Showing papers on "Static 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.

End-to-end routing behavior in the Internet

Abstract: The large-scale behavior of routing In the Internet has gone virtually without any formal study, the exceptions being Chinoy's (1993) analysis of the dynamics of Internet routing information, and work, similar in spirit, by Labovitz, Malan, and Jahanian (see Proc. SIGCOMM'97, 1997). We report on an analysis of 40000 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 3.3%. 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 two-thirds 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.

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

QoS routing mechanisms and OSPF extensions

Abstract: This paper presents and discusses path selection algorithms to support QoS routes in IP networks. The work is carried out in the context of extensions to the OSPF protocol, and the initial focus is on unicast flows, although some of the proposed extensions are also applicable to multicast flows. We first review the metrics required to support QoS, and then present and compare several path selection algorithms, which represent different trade-offs between accuracy and computational complexity. We also describe and discuss the associated link advertisement mechanisms, and investigate some options in balancing the requirements for accurate and timely information with the associated control overhead. The overall goal of this study is to identify a framework and possible approaches to allow deployment of QoS routing capabilities with the minimum possible impact to the existing routing infrastructure.

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.

An efficient message authentication scheme for link state routing

Abstract: We study methods for reducing the cost of secure link state routing. In secure link state routing, routers may need to verify the authenticity of many routing updates, and some routers such as border routers may need to sign many routing updates. Previous work such as public-key based schemes are very expensive computationally or have certain limitations. This paper presents an efficient solution, based on a detection-diagnosis-recovery approach, for the link state routing update authentication problem. Our scheme is scalable to handle large networks, applicable to routing protocols that use multiple-valued cost metrics, and applicable even, when link states change frequently.

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.

Service request routing using quality-of-service data and network resource information

Abstract: A routing apparatus is located at an outbound “edge” of an administrative domain or at an inbound “edge” of an ISP or other network facility. The apparatus, which is preferably implemented in software, includes a “dispatcher.” The dispatcher has a database associated therewith in which information about a “current state” of the network or some resource therein is collected and maintained. The “current state” information is generally of two types: quality-of-service (Q-o-S) information associated with transactions involving a particular Web server, or more general network resource availability information. According to the invention, a routing “policy” is defined at the dispatcher using at least one routing rule having a condition and an action. As service requests arrive at the dispatcher, each of the requests is routed to a destination by testing the current state information against the condition.

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.

Method and apparatus for routing emergency services calls in an intelligent network

Abstract: Emergency services calls may be alternate-routed in an intelligent network having at least one Service Control Point (SCP) with access to a routing table, a plurality of Service Switching Points (SSP) equipped with point-in-call triggers and one or more emergency services stations (PSAP). The routing table lists a routing number for each of the emergency services stations. The alternate routing involves presetting a point-in-call trigger at a Service Switching Point to operate at a predetermined point in a call for emergency services. During subsequent processing of an emergency services call, the trigger interrupts processing of the call and and prompts transmission to the SCP of a query signalling message requesting routing information. Upon receipt, the SCP accesses the routing table in dependence upon parameters in the query signalling message and obtains a routing number for a selected emergency services operator station, forms a response signalling message including the routing number and returns such response signalling message to the SSP. Upon receipt of the response signalling message, the SSP detects the routing number, and routes the call to the emergency services operator station. There is also provided a method of translating signalling message parameters from a mobile protocol to an intelligent network protocol, and vice versa, to enable emergency services calls from mobile users to be routed to one or more PSAPs in the intelligent network.

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.

