Routing Update Research Articles

Adapting to route-demand and mobility in ad hoc network routing

We present adapting to route-demand and mobility (ARM), a control mechanism that allows any proactive routing protocol to dynamically adapt in a totally distributed manner to changes in node mobility and workload route-demands. Each node independently maintains a mobility metric indicating how fast its neighborhood is currently changing, and a route-demand metric indicating which destinations are currently involved in data forwarding. Control functions use these metrics to dynamically adjust the period and the content of routing updates. We apply ARM to the destination sequence distance vector (DSDV) protocol, coming up with ARM-DSDV. Simulations for various mobility and workload scenarios show that ARM-DSDV typically achieves better data delivery, while keeping the routing cost at reasonable levels, when compared to DSDV with update period optimized for the scenario.

RANDOMIZED MOBILE AGENT BASED ROUTING IN WIRELESS NETWORKS

We propose a novel approach for shortest path routing in wireless mobile networks. The approach makes use of n mobile agents initially launched from n mobile nodes forming the network. The agents move randomly from node to node and update routing information as they go. The approach is presented in this paper with two protocols. Both of them exhibit good performance in terms of the network and computing resource consumptions. The first protocol relies on independent mobile agents and imposes a minimum bandwidth requirement on individual mobile agents. Each agent carries the link state of its creator and this information remains unchanged except when the mobile agent returns to the home node. The second protocol is a refinement of the first protocol, with some form of interaction between the mobile agents. Each agent maintains the routing table of its creator instead of link state. The randomly walking agents spread the update information and compute the shortest paths via exchanging network state information between the routing tables they carry and the routing tables at the nodes they traverse. The correctness of the protocols is proven. Our analysis shows that the agent cooperation improves the system performance when dealing with topology and link cost changes.

Performance enhancement of IP forwarding by reducing routing table construction time

In previous work, Lampson et al. (1999) proposed an IP lookup algorithm which performs binary searches on prefixes (BSP). The algorithm is attractive for IPv6 because of its bounded worst-case memory requirement. Although for the sake of fast forwarding, the cost paid for the slowing down insertion is reasonable, the performance of routing-table reconstruction in BGP is too time-consuming to handle the frequent route updates. In this letter, we propose a fast forwarding-table construction algorithm which can handle more than 3600 route updates per second. Moreover, it is simple enough to fulfill the need of fast packet forwarding.

Improved AntNet routing

AntNet is a new algorithm for packet routing in communication networks. In AntNet, a group of mobile agents (artificial ants) build paths between pair of nodes, exploring the network concurrently and exchanging data to update routing tables.This work, based in a previous work of the author [3], analyzes AntNet algorithms and proposes improvements, comparing their performance with respect to the original AntNet and other commercial algorithms. Simulation results indicate a better throughput of the improved proposals. So, AntNet and its variant here proposed are promising options for routing in large public networks such as Intemet.

Dissemination of routing information in broadcast networks: OSPF versus IS-IS

OSPF and IS-IS are two main standard link state routing protocols designed to operate in various complex network topologies. One aspect that both protocols handle is the reliable dissemination of routing information over broadcast networks such as Ethernet and FDDI. Both protocols suggest different schemes for this purpose and in this article we compare the two. The performance criteria being checked are: the longest arrival time of a routing update packet at all the routers; the average arrival time of routing update packets at all the routers; the total required bandwidth; and the number of memory accesses a router performs, which is evidence of the amount of internal work it performs. We find that in our model of broadcast networks the scheme suggested in IS-IS is more efficient than that of OSPF in terms of the arrival times of routing update packets. In particular, the average arrival time of routing update packets in OSPF is 2-10 times longer than in IS-IS. In terms of the bandwidth each scheme consumes, there are scenarios where OSPF outperforms IS-IS and vice versa. In terms of the number of memory accesses routers perform in each scheme, IS-IS outperforms OSPF.

