Locally Restorable Routing of Highly Variable Traffic

Two-phase routing, where traffic is first distributed to intermediate nodes before being routed to the final destination, has been recently proposed for handling widely fluctuating traffic without the need to adapt network routing to changing traffic. Preconfiguring the network in a traffic independent manner using two-phase routing simplifies network operation considerably. In this paper, we extend this routing scheme by providing resiliency against link failures through fast restoration along link backup detours. We view this as important progress towards adding carrier-class reliability to the robustness of the scheme so as to facilitate its future deployment in Internet Service Provider (ISP) networks. On the theoretical side, the main contribution of the paper is the development of linear programming based and fast combinatorial algorithms for two-phase routing with link restoration so as to minimize the maximum utilization of any link in the network, or equivalently, maximize the throughput. The algorithms developed are fully polynomial time approximation schemes (FPTAS)-for any given isin > 0, an FPTAS guarantees a solution that is within a (1 + isin)-factor of the optimum and runs in time polynomial in the input size and 1/isin. To the best of our knowledge, this is the first work in the literature that considers making the scheme resilient to link failures through preprovisioned fast restoration mechanisms. We evaluate the performance of link restoration (in terms of throughput) and compare it with that of unprotected routing. For our experiments, we use actual ISP network topologies collected for the Rocketfuel project and three research network topologies.     

Guaranteed Performance Routing of Unpredictable Traffic With Fast Path Restoration

Two-phase routing, where traffic is first distributed to intermediate nodes before being routed to the final destination, has been recently proposed for handling widely fluctuating traffic without the need to adapt network routing to changing traffic. Preconfiguring the network in a traffic-independent manner using two-phase routing simplifies network operation considerably. In this paper, we extend this routing scheme by providing resiliency against link failures through fast path restoration along disjoint end-to-end backup paths. We view this as important progress toward adding carrier-class reliability to the robustness of the scheme so as to facilitate its future deployment in Internet service provider (ISP) networks. On the theoretical side, the main contribution of the paper is the development of linear-programming-based and fast combinatorial algorithms for two-phase routing with fast path restoration so as to minimize the maximum utilization of any link in the network, or equivalently, maximize the throughput. The algorithms developed are fully polynomial time approximation schemes (FPTAS)-for any given epsiv > 0, an FPTAS guarantees a solution that is within a (1+epsiv)-factor of the optimum and runs in time polynomial in the input size and [ 1/(relax epsiv)]. To the best of our knowledge, this is the first work in the literature that considers making the scheme resilient to link failures through preprovisioned fast restoration mechanisms. We evaluate the performance of fast path restoration (in terms of throughput) and compare it to that of unprotected routing. For our experiments, we use actual ISP network topologies collected for the Rocketfuel project and three research network topologies.     

Maze Routing Steiner Trees With Delay Versus Wire Length Tradeoff

In this paper, we address the problem of generating good topologies of rectilinear Steiner trees using path search algorithms. Various techniques have been applied in order to achieve acceptable run times on a Maze Router that builds Steiner trees. A biasing technique proposed for wire length improvement, produces trees that are within 2% from optimal topologies in average. By introducing a sharing factor and a path-length factor we show how to trade-off wire length for delay. Experimental results show that our algorithm generates topologies with better delay compared to state of the art heuristics for Steiner trees, such as AHHK (from 26% to 40%) and P-Trees (from 1% to 30% and from 6% to 21% in the presence of blockages) while keeping the properties of a routing algorithm. An important motivation for this work lies in the fact that it can be used for estimation in the early stages as well as for actual routing, thereby improving the convergence and timing closure of the design significantly. We also provide some valuable theoretical background and insights on delay optimization and on how it relates to our maze router implementation.      

