Showing papers on "Routing table published in 1999"

Distributed quality-of-service routing in ad hoc networks

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

Fast address lookups using controlled prefix expansion

Abstract: Internet (IP) address lookup is a major bottleneck in high-performance routers. IP address lookup is challenging because it requires a longest matching prefix lookup. It is compounded by increasing routing table sizes, increased traffic, higher-speed links, and the migration to 128-bit IPv6 addresses. We describe how IP lookups and updates can be made faster using a set of of transformation techniques. Our main technique, controlled prefix expansion, transforms a set of prefixes into an equivalent set with fewer prefix lengths. In addition, we use optimization techniques based on dynamic programming, and local transformations of data structures to improve cache behavior. When applied to trie search, our techniques provide a range of algorithms (Expanded Tries) whose performance can be tuned. For example, using a processor with 1MB of L2 cache, search of the MaeEast database containing 38000 prefixes can be done in 3 L2 cache accesses. On a 300MHz Pentium II which takes 4 cycles for accessing the first word of the L2 cacheline, this algorithm has a worst-case search time of 180 nsec., a worst-case insert/delete time of 2.5 msec., and an average insert/delete time of 4 usec. Expanded tries provide faster search and faster insert/delete times than earlier lookup algirthms. When applied to Binary Search on Levels, our techniques improve worst-case search times by nearly a factor of 2 (using twice as much storage) for the MaeEast database. Our approach to algorithm design is based on measurements using the VTune tool on a Pentium to obtain dynamic clock cycle counts. Our techniques also apply to similar address lookup problems in other network protocols.

A wireless hierarchical routing protocol with group mobility

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

IP lookups using multiway and multicolumn search

Abstract: IP address lookup is becoming critical because of increasing routing table sizes, speed, and traffic in the Internet. Given a set S of prefixes and an IP address D, the IP address lookup problem is to find the longest matching prefix of D in set S. This paper shows how binary search can be adapted for solving the best-matching prefix problem. Next, we show how to improve the performance of any best-matching prefix scheme using an initial array indexed by the first X bits of the address. We then describe how to take advantage of cache line size to do a multiway search with six-way branching. Finally, we show how to extend the binary search solution and the multiway search solution for IPv6. For a database of N prefixes with address length W, naive binary search would take O(W*log N); we show how to reduce this to O(W+log N) using multiple-column binary search. Measurements using a practical (Mae-East) database of 38000 entries yield a worst-case lookup time of 490 ns, five times faster than the Patricia trie scheme used in BSD UNIX. Our scheme is attractive for IPv6 because of its small storage requirement (2N nodes) and speed (estimated worst case of 7 cache line reads per lookup).

A simple approximation to minimum-delay routing

Abstract: The conventional approach to routing in computer networks consists of using a heuristic to compute a single shortest path from a source to a destination. Single-path routing is very responsive to topological and link-cost changes; however, except under light traffic loads, the delays obtained with this type of routing are far from optimal. Furthermore, if link costs are associated with delays, single-path routing exhibits oscillatory behavior and becomes unstable as traffic loads increase. On the other hand, minimum-delay routing approaches can minimize delays only when traffic is stationary or very slowly changing.We present a "near-optimal" routing framework that offers delays comparable to those of optimal routing and that is as flexible and responsive as single-path routing protocols proposed to date. First, an approximation to the Gallager's minimum-delay routing problem is derived, and then algorithms that implement the approximation scheme are presented and verified. We introduce the first routing algorithm based on link-state information that provides multiple paths of unequal cost to each destination that are loop-free at every instant. We show through simulations that the delays obtained in our framework are comparable to those obtained using the Gallager's minimum-delay routing. Also, we show that our framework renders far smaller delays and makes better use of resources than traditional single-path routing.

A unified routing scheme for ad-hoc internetworking

Abstract: Routing table update messsages that include both network-level and link-level addresses of nodes of a computer network are exchanged among the nodes of the computer network. Further, a routing table maintained by a first one of the nodes of the computer network may be updated in response to receiving one or more of the update messages. The shortest distance to the destination node may be determined according to one or more link-state and/or node-state metrics regarding communication links and nodes along the path to the destination node. Also, the nodal characteristics of the nodes of the computer system may be exchanged between neighbor nodes, prior to updating the routing table.

