Showing papers on "Routing protocol published in 1990"

Multiple protocol routing

Abstract: A method for connecting a network so that TCP/IP and OSI 8473 packets may be routed in the same domain. The independence of the addresses is maintained: one device in the network may be assigned only a TCP/IP address, and another device may be assigned only a ISO 8473 address. Furthermore, all of the routers share link state information by using a common link state packet format (such as the ISO 10589 format); thus routes through the network may be computed without regard for the protocols supported by the routers along the route. Where necessary, packets are encapsulated and forwarded through routers which are not capable in the protocol of the packet. In some disclosed embodiments, all of the routers in a given area support a given protocol (or, in fact, have identical capabilities, in which case encapsulation is not required). In these embodiments, the encapsulation is performed by suitable modifications to each router's packet forwarding procedures. In other disclosed embodiments, these topological restrictions are removed, and the network is expanded to support additional protocols. In these embodiments, the Dijkstra algorithm is also modified to generate information on how to encapsulate and forward packets through the network.

Use of OSI IS-IS for routing in TCP/IP and dual environments

Abstract: This RFC specifies an integrated routing protocol, based on the OSI Intra-Domain IS-IS Routing Protocol, which may be used as an interior gateway protocol (IGP) to support TCP/IP as well as OSI. This allows a single routing protocol to be used to support pure IP environments, pure OSI environments, and dual environments. This specification was developed by the IS-IS working group of the Internet Engineering Task Force.

Dynamic routing system for a multinode communications network

Abstract: A communication network having a multiplicity of nodes provides efficient exchange of messages between the nodes. The messages may be originated and received by the computers of a parallel computer system, the processors and associated memories of which are connected to each node. Each node includes a routing system which results in efficient system performance for the parallel computer system associated with the nodes. The messages have control information (a message tag) to which the routing system at each node is responsive. The tag contains data identifying the destination node of the message in the network and prioritization data which, when the message is generated, is initialized to have a value (weight) corresponding to the length (number of links) of the minimal path from the source node where the message originates to the destination node of the message. The routing system utilizes the weights to establish message priority. The routing system receives and sends messages not exceeding the number of links connected thereto on each cycle such that messages flow in and flow out of each routing node on each cycle without being held or stored in queues in the node. Messages of lesser priority are switched by the router to alternate links in accordance with their weights thereby dynamically routing and resolving conflicts among messages.

A detailed router for field-programmable gate arrays

Abstract: A detailed routing algorithm, called the coarse graph expander (CGE), that has been designed specifically for field-programmable gate arrays (FPGAs) is described. The algorithm approaches this problem in a general way, allowing it to be used over a wide range of different FPGA routing architectures. It addresses the issue of scarce routing resources by considering the side effects that the routing of one connection has on another, and also has the ability to optimize the routing delays of time-critical connections. CGE has been used to obtain excellent routing results for several industrial circuits implemented in FPGAs with various routing architectures. The results show that CGE can route relatively large FPGAs in very close to the minimum number of tracks as determined by global routing, and it can successfully optimize the routing delays of time-critical connections. CGE has a linear run time over circuit size. >

