Routing Loops Research Articles

Distributed algorithm for node localization in wireless ad-hoc networks

We present a distributed algorithm for node localization based on the Gauss-Newton method. In this algorithm, each node updates its own location estimate using the pairwise distance measurements and the local information it receives from the neighboring nodes. Once the location estimate is updated, the sensor node broadcasts the updated estimate to all the neighboring nodes. A distributed and scalable local scheduling algorithm for updating nodes in the network is presented to avoid the use of the global coordinator or a routing loop. We analytically show that the proposed distributed algorithm converges under certain practical assumptions of the network. The performance of the algorithm is evaluated using both simulation and experimental results. Quantitative comparisons among different distributed algorithms are also presented.

A Routing Scheme for the IEEE-802.15.4-Enabled Wireless Sensor Networks

A wireless sensor network (WSN) has features that fit into several classes of wireless networks (e.g., mesh, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ad hoc</i> , and mobile ad hoc networks) and, at the same time, features that are unique to it. These exceptional characteristics place many demands on the WSN routing protocol. For instance, the routing protocol must assure uniform dissipation of energy across the network, quickly converge irrespective of the network node density, and be flexible in terms of the routing framework and the route computation metric. All of the aforementioned conditions must be accomplished in an energy-efficient manner. Although several routing protocols have been proposed for WSNs, most approaches are usually focused on energy-efficient operations. The validity of this case is undeniable; however, one crucial element is generally assumed or ignored i.e., how one can prevent routing loops in the network. In addition to achieving the aforementioned routing objectives, in this paper, we go one step further by expressly defining and thoroughly evaluating mechanisms for loop prevention and minimization. Our proposed routing scheme leverages the services that were offered by the IEEE 802.15.4 specification to satisfy the requirements of a WSN routing protocol.

Solution to the problem of ant being stuck by ant colony routing algorithm

Many ant colony routing (ACR) algorithms have been presented in recent years, but few have studied the problem that ants will get stuck with probability in any terminal host when they are searching paths to route packets around a network. The problem has to be faced when designing and implementing the ACR algorithm. This article analyzes in detail the differences between the ACR and the ant colony optimization (ACO). Besides, particular restrictions on the ACR are pointed out and the three causes of ant being-stuck problem are obtained. Furthermore, this article proposes a new ant searching mechanism through dual path-checking and online routing loop removing by every intermediate node an ant visited and the destination host respectively, to solve the problem of ant being stuck and routing loop simultaneously. The result of numerical simulation is abstracted from one real network. Compared with existing two typical ACR algorithms, it shows that the proposed algorithm can settle the problem of ant being stuck and achieve more effective searching outcome for optimization path.

Looping in OLSRv2 in Mobile Ad-Hoc Networks, Loop Suppession and Loop Correction

Transient routing loops have been observed to form in Mobile Ad-hoc Networks running the OLSRv2 proactive link-state routing protocol. The packets falling into loops impact the surrounding network thus degrading throughput even though only a small proportion of the traffic may enter these loops and only for a short time. This becomes significantly more evident when Link Layer Notification is used to catch broken links, inadvertently leading to an increase in the number of loops. Two methods of Loop Detection are introduced and are used to trigger either Loop Suppression by selectively and preemptively discarding the looping packets that are unlikely to reach their destination, or Loop Correction by the notification of the routing protocol to cut the link over which the packet is looping. The newly introduced Loop Suppression and Loop Correction techniques used with Link Layer Notification are shown to significantly increase network performance over plain OLSRv2 and OLSRv2 with Link Layer Notification.

A Nonlinear Approach to Robust Routing Based on Reinforcement Learning with State Space Compression and Adaptive Basis Construction

A robust routing algorithm was developed based on reinforcement learning that uses (1) reward-weighted principal component analysis, which compresses the state space of a network with a large number of nodes and eliminates the adverse effects of various types of attacks or disturbance noises, (2) activity-oriented index allocation, which adaptively constructs a basis that is used for approximating routing probabilities, and (3) newly developed control space compression based on a potential model that reduces the control space for routing probabilities. This algorithm takes all the network states into account and reduces the adverse effects of disturbance noises. The algorithm thus works well, and the frequencies of causing routing loops and falling to a local optimum are reduced even if the routing information is disturbed.