MCEDAR: multicast core-extraction distributed ad hoc routing

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

Compact routing with minimum stretch

Abstract: We present the first universal compact routing algorithm with maximum stretch bounded by 3 that uses sublinear space at every vertex. The algorithm uses local routing tables of size O(n2/3log4/3n) and achieves paths that are most 3 times the length of the shortest path distances for all nodes in an arbitrary weighted undirected network. This answers an open question of Gavoille and Gengler who showed that any universal compact routing algorithm with maximum stretch strictly less than 3 must use ?(n) local space at some vertex.

Load-sensitive routing of long-lived IP flows

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

Dynamic wavelength routing using congestion and neighborhood information

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

Apparatus and method for unilateral topology discovery in network management

Abstract: A system for reducing the cost of network managment by using a proxy agent and subchannel communications so fewer SNMP licenses and fewer protocol stacks are needed. Subchannel communication is achieved in a plurality of different embodiments. Embodiments having single subchannel transceivers, multiple transceivers, single multiplexer and multiple multiplexers are disclosed. An NMS process using routing table CRC to automatically detect when the NMS topology information is incorrect and automated topology discovery is disclosed. A process for automated discovery of redundant cables during automated topology discovery is disclosed.

Traffic routing in small wireless data networks

Abstract: A method for relaying, at a node (10) within a wireless network, received message data appended with route identifier and route update message, including updating a route table based on route update message appended to received message data (34), selecting a neighboring node based on the route table (44), replacing the route identifier and the route update message based on the updated route table (48), transmitting the message data appended with the replaced route identifier and the replaced update message to the selected neighboring node (50).

Constructing optimal IP routing tables

Abstract: The Border Gateway Protocol (BGP) populates Internet backbone routers with routes or prefixes. We present an algorithm to locally compute (without any modification to BGP) equivalent forwarding tables that provably contain the minimal number of prefixes. For large backbone routers, the Optimal Routing Table Constructor (ORTC) algorithm that we present produces routing tables with roughly 60% of the original number of prefixes. The publicly available MaeEast database with 41315 prefixes reduces to 23007 prefixes when ORTC is applied. We present performance measurements on four publicly available databases and a formal proof that ORTC does produce the optimal set of routes.

Origins of Internet routing instability

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

Explicit routing algorithms for Internet traffic engineering

Abstract: This paper considers explicit routing algorithms for Internet traffic engineering. Explicit routing is seen to be a much more capable solution for improving network utilization than the current destination-based routing and the multi-protocol label switching (MPLS) standard has made explicit routes implementable. ISP can now have fine granularity control over the traffic distribution across their backbones by carefully overlaying explicit routes over the physical network. The basic traffic engineering problem is how to set up explicit routes to meet bandwidth demands between the edge nodes of the network and at the same time to optimize the network performance. We model the traffic engineering problem as an optimization problem with the objective of minimizing congestion and maximizing potential for traffic growth. We present two mathematical formulations, one linear programming for the case of allowing demand bifurcation and one integer programming for the case of disallowing demand bifurcation. While the bifurcation case can be solved to optimality, we show that the non-bifurcation case is NP-hard. Four heuristic schemes are proposed for the non-bifurcation case, with the most sophisticated one being based on re-routing of split demands in the optimal solution of the bifurcation case. The performance of these heuristic schemes are tested in a large backbone topology. Our results show that shortest-path and minimum hop algorithms, although widely used in current routing protocols, perform poorly, white the re-routing approach performs best.

Two phase local mobility scheme for wireless access to packet based networks

Abstract: Local mobility within a subnet is supported by classifying wireless base stations, and the routers used to forward packets to those base stations, within defined domains. Domains are defined to incorporate a subnet having a plurality of base stations. Base stations are used by mobile devices to attach to the wired portion of a packet-based network, such as the Internet, and exchange packets thereover with a correspondent node. Packets sent from the correspondent node to the mobile device have a packet destination address corresponding to the mobile device. The mobile device retains this address for the duration of time it is powered up and attached to the Internet via any base station within a given domain. Host-based routing is utilized to update routing table entries corresponding to the mobile device at routers incorporated within a single domain. The routing table entries are established and updated via path setup schemes to convey packets destined for the mobile device along the proper established path through the domain routers and base stations, regardless of the domain base station through which the mobile device is attached. Path setup schemes utilize power up, refresh, and handoff path setup messages to maintain the proper relationship between router interfaces and packet addresses for routing table entries.

