity is the key property of the algebra. It states that the order relation between the weights of any two paths is preserved if both of them are either prefixed or appended by a common, third, path. We show that isotonicity is both necessary and sufficient for a generalized Dijkstra's algorithm to yield optimal paths. Likewise, isotonicity is also both necessary and sufficient for hop-by-hop routing. However, without strict isotonicity, hop-by-hop routing based on optimal paths may produce routing loops. They are prevented if every node computes what we call lexicographic-optimal paths. These paths can be computed with an enhanced Dijkstra's algorithm that has the same complexity as the standard one. Our findings are extended to multipath routing as well. As special cases of the general approach, we conclude that shortest-widest paths can neither be computed with a generalized Dijkstra's algorithm nor can packets be routed hop-by-hop over those paths. In addition, loop-free hop-by-hop routing over widest and widest-shortest paths requires each node to compute lexicographic-optimal paths, in general.

Fixed-alternate routing and wavelength conversion in wavelength-routed optical networks

Abstract: Consider an optical network which employs wavelength-routing crossconnects that enable the establishment of wavelength-division-multiplexed (WDM) connections between node pairs. In such a network, when there is no wavelength conversion, a connection is constrained to be on the same wavelength channel along its route. Alternate routing can improve the blocking performance of such a network by providing multiple possible paths between node pairs. Wavelength conversion can also improve the blocking performance of such a network by allowing a connection to use different wavelengths along its route. This work proposes an approximate analytical model that incorporates alternate routing and sparse wavelength conversion. We perform simulation studies of the relationships between alternate routing and wavelength conversion on three representative network topologies. We demonstrate that alternate routing generally provides significant benefits, and that it is important to design alternate routes between node pairs in an optimized fashion to exploit the connectivity of the network topology. The empirical results also indicate that fixed-alternate routing with a small number of alternate routes asymptotically approaches adaptive routing in blocking performance.

Inferring link weights using end-to-end measurements

Abstract: We describe a novel constraint-based approach to approximate ISP link weights using only end-to-end measurements. Common routing protocols such as OSPF and IS-IS choose least-cost paths using link weights, so inferred weights provide a simple, concise, and useful model of intradomain routing. Our approach extends router-level ISP maps, which include only connectivity, with link weights that are consistent with routing. Our inferred weights agree well with observed routing: while our inferred weights fully characterize the set of shortest paths between 84--99% of the router-pairs, alternative models based on hop count and latency do so for only 47--81% of the pairs.

MRPC: maximizing network lifetime for reliable routing in wireless environments

Abstract: We propose MRPC, a new power-aware routing algorithm for energy-efficient routing that increases the operational lifetime of multi-hop wireless networks. In contrast to conventional power-aware algorithms, MRPC identifies the capacity of a node not just by its residual battery energy, but also by the expected energy spent in reliably forwarding a packet over a specific link. Such a formulation better captures scenarios where link transmission costs also depend on physical distances between nodes and the link error rates. Using a max-min formulation, MRPC selects the path that has the largest packet capacity at the 'critical' node (the one with the smallest residual packet transmission capacity). We also present CMRPC, a conditional variant of MRPC that switches from minimum energy routing to MRPC only when the packet forwarding capacity of nodes falls below a threshold. Simulation based studies have been used to quantify the performance gains of our algorithms.

Survivable lightpath routing: a new approach to the design of WDM-based networks

Abstract: Network restoration is often done at the electronic layer by rerouting traffic along a redundant path. With wavelength-division multiplexing (WDM) as the underlying physical layer, it is possible that both the primary and backup paths traverse the same physical links and would fail simultaneously in the event of a link failure. It is, therefore, critical that lightpaths are routed in such a way that a single link failure would not disconnect the network. We call such a routing survivable and develop algorithms for survivable routing of a logical topology. First, we show that the survivable routing problem is NP-complete. We then prove necessary and sufficient conditions for a routing to be survivable and use these conditions to formulate the problem as an integer linear program (ILP). Due to the excessive run-times of the ILP, we develop simple and effective relaxations for the ILP that significantly reduces the time required for finding survivable routings. We use our new formulation to route various logical topologies over a number of different physical topologies and show that this new approach offers a much greater degree of protection than alternative routing schemes such as shortest path routing and a greedy routing algorithm. Finally, we consider the special case of ring logical topologies for which we are able to find a significantly simplified formulation. We establish conditions on the physical topology for routing logical rings in a survivable manner.