Lord of the Links: A Framework for Discovering Missing Links in the Internet Topology

The topology of the Internet at the autonomous system (AS) level is not yet fully discovered despite significant research activity. The community still does not know how many links are missing, where these links are and finally, whether the missing links will change our conceptual model of the Internet topology. An accurate and complete model of the topology would be important for protocol design, performance evaluation and analyses. The goal of our work is to develop methodologies and tools to identify and validate such missing links between ASes. In this work, we develop several methods and identify a significant number of missing links, particularly of the peer-to-peer type. Interestingly, most of the missing AS links that we find exist as peer-to-peer links at the Internet exchange points (IXPs). First, in more detail, we provide a large-scale comprehensive synthesis of the available sources of information. We cross-validate and compare BGP routing tables, Internet routing registries, and traceroute data, while we extract significant new information from the less-studied Internet exchange points (IXPs). We identify 40% more edges and approximately 300% more peer-to-peer edges compared to commonly used data sets. All of these edges have been verified by either BGP tables or traceroute. Second, we identify properties of the new edges and quantify their effects on important topological properties. Given the new peer-to-peer edges, we find that for some ASes more than 50% of their paths stop going through their ISPs assuming policy-aware routing. A surprising observation is that the degree of an AS may be a poor indicator of which ASes it will peer with.     

Cartographie distribuée du cœur de l’Internet

The study of the Internet topology allows us to discover properties that can be beneficial to the performances of network protocols and applications. Thus, Internet mapping is very useful to simulation software focusing on network protocols. Unfortunately Internet mapping has two major drawbacks. First it takes a lot of time to be carried out and second it is often incomplete. To solve these two problems, we have developed a fast mapping software whose aim is to map the heart of the Internet as fast as possible with the highest attainable precision. In this paper, we describe our software and evaluate its performances compared to an existing and freely available mapping software. We assess the completeness of the router level maps by creating overlays with an autonomous system topology. We also assess its use inIpv6 and the evolution of its performances inIpv4 when increasing the size of the input parameter set. We conclude with a detailed study on the delay of the paths and links in the Internet.     

Efficient visualization of large routing topologies

As the Internet grows in size and complexity, network managers face a significant challenge in trying to understand the behaviour of routing protocols in large networks. In this paper, we present a tool called VLNT (visualizing large network topologies), which helps network managers to analyse complex routing topologies. A key contribution of our system is a novel hybrid layout algorithm, which significantly reduces the computation time required to layout large network topologies in comparison to conventional layout approaches. In addition our algorithm includes a novel termination criterion that avoids unnecessary iterations when optimizing the network layout. We demonstrate how the visualization features of VLNT can be used to analyse and improve BGP routing topologies, and provide examples using real‐life routing data. Copyright © 2004 John Wiley & Sons, Ltd.     

Impact of Hot-Potato Routing Changes in IP Networks

Despite the architectural separation between intradomain and interdomain routing in the Internet, intradomain protocols do influence the path-selection process in the Border Gateway Protocol (BGP). When choosing between multiple equally-good BGP routes, a router selects the one with the closest egress point, based on the intradomain path cost. Under such hot-potato routing, an intradomain event can trigger BGP routing changes. To characterize the influence of hot-potato routing, we propose a technique for associating BGP routing changes with events visible in the intradomain protocol, and apply our algorithm to a tier-1 ISP backbone network. We show that (i) BGP updates can lag 60 seconds or more behind the intradomain event; (ii) the number of BGP path changes triggered by hot-potato routing has a nearly uniform distribution across destination prefixes; and (iii) the fraction of BGP messages triggered by intradomain changes varies significantly across time and router locations. We show that hot-potato routing changes lead to longer delays in forwarding-plane convergence, shifts in the flow of traffic to neighboring domains, extra externally-visible BGP update messages, and inaccuracies in Internet performance measurements.      

An optimal dynamic resources partitioning auction model for virtual private networks

In this paper, we consider the problem of optimizing the Internet Service Provider (ISP) profit by providing a periodic Dynamic Partitioning (DP) model for utilizing network resources in the context of Virtual Private Networks (VPN). In literature, Complete Sharing (CS), Complete Partitioning (CP), and Bandwidth Borrowing (BR) techniques have been proposed for resource allocation where the following limitations can be noticed: VPN operators can exaggerate about their required resources, resources might be underutilized, and optimal bandwidth utilization is not guaranteed. To overcome the above limitations, we propose to dynamically partition the resources over different QoS classes through periodic auctions that can reduce the reasoning of exaggeration and maximize the ISP profit. Thus, we formulate our problem based on the Integer Linear Programming (ILP) that allows us to maximize the ISP profit and provides the optimal: (1) set of profitable VPN connections, (2) bandwidth division of each network link among QoS classes, and (3) routing scheme for the accepted demand. Furthermore, the proposed ILP model allows us to study the sensitivity of the ISP profit to a targeted revenue objective.     