A new approach to on-demand loop-free multipath routing

Abstract: We present and verify ROAM, an on-demand routing algorithm that maintains multiple loop-free paths to destinations. Each router maintains entries only for those destinations for which data flows through the router which reduces storage space requirements and the amount of bandwidth needed to maintain correct routing tables. In ROAM, routes are established and maintained on demand using diffusing computations. A router does not send updates for active destinations, unless its distance to them increases beyond a given threshold. ROAM maintains a state that informs routers when a destination is unreachable and prevents routers from sending unnecessary search packets attempting to find paths to an unreachable destination. ROAM is shown to converge in a finite time after an arbitrary sequence of topological changes and is shown to be loop-free at every instant. The time and communication complexities of ROAM are analyzed.

System for communicating labeled routing trees to establish preferred paths and source routes with local identifiers in wireless computer networks

Abstract: One or more labeled routing trees (LRTS) are produced at a router of a computer network according to a shortest path determination made over a partial topology graph of the network, which graph is produced according to knowledge of adjacent links of the router and one or more LRTs of neighboring routers. The LRTs of the router may be updated in response to receipt of routing state update messages, and such messages may include local link identifiers assigned by a head of a link to which the identifiers pertain, and node parameters of a tail of the link to which the local link identifiers pertain. The routing state update messages may be transmitted within the network: (i) in response to a new destination node being detected by an existing node within the network, (ii) in response to a destination becoming unreachable by a collection of the existing nodes, (iii) in response to the change in the cost of a path to at least one destination exceeding a threshold and/or (iv) in situations where a routing loop may be encountered among two or more of the nodes of the network (e.g., at times when a path implied in the LRT of the router leads to a loop).

Mobile IP mobile router

Abstract: Methods and apparatus for implementing a Mobile IP mobile router are provided. In accordance with one aspect, the Home Agent receives a registration request packet. The registration request packet may include a care-of address for the mobile router. Networks associated with the mobile router are then identified. The Home Agent then updates a routing table to associate the identified networks with the care-of address. In addition, the Home Agent updates a mobility binding table with the care-of address for the mobile router. In accordance with another aspect, routing information is exchanged between the Home Agent and the mobile router. A routing table associated with at least one of the Home Agent and the mobile router is then updated as appropriate to include the exchanged routing information.

High-performance IP routing table lookup using CPU caching

Abstract: Wire-speed IP (Internet Protocol) routers require very fast routing table lookup for incoming IP packets. The routing table lookup operation is time consuming because the part of an IP address used in the lookup, i.e., the network address portion, is variable in length. This paper describes the routing table lookup algorithm used in a cluster-based parallel IP router project called Suez. The innovative aspect of this algorithm is its ability to use CPU caching hardware to perform routing table caching and lookup directly by carefully mapping IP addresses to virtual addresses. By running a detailed simulation model that incorporates the performance effects of the CPU memory hierarchy against a packet trace collected from a major network router, we show that the overall performance of the proposed algorithm can reach 87.87 million lookups per second for a 500-MHz Alpha processor with a 16-KByte L1 cache and a 1-MByte L2 cache. This result is one to two orders of magnitude faster than previously reported results on software-based routing table lookup implementations. This paper also reports the performance impacts of various architectural parameters in the proposed scheme and its storage costs, together with the measurements of an implementation of the proposed scheme on a Pentium-II machine running Linux.

Wireless access to packet-based networks

Abstract: Domains are defined to incorporate a subnet including a plurality of base stations and routers. Base stations are used by mobile devices to attach to the wired portion of a packet-based network, such as the Internet, and exchange packets thereover with a correspondent node. Local mobility between domain base stations is provided by including and updating routing table entries at domain routers and base stations for forwarding packets having a mobile device's address as a destination address to the mobile device. Packets are delivered to the mobile device regardless of the domain base station to which the mobile device is attached. When a mobile device is attached to a base station included within a foreign domain, a care-of address is assigned, and packets are tunneled for delivery of packets to the mobile device. Only one care-of address is required per mobile device per foreign domain. Routing table entries used for packet delivery are updated on a purely local subnet basis within domains, whether home domain or foreign domain, making handoffs between base stations substantially transparent to the home agent and the correspondent node.