Path set selection in mobile ad hoc networks

Abstract: Topological changes in mobile ad hoc networks frequently render routing paths unusable. Such recurrent path failures have detrimental effects on the network ability to support QoS-driven services. A promising technique for addressing this problem is to use multiple redundant paths between the source and the destination. However while multipath routing algorithms can tolerate network failures well their failure resilience only holds if the paths are selected judiciously. In particular the correlation between the failures of the paths in a redundant path set should be as small as possible. However selecting an optimal path set is an NP-complete problem. Heuristic solutions proposed in the literature are either too complex to be performed in real-time or too ineffective or both. This paper proposes a multipath routing algorithm called Disjoint Pathset Selection Protocol (DPSP) based on a novel heuristic that in nearly linear time on average picks a set of highly reliable paths. The convergence to a highly reliable path set is very fast and the protocol provides flexibility in path selection and routing algorithm. Furthermore DPSP is suitable for real-time execution with nearly no message exchange overhead and with minimal additional storage requirements. This paper presents evidence that multipath routing can mask a substantial number of failures in the network compared to single path routing protocols and that the selection of paths according to DPSP can be beneficial for mobile ad hoc networks since it dramatically reduces the rate of route discoveries.

Heuristic algorithms for multiconstrained quality-of-service routing

Abstract: Multiconstrained quality-of-service (QoS) routing deals with finding routes that satisfy multiple independent QoS constraints. This problem is NP-hard. In this paper, two heuristics, the limited granularity heuristic and the limited path heuristic, are investigated. Both heuristics extend the Bellman-Ford shortest path algorithm and solve general k-constrained QoS routing problems. Analytical and simulation studies are conducted to compare the time/space requirements of the heuristics and the effectiveness of the heuristics in finding paths that satisfy the QoS constraints. The major results of this paper are the following. For an N-nodes and E-edges network with k (a small constant) independent QoS constraints, the limited granularity heuristic must maintain a table of size O(|N|k- 1) in each node to be effective, which results in a time complexity of O (|N|K|E|); while the limited path heuristic can achieve very high performance by maintaining O (|N|2lg(|N|)) entries in each node. These results indicate that the limited path heuristic is relatively insensitive to the number of constraints and is superior to the limited granularity heuristic in solving k-constrained QoS routing problems when k > 3.

Content delivery network map generation using passive measurement data

Abstract: A routing method operative in a content delivery network (CDN) where the CDN includes a request routing mechanism for routing clients to subsets of edge servers within the CDN. According to the routing method, TCP connection data statistics are collected are edge servers located within a CDN region. The TCP connection data statistics are collected as connections are established between requesting clients and the CDN region and requests are serviced by those edge servers. Periodically, e.g., daily, the connection data statistics are provdied from the edge servers in a region back to the request routing mechanism. The TCP connection data statistics are then used by the request routing mechanism in subsequent routing decisions and, in particular, in the map generation processes. Thus, for example, the TCP connection data may be used to determine whether a given quality of service is being obtained by routing requesting clients to the CDN region. If not, the request routing mechanism generates a map that directs requesting clients away from the CDN region for a given time period or until the quality of service improves.

Information routing system and apparatus

Abstract: An information routing system and apparatus includes separate control and forwarding planes The control plane is split into box management control functions and routing control functions The box management control functions are isolated to a single processing card, while the routing control functions are distributed across multiple processing cards The routing table is also distributed across multiple processing cards The multiple processing cards are interconnected via a high-speed backplane bus for control plane traffic and by a fabric for forwarding plane traffic

Self Organized Terminode Routing

Abstract: We consider the problem of routing in a wide area mobile ad hoc network called Terminode Network. Routing in this network is designed with the following objectives. First, it should scale well in terms of the number of nodes and geographical coverage; second, routing should have scalable mechanisms that cope with the dynamicity in the network due to mobility; and third, nodes need to be highly collaborative and redundant, but, most of all, cannot use complex algorithms or protocols. Our routing scheme is a combination of two protocols called Terminode Local Routing (TLR) and Terminode Remote Routing (TRR). TLR is used to route packets to close destinations. TRR is used to route to remote destinations. The combination of TLR and TRR has the following features: (1) it is highly scalable because every node relies only on itself and a small number of other nodes for packet forwarding; (2) it acts and reacts well to the dynamicity of the network because as a rule multipath routing is considered; and (3) it can be implemented and run in very simple devices because the algorithms and protocols are very simple and based on high collaboration. We performed simulations of the TLR and TRR protocols using the GloMoSim simulator. The simulation results for a large, highly mobile ad hoc environment demonstrate benefits of the combination of TLR and TRR over an existing protocol that uses geographical information for packet forwarding.

