Practical OSPF traffic engineering

Open Shortest Path First (OSPF) traffic engineering (TE) is intended to bring long-awaited traffic management capabilities into IP networks, which still rely on today's prevailing routing protocols: OSPF or IS-IS. In OSPF, traffic is forwarded along, and split equally between, equal cost shortest paths. In this letter, we formulate the basic requirements placed on a practical TE architecture built on top of OSPF and present a theoretical framework meeting these requirements of practicality. The main contribution of our work comes from the recognition that coupled with an instance of the maximum throughput problem there exists a related inverse shortest-path problem yielding optimal OSPF link weights.     

Optimal configuration of OSPF aggregates

Open Shortest Path First (OSPF) is a popular protocol for routing within an autonomous system (AS) domain. In order to scale for large networks containing hundreds and thousands of subnets, OSPF supports a two-level hierarchical routing scheme through the use of OSPF areas. Subnet addresses within an area are aggregated, and this aggregation is a crucial requirement for scaling OSPF to large AS domains, as it results in significant reductions in routing table sizes, smaller link-state databases, and less network traffic to synchronize the router link-state databases. On the other hand, address aggregation also implies loss of information about the length of the shortest path to each subnet, which in turn, can lead to suboptimal routing. We address the important practical problem of configuring OSPF aggregates to minimize the error in OSPF shortest-path computations due to subnet aggregation. We first develop an optimal dynamic programming algorithm that, given an upper bound k on the number of aggregates to be advertised and a weight assignment function for the aggregates, computes the k aggregates that result in the minimum cumulative error in the shortest-path computations for all source-destination subnet pairs. Subsequently, we tackle the problem of assigning weights to OSPF aggregates such that the cumulative error in the computed shortest paths is minimized. We demonstrate that, while for certain special cases (e.g., unweighted cumulative error) efficient optimal algorithms for the weight assignment problem can be devised, the general problem itself is NP-hard. Consequently, we have to rely on search heuristics to solve the weight assignment problem. To the best of our knowledge, our work is the first to address the algorithmic issues underlying the configuration of OSPF aggregates and to propose efficient configuration algorithms that are provably optimal for many practical scenarios.     

Dissemination of routing information in broadcast networks: OSPFversus 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     

Two phase load balanced routing using OSPF

The Internet traffic is growing, and its nature changes because of new applications. Multimedia applications require bandwidth reservations that were not needed initially when the file transfers dominated the Internet. P2P applications are making traffic patterns impossible to predict, and the traffic loads generated at nodes need to be routed regardless of the traffic pattern. When the guaranteed node traffic loads are known, bandwidth reservations can be made simple as will be explained in the paper. The shortest path routing (SPR) protocols used on the Internet today do not maximize the guaranteed node traffic loads, and do not provide scalable and fast bandwidth reservations. Load balancing can improve the network throughput for arbitrary traffic pattern. In this paper we analyze and implement a routing protocol that is based on load balancing and a commonly used shortest path routing protocol, and is, consequently, termed as LB-SPR. LB-SPR is optimized for an arbitrary traffic pattern, i.e. it does not assume a particular traffic matrix. Optimization assumes only the weights assigned to the network nodes according to their estimated demands. It will be shown that the optimized routing achieves the throughputs which are significantly higher than those provided by the currently used SPR protocols, such as OSPF or RIP. Importantly, LB-SPR calculates the guaranteed traffic loads and so allows fast autonomic bandwidth reservations which are the key for the successful support of triple-play applications, including video and audio applications that require high QoS. An actual modification of the TCP/IP stack that includes LBSPR is also described. Using the signaling mechanisms of the OSPF protocol, the information needed to perform the routing optimization is automatically distributed among the network nodes whenever the network topology changes. The LB-SPR implementation is validated on a sample network using a popular virtualization tool - Xen.     