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

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

Using alternate routes for fail-over in a communication network

Abstract: Using alternate routes for fail-over in a communication network involves maintaining a preferred route and an alternate route in a routing table and routing protocol messages according to the alternate route when the preferred route is unavailable. A node obtains multiple routes for a destination, prioritizes the routes, and installs multiple routes in the routing table, including at least the preferred route and the alternate route. When the node receives a protocol message, the node searches the routing table for a highest priority route that is available for routing the protocol message, and routes the protocol message according to the highest priority route that is available for routing the protocol message. When a route becomes unavailable, the node updates the routing table to indicate that the route is unavailable, and may compute new routes and/or re-prioritize existing routes.

A novel IP-routing lookup scheme and hardware architecture for multigigabit switching routers

Abstract: One of the pertinent design issues for new generation IP routers is the route-lookup mechanism. For each incoming IP packet, the IP routing is required to perform a longest-prefix matching on the route lookup in order to determine the packet's next hop. This study presents a fast unicast route-lookup mechanism that only needs tiny SRAM and can be implemented using a hardware pipeline. The forwarding table, based on the proposed scheme, is small enough to fit into a faster SRAM with low cost. For example, a large routing table with 40000 routing entries can be compacted into a forwarding table of 450-470 kbytes costing less than US$30. Most route lookups need only one memory access; no lookup needs more than three memory accesses. When implemented using a hardware pipeline, the proposed mechanism can achieve one routing lookup every memory access. With current 10-ns SRAMs, this mechanism furnishes approximately 100/spl times/10/sup 6/ routing lookups/s, which is much faster than any current commercially available routing-lookup scheme.

Quality-of-service routing using maximally disjoint paths

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

Packet forwarding apparatus with a flow detection table

Abstract: A packet forwarding apparatus provided with a plurality of line interface units, comprises a routing processing unit for referring to a routing table, based on header information of received packet to specify one of output lines to output the received packet, a flow detection unit for referring to an entry table, in which a plurality of entries with flow conditions and control information are registered, to retrieve control information defined by the entry with a flow condition which coincides with that of the header information of the received packet, and a packet forwarding unit for transferring the received packet to one of the line interface units connected to the output line specified by the routing processing unit. The entry table id divided into a plurality of subtables corresponding to the values of flow attributes associated with the received packets and the flow detection unit retrieves the control information from one of said subtables specified by the value of the flow attribute corresponding to the received packet.

Apparatus and methods for routerless layer 3 forwarding in a network

Abstract: A layer 3 forwarding method for layer 3 forwarding an individual packet from a station I to a station II wherein the packet's layer 2 destination includes a router within the network which is reachable from a network element A via which stations I and II are connected to the network, the router storing ARP information, the method including providing network element A with a capability to perform layer 3 forwarding of a packet from station I to station II, wherein the providing step includes learning, on the part of network element A, of forwarding information used by the router to forward packets from station I to station II, by reading the ARP information of the router and performing layer 3 forwarding on the individual packet, at network element A.

Method and apparatus for updating and synchronizing forwarding tables in a distributed network switch

Abstract: A mechanism and technique updates and synchronizes forwarding tables contained on line cards that are interconnected by a switch fabric of a distributed network switch. The network switch is preferably a L3 or L4 switch comprising a plurality of forwarding engines distributed among the line cards. Each forwarding engine has an associated forwarding table, which preferably includes a L2 portion and L3/L4 portions. The L2 portion of the table is used to execute forwarding decision operations for frames forwarded among ports of the line cards, whereas the L3/L4 portions of the table are used to execute shortcut and forwarding operations for frames routed among the ports. The mechanism comprises a media access control (MAC) notification (MN) frame for updating and synchronizing the location of a destination port stored in the L2 portions of the forwarding tables.

On fast address-lookup algorithms

Abstract: The growth of the Internet and its acceptance has sparkled keen interest in the research community in respect to many apparent scaling problems for a large infrastructure based on IP technology. A self-contained problem of considerable practical and theoretical interest is the longest-prefix lookup operation, perceived as one of the decisive bottlenecks. Several novel approaches have been proposed to speed up this operation that promise to scale forwarding technology into gigabit speeds. This paper surveys these new lookup algorithms and classifies them based on applied techniques, accompanied by a set of practical requirements that are critical to the design of high-speed routing devices. We also propose several new algorithms to provide lookup capability at gigabit speeds. In particular, we show the theoretical limitations of routing table size and show that one of our new algorithms is almost optimal, while requiring only a small number of memory accesses to perform each address lookup.