Performance Preserving Topological Downscaling of Internet-Like Networks

The Internet is a large, heterogeneous system operating at very high speeds and consisting of a large number of users. Researchers use a suite of tools and techniques in order to understand the performance of complex networks like the Internet: measurements, simulations, and deployments on small to medium-scale testbeds. This work considers a novel addition to this suite: a class of methods to scale down the topology of the Internet that enables researchers to create and observe a smaller replica, and extrapolate its performance to the expected performance of the larger Internet. This is complementary to the work of Psounis, 2003, where the authors presented a way to scale down the Internet in time, by creating a slower replica of the original system. The key insight that we leverage in this work is that only the congested links along the path of each flow introduce sizable queueing delays and dependencies among flows. Hence, one might hope that the network properties can be captured by a topology that consists of the congested links only. Using extensive simulations with transmission control protocol (TCP) traffic and theoretical analysis, we show that it is possible to achieve this kind of performance scaling even on topologies the size of the CENIC backbone (that provides Internet access to higher education institutions in California). We also show that simulating a scaled topology can be up to two orders of magnitude faster than simulating the original topology     

Junction-Based Geographic Routing Algorithm for Vehicular Ad hoc Networks

Vehicular Ad hoc Networks have attracted the interest of the scientific community, since many issues remain open, especially in the research area of routing techniques. In this work we propose a new position-based routing algorithm called Junction-Based Routing. The algorithm makes use of selective greedy forwarding up to the node that is located at a junction and is closer to the destination. If a local optimum is reached, a recovery strategy is applied, the key point of which is our proposed minimum angle method. We evaluate the performance of our routing protocol in real city topology. The simulated scenarios use obstacle modelling and several different Physical layer settings. Simulation results show that our proposal achieves superior performance compared to the well-known Greedy Perimeter Coordinator Routing algorithm.     

Network topologies: inference, modeling, and generation

Accurate measurement, inference and modeling techniques are fundamental to Internet topology research. Spatial analysis of the Internet is needed to develop network planning, optimal routing algorithms, and failure detection measures. A first step toward achieving such goals is the availability of network topologies at different levels of granularity, facilitating realistic simulations of new Internet systems. The main objective of this survey is to familiarize the reader with research on network topology over the past decade. We study techniques for inference, modeling, and generation of the Internet topology at both the router and administrative levels. We also compare the mathematical models assigned to various topologies and the generation tools based on them. We conclude with a look at emerging areas of research and potential future research directions.     

Internet routing instability

This paper examines the network interdomain routing information exchanged between backbone service providers at the major US public Internet exchange points. Internet routing instability, or the rapid fluctuation of network reachability information, is an important problem currently facing the Internet engineering community. High levels of network instability can lead to packet loss, increased network latency and time to convergence. At the extreme, high levels of routing instability have led to the loss of internal connectivity in wide-area, national networks. We describe several unexpected trends in routing instability, and examine a number of anomalies and pathologies observed in the exchange of inter-domain routing information. The analysis in this paper is based on data collected from border gateway protocol (BGP) routing messages generated by border routers at five of the Internet core's public exchange points during a nine month period. We show that the volume of these routing updates is several orders of magnitude more than expected and that the majority of this routing information is redundant, or pathological. Furthermore, our analysis reveals several unexpected trends and ill-behaved systematic properties in Internet routing. We finally posit a number of explanations for these anomalies and evaluate their potential impact on the Internet infrastructure     