NEST: a network simulation and prototyping testbed

Abstract: The Network Simulation Testbed (NEST) is a graphical environment for simulation and rapid-prototyping of distributed networked systems and protocols. Designers of distributed networked systems require the ability to study the systems operations under a variety of simulated network scenarios. For example, designers of a routing protocol need to study the steady-state performance features of the mechanism as well as its dynamic response to failure of links or switching nodes. Similarly, designers of a distributed transaction processing system need to study the performance of the system under a variety of load models as well as its response to failure conditions. NEST provides a complete environment for modeling, execution and monitoring of distributed systems of arbitrary complexity.NEST is embedded within a standard UNIX environment. A user develops a simulation model of a communication network using a set of graphical tools provided by the NEST generic monitor tools. Node functions (e.g., routing protocol) as well as communication link behaviors (e.g., packet loss or delay features) are typically coded by the user in C; in theory, any high-level block-structured language could be supported for this function. These procedures provided by the user are linked with the simulated network model and executed efficiently by the NEST simulation server. The user can reconfigure the simulation scenario either through graphical interaction or under program control. The results of an execution can be graphically monitored through custom monitors, developed using NEST graphical tools.NEST may thus be used to conduct simulation studies of arbitrary distributed networked systems. However, unlike pure simulation tools, NEST may also be used as an environment for rapid prototyping of distributed systems and protocols. The actual code of the systems developed in this manner can be used at any development stage as the node functions for a simulation. The behavior of the system may be examined under a variety of simulated scenarios. For example, in the development of a routing protocol for a mobile packet radio network, it is possible to examine the speed with which the routing protocol responds to changes in the topology, the probability and expected duration of a routing loop. The actual code of the routing protocol may be embedded as node functions within NEST. The only modifications of the code will involve use of NEST calls upon the simulated network to send, receive or broadcast a message. Thus NEST is particularly useful as a tool to study the performance behavior of real (or realisticly modeled) distributed systems in response to simulated complex dynamical network behaviors. Such dynamic response is typically beyond the scope of analytical techniques restricted to model steady-state equilibrium behaviors.Traditional approaches to simulation are either language-based or model-based. Language-based approaches (e.g., Simula, Simscript) provide users with specialized programming language constructs to support modeling and simulation. The key advantage of these approaches is their generality of applications. These approaches, however, are fundamentally limited as tools to study complex distributed systems: First, they separate the tasks of modeling and simulation from those of design and development. A designer of a network protocol is required to develop the code in one environment using one language (e.g., C), while simultaneously developing a consistent simulation model (e.g., in Simscript). The distinctions between the simulation model and the actual system may be significant enough to reduce the effectiveness of simulation. This is particularly true for complex systems involving a long design cycle and significant changes. Second, these approaches require the modeler to efficiently manage the complexity of scheduling distributed system models (under arbitrary network scenarios).Model-based approaches (e.g., queuing-network simulators such as IBM's RESQ [12]) provide users with extensive collections of tools supporting a particular simulation-modeling technique. The key advantage of model-based approaches is the efficiency with which they may handle large-scale simulations by utilizing model-specific techniques (e.g., fast algorithms to solve complex queuing network models). Their key disadvantage is a narrower scope of applications and questions that they may answer. For example, it is not possible within a pure queuing-network model to model and analyze complex transient behaviors (e.g., formation of routing loops in a mobile packet radio network). The model-based approach, like the language-based approaches, suffers from having simulation/testing separated from design/development. It has the additional important disadvantage of requiring users to develop in-depth understanding of the modeling techniques. Designers of distributed database transaction systems are often unfamiliar with queuing models.NEST pursues a different approach to simulation studies: extending a networked operating system environment to support simulation modeling and efficient execution. This environment-based approach to simulation shares the generality of its modeling power with language-based approaches. NEST may be used to model arbitrary distributed interacting systems. NEST also shares with the language-based approach an internal execution architecture that accomplishes very efficient scheduling of a large number of processes. However, unlike language-based approaches, the user does not need to be concerned with management of complex simulation scheduling problems. Furthermore, NEST does not require the user to master or use a separate simulation language facility; the processes of design, development and simulation are fully integrated. The user can study the behavior of the actual system being developed (at any level of detail) under arbitrary simulated scenarios. The routing protocol designer, for example, can attach the routing protocol designed (actual code with minor adjustments) to a NEST simulation and study the system behavior. As the system changes through the design process, new simulation studies may be conducted by attaching the new code to the same simulation models. NEST can thus be used as an integral part of the design process along with other tools (e.g., for debugging).In similarity to model-based approaches, NEST is specifically targeted toward a limited scope of applications: distributed networked systems. NEST supports a built-in customizable communication network model. However, this scope has been sufficiently broad to support studies ranging from low-level communication protocols to complex distributed transaction processing systems, avionic systems and even manufacturing processes.The environment-based approach to simulation offers a few important attractions to users: 1. Simulation is integrated with the range of tools supported by the environment.The user can utilize graphics, statistical packages, debuggers and other standard tools of choice in the simulation study.Simulation can become an integral part of a standard development process.2. Users need not develop extensive new skills or knowledge to pursue simulation studies.3. Standard features of the environment can be used to enhance the range of applicability.NEST simulation is configured as a network server with monitors as clients. The client/server model permits multiple remote accesses to a shared testbed. This can be very important in supporting a large-scale multisite project.In this article we describe the architecture of NEST, illustrate its use, and describe some aspects of NEST implementation. We will also feature its design and provide examples of NEST applications.