A generalized service deployment framework for OSPF networks using multi‐topology routing: Modeling and methodology

The exponential growth of various applications requires deploying an ever‐growing number of network services. A generalized service deployment framework for Open Shortest Path First (OSPF) networks is proposed in this paper. The framework includes placing programmable routers, distributing different types of services on these routers, and leading traffic flow through them according to the predetermined sequence order requirement. However, it is not possible to direct all the traffic flows through the required service nodes along the shortest path with a single and suitable set of link weights. To address the issue, multiple topology routing (MTR) technique is incorporated to have various logical topologies with multiple sets of link weights. Correspondingly, the problem of jointly optimizing Placement of programmable routers, Distribution of different types of services among these routers, and Link Weights setting based on MTR (shortened to PD‐LW‐MTR) and its mixed integer linear programming formulation are presented in this paper. A novel decomposition algorithm is also proposed to address this problem efficiently. Experiment results validate the correctness and feasibility of our algorithm. It is also shown that the optimization algorithm can obtain near‐optimal solution and just only a few logical topologies over multiple sets of link weights are necessary for traffic flows to guarantee service order requirements.     

Performance of new link state advertisement mechanisms in routing protocols with traffic engineering extensions

The prevalent use of best-effort topology driven IP routing protocols with shortest path calculations can often lead to serious imbalance of packet traffic distribution when least cost paths converge on the same set of links, leading to unacceptable delays or packet loss even in the presence of feasible paths over less utilized links. Recently proposed enhancements to common routing protocols are promising to overcome such shortcomings by providing the means to distribute link state information that is more pertinent to traffic engineering in routed networks. This article presents several key results on the performance of the recently proposed OSPF-TE, with particular emphasis on OSPF-TE protocol traffic overhead and the impact of new link state advertisement triggering mechanisms on traffic-engineered routing accuracy.     

Performance analysis of multicast routing and wavelength assignment protocol with dynamic traffic grooming in WDM networks

The need for on‐demand provisioning of wavelength‐routed channels with service‐differentiated offerings within the transport layer has become more essential because of the recent emergence of high bit rate Internet protocol (IP) network applications. Diverse optical transport network architectures have been proposed to achieve the above requirements. This approach is determined by fundamental advances in wavelength division multiplexing (WDM) technologies. Because of the availability of ultra long‐reach transport and all‐optical switching, the deployment of all‐optical networks has been made possible. The concurrent transmission of multiple streams of data with the assistance of special properties of fiber optics is called WDM. The WDM network provides the capability of transferring huge amounts of data at high speeds by the users over large distances. There are several network applications that require the support of QoS multicast, such as multimedia conferencing systems, video‐on‐demand systems, real‐time control systems, etc. In a WDM network, the route decision and wavelength assignment of lightpath connections are based mainly on the routing and wavelength assignment (RWA). The multicast RWA's task is to maximize the number of multicast groups admitted or minimize the call‐blocking probability. The dynamic traffic‐grooming problem in wavelength‐routed networks is generally a two‐layered routing problem in which traffic connections are routed over lightpaths in the virtual topology layer and lightpaths are routed over physical links in the physical topology layer. In this paper, a multicast RWA protocol for capacity improvement in WDM networks is designed. In the wavelength assignment technique, paths from the source node to each of the destination nodes and the potential paths are divided into fragments by the junction nodes and these junction nodes have the wavelength conversion capability. By using the concept of fragmentation and grouping, the proposed scheme can be generally applied for the wavelength assignment of multicast in WDM networks. An optimized dynamic traffic grooming algorithm is also developed to address the traffic grooming problem in mesh networks in the multicast scenario for maximizing the resource utilization and minimizing the blocking probability. Copyright © 2011 John Wiley & Sons, Ltd.     