Practical Beacon Placement for Link Monitoring Using Network Tomography

Recent interest in using tomography for network monitoring has motivated the issue of whether it is possible to use only a small number of probing nodes (beacons) for monitoring all edges of a network in the presence of dynamic routing. Past work has shown that minimizing the number of beacons is NP-hard, and has provided approximate solutions that may be fairly suboptimal. In this paper, we use a two-pronged approach to compute an efficient beacon set: 1) we formulate the need for, and design algorithms for, computing the set of edges that can be monitored by a beacon under all possible routing states and 2) we minimize the number of beacons used to monitor all network edges. We show that the latter problem is NP-complete and use various approximate placement algorithm that yields beacon sets of sizes within 1+ln(|E|) of the optimal solution, where E is the set of edges to be monitored. Beacon set computations for several Rocketfuel Internet service provider topologies indicate that our algorithms may reduce the number of beacons yielded by past solutions by more than 50% and are, in most cases, close to optimal     

Delayed Internet routing convergence

This paper examines the latency in Internet path failure, failover, and repair due to the convergence properties of interdomain routing. Unlike circuit-switched paths which exhibit failover on the order of milliseconds, our experimental measurements show that interdomain routers in the packet-switched Internet may take tens of minutes to reach a consistent view of the network topology after a fault. These delays stem from temporary routing table fluctuations formed during the operation of the border gateway protocol (BGP) path selection process on the Internet backbone routers. During these periods of delayed convergence, we show that end-to-end Internet paths will experience intermittent loss of connectivity, as well as increased packet loss and latency. We present a two-year study of Internet routing convergence through the experimental instrumentation of key portions of the Internet infrastructure, including both passive data collection and fault-injection machines at major Internet exchange points. Based on data from the injection and measurement of several hundred thousand interdomain routing faults, we describe several unexpected properties of convergence and show that the measured upper bound on Internet interdomain routing convergence delay is an order of magnitude slower than previously thought. Our analysis also shows that the upper theoretic computational bound on the number of router states and control messages exchanged during the process of BGP convergence is factorial with respect to the number of autonomous systems in the Internet. Finally, we demonstrate that much of the observed convergence delay stems from specific router vendor implementation decisions and ambiguity in the BGP specification     

Joint Monitoring and Routing in Wireless Sensor Networks Using Robust Identifying Codes

Wireless Sensor Networks (WSNs) provide an important means of monitoring the physical world, but their limitations present challenges to fundamental network services such as routing. In this work we utilize an abstraction of WSNs based on the theory of identifying codes. This abstraction has been useful in recent literature for a number of important monitoring problems, such as localization and contamination detection. In our case, we use it to provide a joint infrastructure for efficient and robust monitoring and routing in WSNs. Specifically, we make use of efficient and distributed algorithm for generating robust identifying codes, an NP-hard problem, with a logarithmic performance guarantee based on a reduction to the set k-multicover problem. We also show how this same identifying-code infrastructure provides a natural labeling that can be used for near-optimal routing with very small routing tables. We provide experimental results for various topologies that illustrate the superior performance of our approximation algorithms over previous identifying code heuristics.     

A Graph Drawing Based Spatial Mapping Algorithm for Coarse-Grained Reconfigurable Architectures

Recently coarse-grained reconfigurable architectures (CGRAs) have drawn increasing attention due to their efficiency and flexibility. While many CGRAs have demonstrated impressive performance improvements, the effectiveness of CGRA platforms ultimately hinges on the compiler. Existing CGRA compilers do not model the details of the CGRA, and thus they are i) unable to map applications, even though a mapping exists, and ii) using too many processing elements (PEs) to map an application. In this paper, we model several CGRA details, e.g., irregular CGRA topologies, shared resources and routing PEs in our compiler and develop a graph drawing based approach, split-push kernel mapping (SPKM), for mapping applications onto CGRAs. On randomly generated graphs our technique can map on average 4.5times more applications than the previous approach, while generating mappings which have better qualities in terms of utilized CGRA resources. Utilizing fewer resources is directly translated into increased opportunities for novel power and performance optimization techniques. Our technique shows less power consumption in 71 cases and shorter execution cycles in 66 cases out of 100 synthetic applications, with minimum mapping time overhead. We observe similar results on a suite of benchmarks collected from Livermore loops, Mediabench, Multimedia, Wavelet and DSPStone benchmarks. SPKM is not a customized algorithm only for a specific CGRA template, and it is demonstrated by exploring various PE interconnection topologies and shared resource configurations with SPKM.     