Adaptive message routing for multi-dimensional networks

Abstract: An adaptive routing means and method useful for transferring messages on a number of multi-dimensional network topologies that connect distributed multi-processing systems. A plurality of processing nodes comprising processing means for processing information and router means for routing messages are connected in a multi-dimensional network (A) with an identical or redundant message passing multi-dimensional network (B) of routers being connected to network A. Each router comprises four types of channels for message passing: 1) a channel to transfer information between a router and a processor coupled to the router, 2) a channel to transfer information in an X direction, 3) a channel for the Y direction, and 4) a channel for the Z direction. This connectivity allows messages to pass between nodes within network A, between routers within network B, or between network A and network B by passing through a router. Messages are routed in networks A and B by routing first in the X dimension and then in the Y dimension. The present invention transitions between A and B networks when contention is encountered in the X or Y direction, if the appropriate Z channel is available. If an X or Y channel is not immediately granted, a request is made for the Z channel. Both the request for an X or Y channel and the request for the Z channel are maintained until one request is granted. The message is then routed on the granted channel and the other request is withdrawn. The router does not commit to routing on a particular channel until one channel is available.

Apparatus and method for detecting and eliminating call looping in a node-by-node routing network

Abstract: An apparatus and method for effectively managing a switched virtual circuit network by detecting and resolving call routing problems occurring in the routing pattern of the network is provided. Detecting the call routing problems is advantageously achieved by a first process contained in a network management center which has access to all nodes in the network and performs routing table verification for each node whenever there are changes in the routing tables caused by changes in the network, such as an addition of nodes, links and the like. Otherwise, call looping may occur during call set-up as a result of any undiscovered or uncorrected errors in one or more routing tables in the network. Detection of call loops is achieved by the first process through use of a plurality of processing modules that recognizes and excludes in their analysis of the network certain network components that can not be involved in call looping. Identified routing problems are resolved by a second process which provides alternative recommendations as to how best to modify the routing tables in the nodes of the network. A selected one of the alternative recommendations is coupled from the network management center to the nodes in the network for changing the routing tables located at the respective nodes.

Routing and flow control in high-speed wide-area networks

Abstract: The routing and flow control techniques developed for wide-area, local-area, and metropolitan-area networks are surveyed. A classification that shows the characteristics that are desirable for high-speed wide-area networks is developed. On the basis of the classification, techniques that should and should not be considered for future high-speed networks are identified. In particular, an attempt is made to determine the effect of increasing transmission rates on the routing and flow control algorithms that are used in packet-switched networks. >

An analysis of 'hot-potato' routing in a fiber optic packet switched hypercube

Abstract: Two implementations of a fiber-optic packet-switched hypercube are proposed. In the first, each directed link is implemented with a fixed wavelength laser and photodetector, and all optical transmissions are wavelength multiplexed onto one or more fibers. In the second, the electronic crosspoint matrices within the nodes are eliminated by allowing each laser to be tunable over a range of log N wavelengths. Assume that a hot potato, or deflection, routing algorithm is used; as soon as a packet is received at a node, a routing decision is made and the packet is sent out. The node attempts to send the packet towards its destination. The analysis indicates that a hypercube, hot-potato routing offers essentially optimal performance for random traffic, regardless of how large the hypercube grows, and it significantly outperforms traditional shortest-path routing with buffering and flow control. A few variations, including an algorithm which gives priority to packets closer to their destinations and one which gives priority to various classes of traffic, are also proposed and analyzed. >

Distributed dynamic routing schemes

Abstract: Schemes that do not explicitly use much information about the state of networks are briefly surveyed, with the focus on dynamic alternative routing (DAR), a simple but highly effective routing method currently planned for the British Telecom Network. State-dependent routing and how some of the methodology also has bearing on the control issue are discussed. The problem of dimensioning a network that uses dynamic routing (i.e. how much capacity is needed and where it should be put to provide an acceptable performance) is addressed. A practical example, which refers to routing in an international access network, is discussed. Some conclusions are drawn on the benefits and drawbacks of distributed routing. >

Topology distribution cost vs. efficient routing in large networks

Abstract: Routing a message in a network is efficient (in terms of weight of the path used to carry the message) when nodes know the full topology of the network. This may not be the case in large networks since a network may be composed of smaller autonomous pieces by design or by requirements on performance, with each piece having less than complete information about other pieces. We present a trade-off between the amount of topology information exchanged among these pieces and the efficiency of routing in the network. The large network that we study is a collection of networks connected by boundary nodes. Each boundary node knows the topology of its network and the connectivity of networks to each other. The question addressed here is how much topology information about each network should be distributed to other networks in order to achieve reasonably efficient routing.