An OSPF topology server: design and evaluation

In large scale, operational Internet protocol networks, creating timely, accurate and network-wide views of the intradomain topology is a fundamental problem. Topical network backbones consist of hundreds of routers, which establish routing adjacencies with one another through static configuration and dynamic routing protocols, such as open shortest path first (OSPF). We describe the design of an OSPF topology server which tracks intradomain topology, by passively and safely listening into OSPFs reliable flooding mechanism, or by pushing and pulling information from the routers via the simple network management protocol. We provide a detailed evaluation and comparison of the two approaches in terms of operational issues, reliability and timeliness of information     

Achieving near-optimal traffic engineering solutions for current OSPF/IS-IS networks

Traffic engineering aims to distribute traffic so as to "optimize" some performance criterion. This optimal distribution of traffic depends on both the routing protocol and the forwarding mechanisms in use in the network. In IP networks running the OSPF or IS-IS protocols, routing is over shortest paths, and forwarding mechanisms distribute traffic "uniformly" over equal cost shortest paths. These constraints often make achieving an optimal distribution of traffic impossible. In this paper, we propose and evaluate an approach that can realize near optimal traffic distribution without changes to routing protocols and forwarding mechanisms. In addition, we explore the tradeoff that exists between performance and the configuration overhead that our solution requires. The paper's contributions are in formulating and evaluating an approach to traffic engineering in IP networks that achieves near-optimal performance while preserving the existing infrastructure.     

Calcul des métriques de routage pour Internet

In spite of the development of Internet networks and the important volume of literature dealing with Internet routing, many fundamental topics were not addressed. Traffic is, in principle, routed through shortest paths, in sense of a set of link weights (a metric). These weights do not necessarily have a physical significance and could be modified by the network administrator to change the routing policy and the network cost. In this paper, we give precise answers for the following questions: 1/ Given a network topology, is there a metric such that, first, the shortest path between any pair of vertices is unique and, second, every link belongs to at least one shortest path ? 2/ How can we compute such a metric ? 3/ Can we choose a metric satisfying these constraints and whose values are small integers ? 4/ If the routers of the network have differents functions and caracteristics, is it possibe to determine a metric which allows to route traffic, taking into account these heteregeneous caracteristics ? 5/ If some routing paths are seleceted due to technical or economical reasons, can we find a metric enforcing this given routing policy ? 6/ If this is not possible, what should we do to compute a metric that is as close as possible to the selected routing paths ?     

Preconfiguring IP-over-Optical Networks to Handle Router Failures and Unpredictable Traffic

We consider the realization of traffic-oblivious routing in IP-over-optical networks where routers are interconnected over a switched optical backbone. The traffic-oblivious routing we consider is a scheme where incoming traffic is first distributed in a preset manner to a set of intermediate nodes. The traffic is then routed from the intermediate nodes to the final destination. This splitting of the routing into two phases simplifies network configuration significantly. In implementing this scheme, the first and second phase paths are realized at the optical layer with router packet grooming at a single intermediate node only. Given this unreliability of routers, we consider how two-phase routing in IP-over-optical networks can be made resilient against router node failures. We propose two different schemes for provisioning the optical layer to handle router node failures-one that is failure node independent and static, and the other that is failure node dependent and dynamic We develop linear programming formulations for both schemes and a fast combinatorial algorithm for the second scheme so as to maximize network throughput. In each case, we determine (i) the optimal distribution of traffic to various intermediate routers for both normal (no-failure) and failure conditions, and (ii) provisioning of optical layer circuits to provide the needed inter-router links. We evaluate the performance of the two router failure protection schemes and compare it with that of unprotected routing     

基于可重构网络的节能方法的研究

针对当前IP网络的节能算法实用性不强的问题,根据可重构网络路由配置由中心服务器统一管理的架构特点,基于网络中的OSPF协议探测结果,提出了可重构网络下的节能方法。该方法首先运用改进的OSPF协议的路由算法定位出可被关闭的候选链路集合,接着应用多商品流模型重映射该集合中某些链路的流量到其他的物理路径,从而能够关闭候选链路集合中的空负荷链路实现网络的节能。通过实验模拟验证了该算法的节能效益,并给出了可重构网络中的节能算法与认可度极高的节能方法——GreenTE异同点。     