A protocol for deadlock-free dynamic reconfiguration in high-speed local area networks

High-speed local area networks (LANs) consist of a set of switches interconnected by point-to-point links, and hosts linked to those switches through a network interface card. High-speed LANs may change their topology due to switches being turned on/off, hot expansion, link remapping, and component failures. In these cases, a distributed reconfiguration protocol analyzes the topology, computes the new routing tables, and downloads them to the corresponding switches. Unfortunately, in most cases, user traffic is stopped during the reconfiguration process to avoid deadlock. These strategies are called static reconfiguration techniques. Although network reconfigurations are not frequent, static reconfiguration such as this may take hundreds of milliseconds to execute, thus degrading system availability significantly. Several distributed real-time applications have strict communication requirements; Distributed multimedia applications have similar, although less strict, quality of service (QoS) requirements. Both stopping packet transmission and discarding packets due to the reconfiguration process prevent the system from satisfying the above requirements. Therefore, in order to support hard real-time and distributed multimedia applications over a high-speed LAN, we need to avoid stopping user traffic and discarding packets when the topology changes. In this paper, we propose a new deadlock-free distributed reconfiguration protocol that is able to asynchronously update routing tables without stopping user traffic. This protocol is valid for any topology, including regular as well as irregular topologies. It is also valid for packet switching as well as for cut-through switching techniques and does not rely on the existence of virtual channels to work. Simulation results show that the behavior of our protocol is significantly better than for other protocols based on stopping user traffic.

IP layer restoration and network planning based on virtual protection cycles

We describe a novel restoration strategy called virtual protection cycles (p-cycles, patents pending) for extremely fast restoration in IP networks. Originally conceived for use in WDM and Sonet transport networks, we outline the adaption of the p-cycle concept to an IP environment. In an IP router-based network, p-cycles are implemented with virtual circuits techniques (such as an MPLS label switched path, or other means) to form closed logical loops that protect a number of IP links, or a node. In the event of failure, packets which would normally have been lost are encapsulated with a p-cycle IP address and reenter the routing table, which diverts them onto a protection cycle. They travel by normal forwarding or label switching along the p-cycle until they reach a node where the continuing route cost to the original destination is lower than that at the p-cycle entry node. Diverted packets are deencapsulated (dropped from the p-cycle) at that node and follow a normal (existing) route from there to their destination. Conventional routing protocols such as OSPF remain in place and operate as they do today, to develop a longer term global update to routing tables. Diversionary flows on the p-cycle inherently cease when the global routing update takes effect in response to the failed link or node. The p-cycle thus provides an immediate real-time detour, preventing packet loss, until conventional global routing reconvergence occurs. The aim of the paper is to explain the basic p-cycle concept and its adaptation to both link and node restoration in the IP transport layer, and to outline certain initial results on the problem of optimized design of p-cycle based IP networks.

A routing protocol for dynamic and large computer networks with clustering topology

The routing decision is one of the important research issues in the network fields. With the rapid development of high-speed networks, multimedia communication networks and mobile computer networks, the hierarchical routing techniques for the dynamic and large networks or high-speed networks have triggered interests among many people worldwide. This paper proposes a hierarchical dynamic routing protocol (HDRP), which can adapt to dynamic and large computer networks (DLCN) with clustering topology. It also gives the main procedures for realizing routing update and routing decision, and the proof of correctness and complexity analysis of the protocol. The performance measures of HDRP, including throughput and average message delay, are evaluated using simulation. The study shows that HDRP provides a new available approach to routing decision for DLCN with clustering topology.

Scanning the literature

There are inherent difficulties in supporting mobility in ATM networks, due to its connection oriented nature. Once mobile users moves out of certain geographic areas, the ongoing connections for the mobile users have to be rerouted. A suitable connection rerouting schemes must exhibit a number of features including: low handoff latency, efficient routes, minimal disruption to the network traffic as well as the necessary route updates. This paper propose and studies 5 different connection rerouting schemes in ATM-based wireless networks. Extensive experiments show that one of the schemes demonstrates superior performance, seems to be ideally suited for the connection rerouting. This scheme is executed in two phrases, real-time and non-real-time: 1) to execute very fast handoff (reroute) scheme using chaining in a real-time with measured time of 6.5 ms; and 2) reroute the connection in non-real-time to achieve more efficient routes if necessary. The conclusion this paper reaches is that simple handoff schemes coupled with a suitable connection management architecture are sufficient for low-bit-rate multimedia application in the ATM-based wireless networks.