Powering Internet with power-law networking

It is generally recognized that the current routing scheme of Internet suffers from serious scalability problems. In this paper, we work with the abstract but ??Internet-like?? network model consisting of an infinite-variance power-law random graph (IVPLRG). We adopt the idea of a routing scheme proposed by Carmi, Cohen and Dolev (C-C-D). The scheme fits very naturally to the spontaneously emerging ??soft hierarchy?? architecture on an IVPLRG. The use of multiple addresses is suggested as a solution to the inflexibility of the pure C-C-D scheme. A mean-field approximation is introduced for efficient computation of relevant quantitative characteristics and applied to various problems of our scheme. We review a few recent Internet routing proposals and discuss their relation to our scheme. We find out that the topology creation of our scheme offers advantages in terms of scalability and routing policy control.     

On the interplay of network structure and routing strategies in scale-free networks

In this paper, we examine how the structural characteristics of network topologies affect the network performance, and we examine the interplay between structural characteristics of network topologies and routing strategies. We consider routing strategies subject to practical constraints (router technology) and economic considerations (link costs) at layer 3. We propose two new routing methods suitable for implementation in large networks and examine various routing strategies (local, global, and hybrid) with tunable parameters and explore how they can enhance the network performance. We find that there exists an optimal range of values for the tunable parameters to achieve high network performance which depends on the structural properties of the network topology. We also show that our proposed routing scheme, which requires minimum local information, achieves high network performance.     

Network design methods for mitigation of intentional attacks in scale-free networks

Network robustness and network reliability are important issues in the design of Internet Service Providers’ topologies. In this paper, we examine the structural characteristics of network topologies that affect robustness and reliability. We examine the interplay between the structural characteristics of network topologies and the resource capacity over-provisioning strategies when the network breakdowns subject to practical constraints (router technology) and economic considerations (link costs). We study the robustness of the Internet connectivity under node intentional harmful attack using two attacks strategies: static degree-based and static load-based. We find that the robustness of network topologies is affected by the variation of their structural characteristics. In our proposed approach, we show that highly-heterogeneous topologies have less robustness compared with lightly-heterogeneous topologies. The observations from the robustness study provide us useful insights for proposing multiple efficient preventive resource capacity over-provisioning strategies for mitigation of intentional attacks. The proposed strategies utilize the structural properties by calculating the excess traffic in case of single global cascading failure for each node and measure its influence on the other nodes as well as locally. The results show that our proposed strategies can significantly enhance the robustness and increase the resilience of network topology. We also show that highly-heterogeneous topologies have high resilience compared with lightly-heterogeneous topologies. By using real data from the Sprint network at the router level, we provide further empirical evidence in support of the proposed approach.     

Survivable lightpath routing: a new approach to the design ofWDM-based networks

Network restoration is often done at the electronic layer by rerouting traffic along a redundant path. With wavelength-division multiplexing (WDM) as the underlying physical layer, it is possible that both the primary and backup paths traverse the same physical links and would fail simultaneously in the event of a link failure. It is, therefore, critical that lightpaths are routed in such a way that a single link failure would not disconnect the network. We call such a routing survivable and develop algorithms for survivable routing of a logical topology. First, we show that the survivable routing problem is NP-complete. We then prove necessary and sufficient conditions for a routing to be survivable and use these conditions to formulate the problem as an integer linear program (ILP). Due to the excessive run-times of the ILP, we develop simple and effective relaxations for the ILP that significantly reduces the time required for finding survivable routings. We use our new formulation to route various logical topologies over a number of different physical topologies and show that this new approach offers a much greater degree of protection than alternative routing schemes such as shortest path routing and a greedy routing algorithm. Finally, we consider the special case of ring logical topologies for which we are able to find a significantly simplified formulation. We establish conditions on the physical topology for routing logical rings in a survivable manner