MPLS-based satellite constellation networks

Nongeostationary satellite constellations with intersatellite links are a challenge for networking due to their continuously changing topology. In order to make maximal use of the network's capacities, special attention has to be paid to routing and traffic engineering. Multiprotocol label switching (MPLS) as underlying protocol is an interesting candidate for this task since it offers many possibilities to exert influence on traffic flows and supports today's dominating Internet protocol traffic very well. This paper describes a general MPLS-based networking concept for satellite networks and discusses different scenarios considering the particularities and constraints of the dynamic topology. Functional elements of MPLS like ingress, egress, or core routers have to be mapped onto the physical entities of the network and prerequisites for traffic engineering are discussed. Routing and rerouting of paths is of key interest since this affects route computation effort and routing performance. Thus, an analytical estimation of routing effort is deduced and numerical and simulation results are presented.     

A novel robust routing algorithm for multi-granularity connection requests in wavelength division multiplexing mesh networks

In this paper, we propose a novel robust routing algorithm based on Valiant load-balancing under the model of polyhedral uncertainty (i.e., hose uncertainty model) for WDM (wavelength division multiplexing) mesh networks. Valiant load-balanced robust routing algorithm constructs the stable virtual topology on which any traffic patterns under the hose uncertainty model can be efficiently routed. Considering there are multi-granularity connection requests in WDM mesh networks, we propose the method called hose-model separation to solve the problem for the proposed algorithm. Our goal is to minimize total network cost when constructing the stable virtual topology that assures robust routing for the hose model in WDM mesh networks. A mathematical formulation (integer linear programming, ILP) about Valiant load-balanced robust routing algorithm is presented. Two fast heuristic approaches are also proposed and evaluated. We compare the network throughput of the virtual topology constructed by the proposed algorithm with that of the traditional traffic grooming algorithm under the same total network cost by computer simulation.     

A routing architecture for mobile integrated services networks

A drawback of the conventional Internet routing architecture is that its route computation and packet forwarding mechanisms are poorly integrated with congestion control mechanisms. Any datagram offered to the network is accepted; routers forward packets on a best-effort basis and react to congestion only after the network resources have already been wasted. A number of proposals improve on this to support multimedia applications; a promising example is the Integrated Services Packet Network (ISPN) architecture. However, these proposals are oriented to networks with fairly static topologies and rely on the same conventional Internet routing protocols to operate. This paper presents a routing architecture for mobile integrated services networks in which network nodes (routers) can move constantly while providing end-to-end performance guarantees. In the proposed connectionless routing architecture, packets are individually routed towards their destinations on a hop by hop basis. A packet intended for a given destination is allowed to enter the network if and only if there is at least one path of routers with enough resources to ensure its delivery within a finite time. Once a packet is accepted into the network, it is delivered to its destination, unless resource failures prevent it. Each router reserves resources for each active destination, rather than for each source–destination session, and forwards a received packet along one of multiple loop-free paths towards the destination. The resources and available paths for each destination are updated to adapt to congestion and topology changes. This mechanism could be extended to aggregate dissimilar flows as well. This revised version was published online in June 2006 with corrections to the Cover Date.     