On cycles in AS relationships

On cycles in AS relationships

Message-efficient dissemination for loop-free centralized routing

With steady improvement in the reliability and performance of communication devices, routing instabilities now contribute to many of the remaining service degradations and interruptions in modern networks. This has led to a renewed interest in centralized routing systems that, compared to distributed routing, can provide greater control over routing decisions and better visibility of the results. One benefit of centralized control is the opportunity to readily eliminate transient routing loops, which arise frequently after network changes because of inconsistent routing states across devices. Translating this conceptual simplicity into a solution with tolerable message complexity is non-trivial. Addressing this issue is the focus of this paper. We identify when and why avoiding transient loops might require a significant number of messages in a centralized routing system, and demonstrate that this is the case under many common failure scenarios. We also establish that minimizing the number of required messages is NP-hard, and propose a greedy heuristic that we show to perform well under many conditions. The paper's results can facilitate the deployment and evaluation of centralized architectures by leveraging their strengths without incurring unacceptable overhead.

Research on network failure handling technology based on deflection routing

A new deflection routing scheme is proposed to overcome the drawback of existing deflection routing scheme that cannot handle node failure and suffer from routing loops. A new algorithm for computing the backup shortest path tree (SPT) is proposed and a set of procedures are defined for utilizing the backup SPT in case of node or link failure. The failure can be handled swiftly and the backup routes are guaranteed to be loop-free. Experimental results show that the backup routes calculated by proposed scheme are close to the optimal routes by totally re-computing.

Formalization and Analysis of Routing Loops by Inconsistencies in IP Forwarding Tables

The effect of inconsistencies in forwarding tables on the reachability of IP packets is evaluated. To improve a router's availability, in the architecture of current routers, the control element is separated from the forwarding element. However, a router with the current architecture cannot handle a notification for which the topology of the network system changes when its control element has stopped. In such a case, the router cannot update its own forwarding table, and an inconsistency between the forwarding tables of the router and those of the other routers will occur. To investigate the influence of this inconsistency, we formalize the network system, and derive the conditions under which such an inconsistency leads to unreachable routes. After that, the number of routes that are unreachable is evaluated by simulations. These simulations show that routing loops occur more frequently under the condition that a failed node is close to the restarting node or fewer links exist in the network system.

Locally Optimal Source Routing for energy-efficient geographic routing

We analyze the problem of finding an energy-efficient path from a source node to a destination using geographic routing. Existing schemes have neglected the fact that neighbors which are not closer to the destination than the current node can still reduce energy consumption by taking part in the selected path. Moreover, recent works have confirmed that the generally used Unit Disk Graph to model Wireless Sensor Networks does not represent accurately the behavior of real links. We propose a new scheme called Locally Optimal Source Routing (LOSR) that is able to use neighbors which do not provide advance toward the destination to reduce the overall energy consumption while still avoiding routing loops. Using an Automatic Repeat reQuest (ARQ) mechanism hop by hop we overcome the problems caused by errors in radio transmissions and we introduce a novel routing metric, which accounts for those errors in the energy consumption. Our simulation results show that the proposed scheme outperforms existing solutions over a variety of scenarios and network densities.

Backtracking routing mechanism for improving link failure recovery

Failure-insensitive routing is a good mechanism to avoid packet dropping and disconnection of forwarding when some links fail, but multiple failure links may bring routing loop for the mechanism. Backtracking routing algorithm based on inverse shortest path tree rooted at destination is presented. The feasible restoration routing is obtained through searching from the start of the failure link and tracing back to the leaves of the shortest path tree with the destination as the root. The packets are forwarded from the mounted point with smaller sequence to the mount point with bigger sequence to decrease the possible of loop in case of multi-failures. The simulations and analysis indicate that backtracking routing algorithm improves the network survivability especially for large network, at the cost of the computation complexity in the same order as failure insensitive routing.