Scanning the literature

There are inherent difficulties in supporting mobility in ATM networks, due to its connection oriented nature. Once mobile users moves out of certain geographic areas, the ongoing connections for the mobile users have to be rerouted. A suitable connection rerouting schemes must exhibit a number of features including: low handoff latency, efficient routes, minimal disruption to the network traffic as well as the necessary route updates. This paper propose and studies 5 different connection rerouting schemes in ATM-based wireless networks. Extensive experiments show that one of the schemes demonstrates superior performance, seems to be ideally suited for the connection rerouting. This scheme is executed in two phrases, real-time and non-real-time: 1) to execute very fast handoff (reroute) scheme using chaining in a real-time with measured time of 6.5 ms; and 2) reroute the connection in non-real-time to achieve more efficient routes if necessary. The conclusion this paper reaches is that simple handoff schemes coupled with a suitable connection management architecture are sufficient for low-bit-rate multimedia application in the ATM-based wireless networks.

Internet routing instability

This paper examines the network interdomain routing information exchanged between backbone service providers at the major US 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 led to the loss of internal connectivity in wide-area, national networks. 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 border gateway protocol (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.

Internet routing instability

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.

Adaptive feedback compensation for distributed load-based routing systems in datagram packet-switched communications networks

Routing systems for datagram packet-switched networks' iteratively applying Shortest Path First (SPF) algorithms on load-based link cost metrics exhibit poor stabilization and convergence properties at moderate traffic loads without the addition of experimentally determined Bertsekas Additive Bias Factors to aid in damping undesirable oscillations. Routing systems which iteratively apply SPF Algorithms on load-varying link costs implicitly assume routing assignments can be independently modified without affecting the validity of cost estimates on other links. Even under stationary offered loads, this assumption is less accurate as the load increases due to nonlinear dynamical interactions among traffic flows. Failure to compensate for this independence assumption in iterative SPF computations leads to dynamical instabilities above moderate offered loads. Unfortunately, while Bertsekas Additive Bias Factors improve stability, they also reduce the sensitivity of the routing system to network congestion. As alleviation of traffic congestion is often an important service requirement for a routing system, this is a serious drawback. This paper is motivated by a search for techniques to improve the convergence of routing systems upon near-optimum sets of routing assignments for current traffic conditions, without introducing a loss of congestion sensitivity. Due to the limitations of Markov Chain Models of packet-switching networks for our application, a network simulation is developed which provides a more accurate reflection of network dynamics, as it incorporates bounded queue and minimum interarrival time constraints. Utilizing this simulation, it is demonstrated that a Genetic Algorithm which estimates the near-optimal number of routing assignment changes allowed by the Dijkstra SPF Algorithm during each routing update interval, enables substantial performance advantages for networks operated at or above moderate offered loads. This adaptive feedback compensation technique achieves these performance improvements by avoiding the Kauffman and Eigen Catastrophes, although additional processing and slight increases in routing update packet lengths are required. In a broader context, the technology of adaptive feedback compensation should prove a relevant to a variety of real-time distributed adaptive control applications.

Self-Stabilizing Routing and Related Protocols

Aself-stabilizingsystem is a distributed system which can tolerateany numberandany typeof faults in the history. After the last fault occurs the system converges to alegitimate behavior. The self-stabilization property is very useful for systems in which processors may malfunction for a while and then recover. When there is a long enough period during which no processor malfunctions the system stabilizes.Dynamicdistributed systems are systems in which communication links and processors may fail and recover during normal operation. Such failures could cause partitioning of the system communication graph. The application of self-stabilizing protocols to dynamic systems is natural. Following the last topology change each connected component of the system stabilizes independently. We present self-stabilizing dynamic protocols for a variety of tasks including: routing, leader election, and topology update. For systems that support local broadcasts to neighbors in a single time unit the protocol for each of those tasks stabilizes in Θ(d) time, wheredis theactualdiameter of the system.