Method and apparatus for dynamically routing calls in an intelligent network

Abstract: A method, apparatus and system for dynamically routing selected calls through an intelligent switched telephone network are described The method leverages the resident switching power in the Public Switched Telephone Network (202) by departing from the Advanced Intelligent Network (AIN) call model while adhering to the basic principles of ISUP common channel signaling to introduce new flexibility in call routing Using the method, calls can be efficiently routed and rerouted through the network Control of a call can be effected by either the called party or the calling party The method can be practised using either a virtual switching point (VSP) (208) or an ISTP (232) The VSP is a physical node in the signaling plane of the network and a virtual node in the switching plane Calls are routed to the VSP using dedicated trunk groups which may be loop-back ISUP trunks (234) or inter-switch ISUP trunks (212) Calls are routed to the dedicated trunk groups using standard routing translation tables and methods The advantage is a new level of flexibility in call routing control that permits the rapid introduction of new services which include features that could not be efficiently accommodated using prior methods of call routing

QoS based routing algorithm in integrated services packet networks

Abstract: In this paper we study QoS based routing algorithm for supporting resource reservation in high-speed Integrated Services Packet Network (ISPN). Recently, this problem was proved to be NP-complete. However, when the considered QoS constraints are bandwidth, delay, delay jitter, and loss free, we have shown that by employing Weighted Fair Queueing (WFQ) service discipline, the complexity of the problem could be reduced to that of shortest path routing without any QoS constraints. Then such a multiple QoS constrained route could be searched in polynomial time. We also present the routing algorithm (called "QoSR/sub BF/"), which is a modified version of Bellman-Ford shortest path algorithm. Simulation results show that QoSR/sub BF/ has better performance compared to the existing QoS routing algorithms.

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.

Dynamic wavelength allocation in all-optical ring networks

Abstract: We focus on wavelength allocation schemes for all-optical WDM ring networks. For an N node network we characterize the traffic by its load L/sub max/ (the maximum number of lightpaths that share a link) and do not assume knowledge of the arrival/departure processes. We prove that shortest path routing produces a routing which has at most twice the load of the optimal solution. We show that at least 0.5 L/sub max/ log/sub 2/N+L/sub max/ wavelengths are required by any algorithm in the worst case, and develop an algorithm which requires up to 3 L/sub max/ log/sub 2/N wavelengths. For the case when the load is high and blocking is necessary we present an improved algorithm.

Method and apparatus for determining a routing table for each node in a distributed nodal system

Abstract: A method enables each node in a multi-nodal network to construct a routing table to all other nodes in the network. Each "home" or originating node performs a method which includes the steps of: transmitting a query to all immediate neighbor nodes and recording in a routing table, responses received which identify the neighbor node at the terminus of each link; transferring to each neighbor node, home node routing table entries and receiving routing table entries from each neighbor node; and, for each routing table entry to a node that is received from a neighbor node, if the route indicator is already present in the home node routing table, ignoring the entry; if the new entry indicates a route to a new node, entering the new node and a route identifier; and if the entry indicates a route to a node for which there is already an entry in the home node routing table, noting the new entry as a lower priority route to the node. Once the aforementioned procedure is repeated a number of times, each node in the multi-nodal network includes routes to all nodes in the network, with the routes having automatically been prioritized in accordance by sequence of receipt.

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.

Path switching-a quasi-static routing scheme for large-scale ATM packet switches

Abstract: A quasi-static routing scheme called path switching for large-scale ATM packet switch systems is proposed. Previously the Clos network has been used as the model for many large-scale ATM switch architectures, in which the most difficult issue is path and bandwidth assignment for each connection request. The static routing scheme, such as multirate circuit switching, does not fully exploit the statistical multiplexing gain. In contrast, the dynamic routing scheme, such as straight matching, requires slot-by-slot computation of route assignment. Path switching is a compromise of these two routing schemes. It uses a predetermined periodical connection pattern in the central stage, look-ahead selection in the input stage, and output queueing in the last stage. The scheduling of path switching consists of capacity assignment and route assignment. The capacity assignment is constrained by the quality of service of connection requests. The route assignment is based on the timespace interleaving of the coloring of bipartite multigraphs. We show that path switching can handle multirate and multimedia traffic effectively in the Clos network.

Virtual circuit switching architecture

Abstract: A virtual architecture for enabling direct point-to-point communications between any processes on a network cloud utilizes a process record in which information relevant to the process is stored and propagated through a parent/child hierarchy of connection service processes and information service processes. Process records and information relating to processes are propagated throughout private clouds, public clouds and interconnecting global services to facilitate both activity based network routing and load based network routing without the use of predetermined network routing mechanisms.

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.