Design of inter-administrative domain routing protocols

Abstract: Policy Routing (PR) is a new area of development that attempts to incorporate policy related constraints on inter-Administrative Domain (AD) communication into the route computation and forwarding of inter-AD packets.Proposals for inter-AD routing mechanisms are discussed in the context of a design space defined by three design parameters: location of routing decision (i.e., source or hop-by-hop), algorithm used (i.e., link state or distance vector), and expression of policy in topology or in link status. We conclude that an architecture based upon source routing, a link state algorithm, and policy information in the link state advertisements, is best able to address the long-term policy requirements of inter-AD routing. However, such an architecture raises several new and challenging research issues related to scaling.

Design and control of networks with dynamic nonhierarchical routing

Abstract: Dynamic routing concepts are described, and the design and control of dynamic routing networks is discussed. The vastly improved performance of the networks is illustrated with examples from operational experience. The evolution of dynamic routing with respect to several future directions is highlighted. These directions are extension to new networks and services, robust design and real-time adaptivity, and extension to interconnecting networks, including the Worldwide Intelligent Network. >

Routing in frequency-hop packet radio networks with partial-band jamming

Abstract: Describes research in adaptive, decentralized routing for frequency-hop packet radio networks with mobile partial-band jamming. A new routing technique, called least-resistance routing (LRR) is developed, and various versions of this routing method are examined. LRR uses a quantitative assessment of the interference environment at a radio to determine a resistance for that radio. This resistance is a measure of the interference the radio is likely to encounter when receiving a transmission. The investigation considers two components for the interference environment: transmissions from other radios and partial-band jamming. The resistances for each radio in a particular path are combined to form a path resistance. Packets are forwarded on the path to the destination with the least resistance. Comparisons are made between different versions of LRR and between LRR and previously developed adaptive routing techniques. It is found that LRR is an effective way for dealing with mobile jamming in a frequency-hop packet radio network. Significant increases in throughput and end-to-end probability of success are obtained by use of LRR. >

Composite routing protocols

Abstract: A novel routing protocol for computer networks is designed by combining two routing protocols that adapt to changes in the network topology. The first routing protocol is expensive to operate but yields shortest-paths in the networks; therefore, it is best used when changes in the network topology are rare. The second routing protocol is not as costly to operate, but may yield longer paths; hence, it is best used when changes in the network topology are frequent. By combining these two protocols, the resulting protocol has a wide domain of applicability that does not depend on the frequency of changes in the network topology. >

An extended least-hop distributed routing algorithm

Abstract: A routing strategy called NELHNET has been developed for networks with multiprecedence traffic and operating under dynamic traffic and topological conditions. An adaptive distributed algorithm that uses least-hop and least-hop-plus-1 routes in a table of routing vectors, as opposed to the usual table of routing scalars, is described. Current delays are passed backward and forward with the packets to allow development of expected delays to each node via all acceptable routes. The route then selected is the acceptable route with the least expected delay. For speedier recovery, a node returning to service receives the current network status from an adjoining node as soon as the link connecting them is operational. The resultant algorithms show far greater than the marginal improvements originally expected over Arpanet simulations. NELHENET strategies also permit the network to function stably under more heavily loaded conditions than do the Arpanet strategies. >

Markov decision algorithms for dynamic routing (telephone networks)

Abstract: The nature of the traffic-routing problem is described, and early studies of state-dependent routing are noted. A state-dependent scheme seeks to route each call so as to minimize the risk of blocking future calls, and thus responds to the current state of the network on the basis of certain assumptions about future traffic demands. State-dependent routing is considered as a Markov decision process. How the relative costs can be determined for the case of direct routing is shown. >

Neural Networks for Selective Vehicle Routing Heuristics

Abstract: In the vehicle routing problem (VRP), there is a collection of stops with known demands for service, and a fleet of vehicles with known capacities available to serve the stops. The problem is to assign the stops to vehicles, and specify routing sequences for each vehicle so that total distance is minimized. Many heuristic algorithms for the VRP have been developed over the last 25 years. Given a particular vehicle routing problem instance, we address here the issue of selecting which heuristic algorithm to apply to the problem. A modular system of neural networks is the knowledge base that is used to make the selection. Three types of multiple-layer neural networks are involved, and all are trained with the back-propagation learning paradigm. After training, the neural network system was applied to a collection of new problems not used in training. The system was very successful in identifying the optimal algorithm to apply to the new problems. We conclude that neural networks have considerable promise fo...