System for and method of differentiated queuing in a routing system

Abstract: The invention relates to a method for routing Internet traffic. The method generally includes the steps of receiving a packet from multimedia network, allocating a message block header for the packet, wherein the header is used to hold behaviour aggregate values for internal router mapping, and queuing and routing the packet to a differentiated services network domain in a manner that ensures a specific QoS.

Detection and analysis of routing loops in packet traces

Abstract: Routing loops are caused by inconsistencies in routing state among a set of routers. They occur in perfectly engineered networks, and have a detrimental effect on performance. They impact end-to-end performance through increased packet loss and delay for packets caught in the loop, and through increased link utilization and corresponding delay and jitter for packets that traverse the link but are not caught in the loop.Using packet traces from a tier-1 ISP backbone, we first explain how routing loops manifest in packet traces. We characterize routing loops in terms of the packet types caught in the loop, the loop sizes, and the loop durations. Finally, we analyze the impact of routing loops on network performance in terms of loss and delay.

The extent of AS path inflation by routing policies

Abstract: A route in the Internet may take a longer AS (autonomous systems) path than the shortest AS path due to routing policies. We systematically analyze AS paths and quantify the extent to which routing policies inflate AS paths. The results show that AS path inflation in the Internet is more prevalent than expected. We first present the extent of AS path inflation observed from the route view routing tables. From an ISP, at least 55% of AS paths are inflated by at least one AS hop and AS paths can be inflated by as long as 6 AS hops. We then employ two typical routing policies to show the extent of AS path inflation for all AS pairs; we find that at least 45% of AS paths are inflated by at least one AS hop and AS paths can be inflated by as many as 9 AS hops. Quantifying AS path inflation in the Internet has important implications on the extent of routing policies and traffic engineering performed on the Internet, and on BGP (border gateway protocol) convergence speed.

Improving BGP convergence through consistency assertions

Abstract: This paper presents a new mechanism for improving the convergence properties of path vector routing algorithms, such as BGP. Using a route's path information, we develop two consistency assertions for path vector routing algorithms that are used to compare similar routes and identify infeasible routes. To apply these assertions in BGP, mechanisms to signal failure/policy withdrawal, and traffic engineering are provided. Our approach was implemented and deployed in a BGP testbed and evaluated using simulation. By identifying and ignoring the infeasible routes, we achieved substantial reduction in both BGP convergence time and the total number of intermediate route changes.

A constrained shortest-path energy-aware routing algorithm for wireless sensor networks

Abstract: While traditional routing protocols try to minimize the end-to-end delay or maximize the throughput, most energy-aware routing protocols for wireless sensor networks try to extend the life time of the network by minimizing the energy consumption sacrificing other performance metrics. We introduce a new energy-aware routing protocol that tries to minimize the energy consumption and, at the same time, maintain good end-to-end delay and throughput performance. The new algorithm is based on a constrained shortest-path algorithm. We compare the new algorithm with some traditional routing and energy-aware routing algorithms. The results show that the new algorithm performance is acceptable under all performance metrics and presents a performance balance between the traditional routing algorithms and the energy-aware routing algorithms. The constraint value can be chosen to achieve different performance objectives for different sensor network missions.

Power-aware routing based on the energy drain rate for mobile ad hoc networks

Abstract: Mobile ad hoc networks' (MANETs) inherent power limitation makes power-awareness a critical requirement for MANET protocols. We propose a new routing metric, the drain rate, which predicts the lifetime of a node as a function of current traffic conditions. We describe the minimum drain rate (MDR) mechanism which uses a combination of the drain rate with remaining battery capacity to establish routes. MDR can be employed by any existing MANET routing protocol to achieve a dual goal: extend both nodal battery life and connection lifetime. Using the ns-2 simulator and the dynamic source routing (DSR) protocol, we compared MDR to the minimum total transmission power routing (MTPR) scheme and the min-max battery cost routing (MM-BCR) scheme and proved that MDR is the best approach to achieve the dual goal.