End-to-end routing behavior in the internet

The large-scale behavior of routing in the Internet has gone virtually without any formal study, the exception being Chinoy's analysis of the dynamics of Internet routing information [Ch93]. We report on an analysis of 40,000 end-to-end route measurements conducted using repeated "traceroutes" between 37 Internet sites. We analyze the routing behavior for pathological conditions, routing stability, and routing symmetry. For pathologies, we characterize the prevalence of routing loops, erroneous routing, infrastructure failures, and temporary outages. We find that the likelihood of encountering a major routing pathology more than doubled between the end of 1994 and the end of 1995, rising from 1.5% to 3.4%. For routing stability, we define two separate types of stability, "prevalence," meaning the overall likelihood that a particular route is encountered, and "persistence," the likelihood that a route remains unchanged over a long period of time. We find that Internet paths are heavily dominated by a single prevalent route, but that the time periods over which routes persist show wide variation, ranging from seconds up to days. About 2/3's of the Internet paths had routes persisting for either days or weeks. For routing symmetry, we look at the likelihood that a path through the Internet visits at least one different city in the two directions. At the end of 1995, this was the case half the time, and at least one different autonomous system was visited 30% of the time.

Avoiding instability during graceful shutdown of multiple OSPF routers

Many recent router architectures decouple the routing engine from the forwarding engine, allowing packet forwarding to continue even when the routing process is not active. This opens up the possibility of using the forwarding capability of a router even when its routing process is brought down for software upgrade or maintenance, thus avoiding the route flaps that normally occur when the routing process goes down. Unfortunately, current routing protocols, such as BGP, OSPF and IS-IS do not support such operation. In an earlier paper, we described an enhancement to OSPF, called the IBB (I'll Be Back) capability, that enables a router to continue forwarding packets while its routing process is inactive. When the OSPF process in an IBB-capable router is inactive, it cannot adapt its forwarding table to reflect changes in network topology. This can lead to routing loops and/or black holes. In this paper, we focus on the loop problem and provide a detailed analysis of how and when loops are formed and propose solutions to prevent them. We develop two necessary conditions for the formation of routing loops in the general case when multiple routers are inactive. These conditions can easily be checked by the neighbors of the inactive routers. Simulations on several network topologies showed that checking the two conditions together signaled a loop in most cases only when a loop actually existed

Formal Security Analysis for Ad-Hoc Networks

In ad-hoc networks, autonomous wireless nodes can communicate by forwarding messages for each other. For routing protocols in this setting, it is known that a malicious node can perform a variety of attacks just by not behaving according to the specification. Whilst secure versions of routing protocols are under development, little effort has been made to formalise the scenario similarly to developments in the realm of traditional security protocols for secrecy and authentication. We present a broadcast process calculus suitable to describe the behaviour of protocols which require a local memory component for every node. By adding annotations for the origin of messages, we are able to formalise a vital security property in this context, called store authorisation. Furthermore, we describe a static analysis for the detection of violations of this property. For a model of the AODV protocol in our calculus, we are then able to deduce that an attacker may introduce a routing loop in certain networks.

On-demand loop-free routing with link vectors

We present the on-demand link vector (OLIVE) protocol, a routing protocol for ad hoc networks based on link-state information that is free of routing loops and supports destination-based packet forwarding. Routers exchange routing information reactively for each destination in the form of complete paths, and each node creates a labeled source graph based on the paths advertised by its neighbors. A node originates a broadcast route request (RREQ) to obtain a route for a destination for which a complete path does not exist in its source graph. When the original path breaks, a node can select an alternative path based on information reported by neighbors, and a node can send a unicast RREQ to verify that the route is still active. A node that cannot find any alternate path to a destination sends route errors reliably to those neighbors that were using it as next hop to the destination. Using simulation experiments in ns2, OLIVE is shown to outperform dynamic source routing, ad hoc on-demand distance vector, optimized link-state routing protocol, and topology broadcast based on reverse-path forwarding, in terms of control overhead, throughput, and average network delay, while maintaining loop-free routing with no need for source routes.