Performance issues in the design of dynamically controlled circuit-switched networks

Abstract: The evolution of circuit-switched networks is analyzed with respect to the functional innovations that allowed for new traffic controls. The technical alternatives for routing techniques and their integration with congestion and flow control are considered. The performance of dynamically controlled networks is analyzed in the framework of research done at the Centre National d'Etudes des Telecommunications (CNET) together with studies carried out in other research laboratories. Comparisons are made of dynamic routing versus fixed hierarchical routing and time-dependent routing versus adaptive routing. For adaptive routing, centralized and isolated methods are compared. The benefits of advanced control methods are summarized. >

Flow control models for multi-service networks with delayed call set up

Abstract: Admission control and routing in circuit-switched networks are investigated with two types of traffic: wideband with delayed call set up and narrowband operating in loss mode. Markov decision theory is used to construct a state-dependent routing policy. Optimality conditions for a load sharing routing are derived from the first-order Kuhn-Tucker equations. These models together with a direct routing scheme are used in a simulation study to determine the best approach for control of traffic with delayed call setup. State-dependent routing is found to be superior to direct routing and load sharing routing, although its operation is much more complex. >

The wavelength-division optical network: architectures, topologies and protocols

Abstract: Although optical-fiber waveguides can transport information at rates of several terabits per second (Tbps), this raw bandwidth cannot be easily harnessed, because digital electronic circuits are not capable of transmitting or receiving information at such high rates. The Wavelength-Division Optical Network (WON) is a multichannel, multihop, store-and-forward, packet-switching network that takes advantage of the enormous bandwidth of lightwave technology by multiplexing several different, noninterfering wavelengths of light onto a single optical fiber. Such wavelength-division multiplexing (WDM) allows the creation of a large number of high-speed channels on an optical fiber. The WON, which is constructed from multitransceiver stations quasistatically tuned to the WDM channels, provides excellent throughput at a low cost, compared to other proposed networks. The WON is unique among networks because it possesses both a physical topology and a virtual topology, and its virtual topology, which defines the logical interconnection of stations, may be specified independently of its physical topology. Furthermore, when wavelength-agile transceivers are used, the WON's virtual topology can be redefined at any point during its lifetime, which makes it possible to adapt the network to evolving conditions such as changes in the traffic load. This work addresses the problems of designing the WON. The implementation of a WON requires the solution of several interrelated problems, including the design of its cable plant, its physical topology, its virtual topology, and its routing procedures. The goal of cable-plant and physical-topology design is to provide a power-efficient optical-signal distribution system with the lowest possible cost. We develop and demonstrate techniques for designing minimum-cost physical topologies for the WON. Given a specific physical topology and traffic requirements, the goal of virtual-topology and routing-protocol design is to select a routing procedure and assign stations to WDM channels so that the WON's performance is optimized when the routing protocol is used with the virtual topology. We adapt the well-known simulated annealing and genetic algorithms for use in optimizing the virtual topology of the WON to achieve optimum performance. We also develop a technique called, detour routing, that efficiently delivers packets when stations have as few as one packet buffer per transmitter.

Distributed and fail-safe routing algorithms in toroidal-based metropolitan area networks

Abstract: A two-dimensional toroidal network is simply a rectangular mesh where opposite nodes on the left and right boundaries are connected to each other and opposite nodes on the upper and lower boundaries are also connected to each other. Examples of toroidal based metropolitan area networks are HR 4 -NET and Manhattan Street Network (MSN). The original routing algorithm for HR 4 -NET proposed by Borgonovo and Cadorin, however, does not direct packets through shortest paths. This paper presents shortest path routing algorithms for HR 4 -NET, which are distributed and fail-safe. These algorithms can also be applied to multiple traffic types. Simple routing rules that use of the regular structure of the network are compared to MSN.