Pattern routing: use and theory for increasing predictability and avoiding coupling

Abstract: Deep submicron effects, along with increasing interconnect densities, have increased the complexity of the routing problem. Whereas previously we could focus on minimizing wirelength, we must now consider a variety of objectives during routing. For example, an increased amount of timing restrictions means that we must minimize interconnect delay. But, interconnect delay is no longer simply related to wirelength. Coupling capacitance has become a dominant component of delay due to the shrinking of device sizes. Regardless, the most important objective is producing a routable circuit. Unfortunately, this often conflicts with minimizing interconnect delay as minimum delay routes create congested areas, for which an exact routing cannot be realized without violating design rules. In this work, we use the concept of pattern routing to develop algorithms that guide the router to a solution that minimizes interconnect delay - by considering both coupling and wirelength-without damaging the routability of the circuit. The paper is divided into two parts. The first part demonstrates that pattern routing can be used without affecting the routability of the circuit. We propose two schemes to choose a set of nets to pattern route. Using these schemes, we show that the routability is not hindered. The second part builds on the previous part by presenting a framework for coupling reduction using pattern routing. We develop theory and algorithms relating pattern routing and coupling. Additionally, we give suggestions on how to extend our theory and use our algorithms for both global and detailed routing.

Adaptive proportional routing: a localized QoS routing approach

Abstract: Most of the QoS routing schemes proposed so far require periodic exchange of QoS state information among routers, imposing both communication overhead on the network and processing overhead on core routers. Furthermore, stale QoS state information causes the performance of these QoS routing schemes to degrade drastically. In order to circumvent these problems, we focus on localized QoS routing schemes where the edge routers make routing decisions using only local information and thus reducing the overhead at core routers. We first describe virtual capacity based routing (vcr), a theoretical scheme based on the notion of virtual capacity of a route. We then propose proportional sticky routing, an easily realizable approximation of vcr and analyze its performance. We demonstrate through extensive simulations that adaptive proportional routing is indeed a viable alternative to the global QoS routing approach.

Heuristic techniques for accelerating hierarchical routing on road networks

Abstract: The route computation module is one of the most important functional blocks in a dynamic route guidance system. Although various algorithms exist for finding the shortest path, their performance tends to deteriorate as the network size increases. We present an efficient hierarchical routing algorithm that finds a near-optimal route and evaluate it on a large city road network. Solutions provided by the hierarchical routing algorithm are compared with the optimal solutions to analyze and quantify the loss of accuracy. We propose a novel yet simple heuristic to substantially improve the performance of the hierarchical routing algorithm with acceptable loss of accuracy. A network pruning technique has been incorporated into the algorithm to reduce the search space and the correctness of the results is evaluated. The improved hierarchical routing algorithm that incorporates the heuristic techniques has been found to be over 50 times faster than a typical shortest path algorithm.

Rapidly switching all-optical packet routing system with optical-label swapping incorporating tunable wavelength conversion and a uniform-loss cyclic frequency AWGR

Abstract: This letter discusses an experimental demonstration of a rapidly switching all-optical packet routing system with optical-label switching and all-optical label-swapping capabilities. The optical routing system optically extracts the subcarrier optical-label content, compares it against the forwarding table, makes packet forwarding and label-swapping decisions, and forward the packet to the desired output with a newly updated subcarrier optical label. The packet switching fabric included a combination of rapidly tunable wavelength conversion and a uniform-loss cyclic frequency 8/spl times/8 arrayed waveguide grating router. The packet routing system achieved 600-ps switching time and 250-ns forwarding decision time. Accumulated packet bit-error-rate measurements confirm the successful error-free packet routing with all-optical label-swapping.

On characterizing BGP routing table growth

Abstract: BGP routing table sizes have increased by an order of magnitude over the last six years. This dramatic growth can decrease packet forwarding speed and demand more router memory space. We explore the extent that various factors contribute to the routing table size and characterize the growth of each contribution. We begin with a measurement study using the routing tables of an Oregon route views server to determine the contributions of multi-homing, load balancing, address fragmentation, and failure-to-aggregate to routing table size. Address fragmentation makes the greatest contribution and it is three times those of multihoming or load balancing. The contribution of failure-to-aggregate is the least. Although multihoming and load balancing contribute less to routing table size than address fragmentation, we observe that their contributions grow faster than the routing table does and that load balancing has surpassed multihoming, becoming the fastest growing contributor. Moreover, we find that both load balancing and multihoming contribute to routing table growth by introducing more prefixes of length between 17 and 25, which are the fastest growing prefixes. Next, we examine the growth routable IP addresses, and conclude that their growth is much slower than that of routing table size. Lastly, we demonstrate that our findings based on views derived from the Oregon server are accurate through an evaluation using 15 additional routing tables collected from different locations in the Internet.