RATES: a server for MPLS traffic engineering

It has been suggested that one of the most significant reasons for multiprotocol label switching (MPLS) network deployment is network traffic engineering. The goal of traffic engineering is to make the best use of the network infrastructure, and this is facilitates by the explicit routing feature of MPLS, which allows many of the shortcomings associated with current IP routing schemes to be addressed. This article describes a software system called Routing and Traffic Engineering Server (RATES) developed for MPLS traffic engineering. It also describes some new routing ideas incorporated in RATES for MPLS explicit path selection. The RATES implementation consists of a policy and flow database, a browser-based interface for policy definition and entering resource provisioning requests, and a Common Open Policy Service protocol server-client implementation for communicating paths and resource information to edge routers. RATES also uses the OSPF topology database for dynamically obtaining link state information. RATES can set up bandwidth-guaranteed label-switched (LSPs) between specified ingress-egress pairs. The path selection for LSPs is on a new minimum-interference routing algorithm aimed at making the best use of network infrastructure in an online environment where LSP requests arrive one by one with no a priori information about future requests. Although developed for an MPLS application, the RATES implementation has many similarities in components to an intradomain differentiated services bandwidth broker     

SMORT: Scalable multipath on-demand routing for mobile ad hoc networks

Increasing popularity and availability of portable wireless devices, which constitute mobile ad hoc networks, calls for scalable ad hoc routing protocols. On-demand routing protocols adapt well with dynamic topologies of ad hoc networks, because of their lower control overhead and quick response to route breaks. But, as the size of the network increases, these protocols cease to perform due to large routing overhead generated while repairing route breaks. We propose a multipath on-demand routing protocol (SMORT), which reduces the routing overhead incurred in recovering from route breaks, by using secondary paths. SMORT computes fail-safe multiple paths, which provide all the intermediate nodes on the primary path with multiple routes (if exists) to destination. Exhaustive simulations using GloMoSim with large networks (2000 nodes) confirm that SMORT is scalable, and performs better even at higher mobility and traffic loads, when compared to the disjoint multipath routing protocol (DMRP) and ad hoc on-demand distance vector (AODV) routing protocol.     

Flow Routing and its Performance Analysis in Optical IP Networks

Optical packet-switching networks deploying buffering, wavelength conversion and multi-path routing have been extensively studied in recent years to provide high capacity transport for Internet traffic. However due to packet-based routing and switching, such a network could result in significant disorder and delay variation of packets when they are received by end users, thus increasing the burstiness of the Internet traffic and causing higher-layer protocol to malfunction. This paper addresses a novel routing and switching method for optical IP networks — flow routing, and its facilitating protocol. Flow routing deals with packet-flows to reduce flow corruption due to packet out-of-order, delay variation and packet loss, without using complicate control mechanism. Detailed performance analysis is given for output-buffered optical routers adopting flow routing. Two flow-oriented discarding techniques, i.e., flow discard (FD) and early flow discard (EFD), are discussed. Compared with optical packet-switching routers, a remarkable improvement of good-throughput is obtained in the optical flow-routers, especially under high congestion periods. We conclude that EFD behaves as a robust technique, which is more tolerant than FD to the change of traffic and transmission system factors.     

Logical topology design for IP rerouting: ASONs versus static OTNs

IP-based backbone networks are gradually moving to a network model consisting of high-speed routers that are flexibly interconnected by a mesh of light paths set up by an optical transport network that consists of wavelength division multiplexing (WDM) links and optical cross-connects. In such a model, the generalized MPLS protocol suite could provide the IP centric control plane component that will be used to deliver rapid and dynamic circuit provisioning of end-to-end optical light paths between the routers. This is called an automatic switched optical (transport) network (ASON). An ASON enables reconfiguration of the logical IP topology by setting up and tearing down light paths. This allows to up- or downgrade link capacities during a router failure to the capacities needed by the new routing of the affected traffic. Such survivability against (single) IP router failures is cost-effective, as capacity to the IP layer can be provided flexibly when necessary. We present and investigate a logical topology optimization problem that minimizes the total amount or cost of the needed resources (interfaces, wavelengths, WDM line-systems, amplifiers, etc.) in both the IP and the optical layer. A novel optimization aspect in this problem is the possibility, as a result of the ASON, to reuse the physical resources (like interface cards and WDM line-systems) over the different network states (the failure-free and all the router failure scenarios). We devised a simple optimization strategy to investigate the cost of the ASON approach and compare it with other schemes that survive single router failures.