Neural network controller for adaptive routing in survivable communications networks

Abstract: An isolated routing algorithm for adaptive dynamic routing in communications networks that is based on a neural network approach has been developed. A neural network is located within each site of a communications network, and it uses the patterns of incoming traffic to maintain and dynamically update an internal representation of the global topology of the communications network. The information stored in the neural network models is updated using various routing paradigms, including Hebbian learning. The scheme has been implemented in a software simulation running on a Sun workstation

Decentralized routing, teams and neural networks in communications

Abstract: A communication network with stochastic input flows is considered. The nodes which route the traffic are required: (i) to react instantaneously to the variations of their incoming flows so as to minimize an aggregate transmission cost, and (ii) to compute or adapt their routing strategies online on the basis of the measured values of the incoming flows and of some local information. Owing to the first requirement, the routing nodes must be considered as the cooperating decision makers of a team organization. The second requirement calls for a computationally distributed algorithm. This fact and the intractability, under general conditions, of team functional optimization problems were the reasons to assign each routing node a multilayer feedforward neural network, which generates the routing variables. For these neural networks the stochastic input flows play the role of training patterns. The weights of the routing neural networks are then adjusted by means of an efficient algorithm based on backpropagation and stochastic approximation. >

Rearrangeability of shuffle-exchange networks

Abstract: A proof for the rearrangeability of (2n-1)-stage shuffle-exchange networks with N=2/sup n/ inputs is given. The proof makes use of the notion of balanced matrices for representing passable permutations through a shuffle-exchange network. Because the proof is not constructive, it does not lead to a routing algorithm directly. Therefore, a heuristic algorithm is provided for routing arbitrary permutations on the (2n-1)-stage shuffle-exchange network. A new proof for the rearrangeability of the (2n-1) stage reduced Omega /sub N/ Omega /sub N//sup -1/ network is also given, and a routing algorithm using precomputed digit-controlled routing tags is presented. >

A deadlock free routing algorithm with network size independent buffering space

Abstract: The purpose of this paper is to describe the theory behind a correct routing function suitable for parallel machines composed of networks of asynchronous processors. We propose a new deadlock free routing function which avoids the drawbacks of existing methods based on buffers ordering. The algorithm is based on a protocol which insures the correct delivery of messages at their destination in networks of even degree. A few restrictions are considered for the calculus of routes in the network. Under such restrictions, messages are routed through the shortest paths and never cross the same route. The buffer space required is independent of the size of the network. The routing function gives all the valid paths between any two nodes, thus adaptive routing can be envisaged in order to achieve load balancing.

Adaptive window flow control and learning algorithms for adaptive routing in data networks

Abstract: We present a new adaptive flow control algorithm together with learning routing algorithms.The key performance measure in both algorithms is packet delay. Window adjustment and route selection are based on delay measurements. Simulation results have shown the superiority of the new scheme over existing algorithms.

An approach to protocol complementation for internetworking

Abstract: To solve the protocol complementation problem step by step, the authors present three algorithms. They include transformation of the problem into a protocol synthesis problem, synthesis of a tree protocol, and construction of a conventional protocol for the virtual layer. One advantage of this approach is that it makes it possible to use existing protocol synthesis techniques. Another advantage is that, because this approach considers all the transition sequences in the intended interworking function between the original protocols, it can solve protocol internetworking problems which cannot be solved using protocol conversion or protocol overlapping techniques. >

Minimal order loop-free routing strategy

Abstract: A multiorder routing strategy is developed which is loop-free even in the presence of link/node failures. Unlike most conventional methods in which the same routing strategy is applied indiscriminately to all nodes in the network, nodes under this proposal may adopt different routing strategies according to the network structure. Formulas are developed to determine the minimal order of routing strategy for each node to eliminate looping completely. A systematic procedure for striking a compromise between the operational overhead and network adaptability is proposed. Several illustrative examples are presented. >

High-speed propagation of link status routing control information

Abstract: A link status routing algorithm required each node to know the current status of all the links in the network. Nodes use a link status update protocol that helps in keeping the database at each node up-to-date. The authors describe a link status update protocol designed for a highspeed network. The protocol uses the best-effort model of packet delivery, but is fault-tolerant. It uses an algorithm for fast propagation of link status updates that is optimized for the expected case when no update packets are lost, and no link or node failures occur. The protocol uses a separate mechanism to detect and recover from errors caused by loss of updates and failure of nodes or links. >