System and method for managing interconnect carrier routing

Abstract: A system and method for managing a carrier's interconnect traffic across a telecommunications network, the method involving receiving cost and routing rules from the carrier, gathering performance data corresponding to the interconnect traffic, applying the cost and routing rules to the performance data to determine a first impact on the interconnect traffic, receiving superseding routing rules from the carrier, automatically calculating proposed changes in network routing based on the superseding routing rules and the first impact, and presenting the proposed changes to the carrier.

Routing system and method for synchronizing a routing system with peers after failover

Abstract: A routing system provides for transparent routing system failover by checkpointing route prefixes during normal operation by maintaining a route prefix table. After failure of a primary routing processor, routing with peer routing systems is synchronized through the use of this prefix table. The prefix table is managed by the primary routing processor and is accessible by a backup routing processor at least after failure of the primary routing processor. Upon the detection of a failure, a backup routing processor solicits routes from peer routing systems in response to the failure and generates a backup routing database from the routes received from peer routing systems. The backup routing processor also compares prefixes of routes in the backup routing database with prefixes in the prefix table, and sends route withdraw messages to the peer routing systems for routes having prefixes listed in the prefix table and not identified in the backup routing database.

A new bandwidth guaranteed routing algorithm for MPLS traffic engineering

Abstract: In this paper, we present a new online algorithm for dynamically routing bandwidth guaranteed label switched paths (LSPs). LSP set-up requests are represented in terms of a pair of ingress and egress routers as well as its bandwidth requirement, and arrive one by one. There is no a priori knowledge regarding future LSP set-up requests and their characteristics. Our proposed algorithm considers not only the importance of critical links, but also the degree of their importance to routing possible future LSP set-up requests by characterizing their normalized bandwidth contribution to routing future LSP demands. Moreover, link residual bandwidth information, i.e., the link's capability of routing future LSPs, is also incorporated. Simulation results show that our proposed algorithm performs better than the best known bandwidth guaranteed routing algorithm, the minimum interference routing algorithm, in terms of LSP rejection rate under both static and dynamic LSP set-up request arrivals.

Layered shortest path (LASH) routing in irregular system area networks

Abstract: In recent years we have seen a growing interest in irregular network topologies for cluster interconnects. One problem related to such topologies is that the combination of shortest path and deadlock free routing is difficult. As a result of this the existing solutions for routing in irregular networks either guarantee shortest paths relative to some constraint (like up*/down*), or have to resort to deadlock recovery through non-minimal escape channels. In this paper we propose a method that guarantees shortest path routing and in-order delivery, and that uses virtual channels for deadlock avoidance. We present a theoretical upper bound on the number of virtual channels needed, and through extensive empirical testing we demonstrate that the actual number of virtual channels is very low even for large networks.

DORA: Efficient Routing for MPLS Traffic Engineering

Abstract: This paper introduces DORA, a dynamic online routing algorithm for construction of bandwidth guaranteed paths in MPLS-enabled networks. The main objective of DORA is to place paths with reserved bandwidth evenly across the network in order to allow more future paths to be accepted into the network and to balance the traffic load. During path computation, the key operation in DORA is to avoid routing over links that (1) have high potential to be part of any other path, and (2) have low residual bandwidth available. Our simulation results based on unsuccessful path-setup ratio and successful path-reroutes upon link failure, show that DORA offers better performance than some sophisticated algorithms, while at the same time being less computationally expensive.

Worst-case Traffic for Oblivious Routing Functions

Abstract: This paper presents an algorithm to find a worst-case trafficpattern for any oblivious routing algorithm on an arbitrary interconnectionnetwork topology. The linearity of channel loading offered by obliviousrouting algorithms enables the problem to be mapped to a bipartitemaximum-weight matching, which can be solved in polynomial time forrouting functions with a polynomial number of paths. Finding exact worstcaseperformance was previously intractable, and we demonstrate an examplecase where traditional characterization techniques overestimate thethroughput of a particular routing algorithm by 47%.