Avoiding Routing Loops on the Internet

Suppose that some particular link in the Internet is currently congested. A natural solution is to try to make packets bypass that link. This can be done by increasing the cost of that link intentionally, say from a 1 to a 2, since the Internet uses shortest-path routing. Unfortunately, however, this often causes temporary loops for packet traveling, called routing loops. In this paper we show that routing loops can be avoided by increasing the cost of the link not directly from a 1 to a 2 but through an intermediate value, a 3, i.e., from a 1 to a 3 and then to a 2. We may need several intermediate values. We show that in this case the greedy strategy, namely, raising the cost as much as possible in each step, is optimal.

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

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.

An intelligent routing and CAC framework for large-scale networks based on cooperative agents

The routing algorithms can be classified into source, distributed and hierarchical routing. Source routing algorithms are conceptually simple, but they suffer from scalability problem. Distributed routing algorithms are more scalable, but loops may occur, which make the routing to fail. Hierarchical routing has been used to cope with the scalability problems of source routing in large internetworks. The hierarchical routing retains many advantages of source routing. It also has some advantages of distributed routing, because the routing computation is shared by many nodes. The traffic control methods for telecommunication networks must be adaptive, flexible, and intelligent. Use of intelligent algorithms based on fuzzy logic, genetic algorithms and neural networks can prove to be efficient for traffic control in telecommunication networks. In this paper, we propose an intelligent routing and Call Admission Control framework, which is based on cooperative agents. The proposed routing algorithm is a combination of source and distributed routing. It uses source routing inside a domain and hop-by-hop routing for inter-domain. The proposed framework is able to avoid flooding and routing loops, reduce the search space, and can be easily scaled-up to cope with large-scale networks. Performance evaluation via simulations shows that the proposed Fuzzy Admission Control and Intra Domain algorithm have better performance than the conventional methods.

Hop-by-hop quality of service routing

Based on the self-adaptive multiple constraints routing algorithm (SAMCRA), an improved and exact version of our QoS routing algorithm, the tunable accuracy multiple constraints routing algorithm (TAMCRA) we have investigated QoS routing in a hop-by-hop manner because it forms the basis of IP networking as e.g. in OSPF. In particular, we studied `hop-by-hop destination based only' (HbHDBO) QoS routing that ignores the source and previous path history (as in current IP routing). We demonstrate that an exact QoS algorithm assures the avoidance of routing loops in this HbHDBO setting. However, despite the use of an exact QoS routing algorithm as SAMCRA, the exact solution cannot be guaranteed with HbHDBO routing. Fortunately, large simulation results on various sizes of random graphs show that the overall quality of the HbHDBO QoS routing is remarkably good. Finally, we show that, by using active networking as opposed to current IP routing, exact QoS routing in a hop-by-hop way can be guaranteed.

Probing the mechanism of rhodopsin-catalyzed transducin activation.

An agonist-bound G protein-coupled receptor (GPCR) induces a GDP/GTP exchange on the G protein alpha-subunit (G alpha) followed by the release of G alpha GTP and G beta gamma which, subsequently, activate their targets. The C-terminal regions of G alpha subunits constitute a major receptor recognition domain. In this study, we tested the hypothesis that the GPCR-induced conformational change is communicated from the G alpha C-terminus, via the alpha 5 helix, to the nucleotide-binding beta 6/alpha 5 loop causing GDP release. Mutants of the visual G protein, transducin, with a modified junction of the C-terminus were generated and analyzed for interaction with photoexcited rhodopsin (R*). A flexible linker composed of five glycine residues or a rigid three-turn alpha-helical segment was inserted between the 11 C-terminal residues and the alpha 5 helix of G alpha(t)-like chimeric G alpha, G alpha(ti). The mutant G alpha subunits with the Gly-loop (G alpha(ti)L) and the extended alpha 5 helix (G alpha(ti)H) retained intact interactions with G beta gamma(t), and displayed modestly reduced binding to R*. G alpha(ti)H was capable of efficient activation by R*. In contrast, R* failed to activate G alpha(ti)L, suggesting that the Gly-loop absorbs a conformational change at the C-terminus and blocks G protein activation. Our results provide evidence for the role of G alpha C-terminus/alpha 5 helix/beta 6/alpha 5 loop route as a dominant channel for transmission of the GPCR-induced conformational change leading to G protein activation.