Handoffs in Cellular Wireless Networks: The Daedalus Implementation and Experience

Network protocols in cellular wireless data networks must update routes as a mobile host moves between cells. These routing updates combined with some associated state changes are called handoffs. Most current handoff schemes in wireless networks result in data loss or large variations in packet delivery times. Unfortunately, many applications, such as real-time multimedia applications and reliable transport protocols, adapt to long term estimates of end-to-end delay and loss. Violations and rapid fluctuations of these estimates caused by handoff processing often result in degraded performance. For example, loss during handoff adversely affects TCP performance [4], and high packet loss and variable delays result in poor real-time multimedia performance. In this paper, we describe a multicast-based protocol that eliminates data loss and incurs negligible delays during a handoff. The basic technique of the algorithm is to anticipate a handoff using wireless network information in the form of received signal strengths and to multicast data destined for the mobile host to nearby base stations in advance. This routing, combined with intelligent buffering techniques at the base stations, enables very rapid routing updates and eliminates data loss without the use of explicit data forwarding. We have implemented this protocol using IP Multicast and Mobile IP-like routing. In our implementation, handoffs typically take between 8 and 15 ms to complete and result in no data loss.

Route discovery for multistage fabrics in ATM switching nodes

This paper presents an intra-node Route Discovery Protocol (RDP) applicable to multistage switch fabrics in nodes of ATM Local Area Networks (LANs), as well as in transit nodes of future high-speed Metropolitan or Wide Area Networks (MANs or WANs). The proposed RDP automatically builds and periodically updates routing tables in each network adapter. These routing tables contain the mapping between the logical adapter addresses and the currently available physical routes through the multistage switch fabric to all other adapters attached to the node. In addition, functional entities located at specific adapters are detected and associated with physical routes in the routing tables. Detecting all routes during system startup is the basis for fast connection setup with low latency. By periodically monitoring all possible table entries, our protocol provides continuous supervision of the node's internal link status and can support possible higher-layer extensions to perform load balancing over alternative routes. Small control buffers in network adapters, which are typical for practical implementations, may lead to overflow conditions and, thus, to incompletely updated routing tables. An effective stochastic solution to this problem is presented and it will be shown through probabilistic analysis that reasonably small buffer sizes suffice for executing RDP with sufficient robustness.

Traffic pattern based mobile routing scheme

This paper presents a novel routing scheme for wireless mobile networking which is adaptive to mobile traffic patterns. We propose a selective location information update scheme to accommodate the need for optimal traffic routing as well as minimizing network bandwidth consumption by routing updates. Performance analysis shows that this adaptive routing scheme is highly efficient over a wide range of traffic patterns.

Integrating security in inter-domain routing protocols

Network routing protocols work in a vulnerable environment. Unless protected by appropriate security measures, their operation can be easily subverted by intruders capable of modifying, deleting or adding false information in routing updates. This paper first analyses threats to the secure operation of inter-domain routing protocols, and then proposes various counter measures to make these protocols secure against external threats.

Convergence of gradient projection routing methods in an asynchronous stochastic quasi-static virtual circuit network

The convergence of the gradient projection algorithms for optimal routing in virtual circuit data networks proposed by D.P. Bertsekas (1982) is studied. The routing model explicitly takes into account stochastic generation and termination of virtual circuits, distributed asynchronous routing updates, inaccurate flow measurement, and delays in forwarding control packets. The problem of assigning paths for incoming sessions (or virtual circuits) to implement the gradient projection algorithms is also studied. A metering rule based on deficiency in a desired number of virtual circuits is proposed and analyzed. It is shown that the proposed metering rule is better than a randomized rule in some sense. The gradient projection routing algorithms implemented either by the metering rule or the randomized rule are shown to converge to a neighborhood of a long-term optimal routing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Distributed asynchronous optimal routing in data networks

In this paper we study the performance of a class of distributed optimal routing algorithms of the gradient projection type under weaker and more realistic assumptions than those considered thus far. In particular, we show convergence to an optimal routing without assuming synchronization of computation at all nodes and measurement of link lengths at all links, while taking into account the possibility of link flow transients caused by routing updates. This demonstrates the robustness of these algorithms in a realistic distributed operating environment.