Rüdiger Martin

University of Wuerzburg, Würzburg, Bavaria, Germany

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Publications (29)1.05 Total impact

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    ABSTRACT: The IETF currently discusses fast reroute mechanisms for IP networks (IP FRR). IP FRR accelerates the recovery in case of network element failures and avoids micro-loops during re-convergence. Several mechanisms are proposed. Loop-free alternates (LFAs) are simple but cannot cover all single link and node failures. Not-via addresses can protect against these failures but are more complex, in particular, they use tunneling techniques to deviate backup traffic. In the IETF it has been proposed to combine both mechanisms to merge their advantages: simplicity and full failure coverage.This work analyzes LFAs and classifies them according to their abilities. We qualitatively compare LFAs and not-via addresses and develop a concept for their combined application to achieve 100% single failure coverage, while using simple LFAs wherever possible. The applicability of existing LFAs depends on the resilience requirements of the network. We study the backup path length and the link utilization for both IP FRR methods and quantify the decapsulation load and the increase of the routing table size caused by not-via addresses. We conclude that the combined usage of both methods has no advantage compared to the application of not-via addresses only.
    Computer Networks. 01/2010;
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    ABSTRACT: In this work we compare the efficiency of various routing and resilience mechanisms. Their path layout determines the utilization of links in the network under normal operation and in failure scenarios. For the comparison, the performance measure is the maximum utilization rS of all links for a set of protected failures S. A routing mechanism is considered more efficient than another if it leads to a lower maximum link utilization rS. We consider standard and optimized versions of IP routing and rerouting, optimized routing using explicit paths and end-to-end protection switching, as well as standard and optimized versions of MPLS fast reroute. The results show that routing optimization reduces the maximum link utilization significantly both with and without failure protection. The optimization potential for resilient routing is limited by the applied mechanism and depends heavily on the network structure and the set of protected failure scenarios S.
    European Transactions on Telecommunications 01/2010; Volume 21 Issue 2. · 1.05 Impact Factor
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    ABSTRACT: Multi-topology routing is an increasingly popular IP network management concept that allows transport of different traffic types over disjoint network paths. The concept is of particular interest for implementation of IP fast reroute (IP FRR). The authors have previously proposed an IP FRR scheme based on multi-topology routing called Multiple Routing Configurations (MRC). MRC supports guaranteed, instantaneous recovery from any single link or node failure in biconnected networks as well as from many combined failures, provided sufficient bandwidth on the surviving links. Furthermore, in MRC different failures result in routing over different network topologies, which gives a good control of the traffic distribution in the networks after a failure. In this paper we present two contributions. First we define an enhanced IP FRR scheme which we call 'relaxed MRC' (rMRC). Through experiments we demonstrate that rMRC is an improvement over MRC in all important aspects. Resource utilization in the presence of failures is significantly better, both in terms of paths lengths and in terms of load distribution between the links. The requirement to internal state in the routers is reduced as rMRC requires fewer backup topologies to provide the same degree of protection. In addition to this, the preprocessing needed to generate the backup topologies is simplified. The second contribution is an extension of rMRC that can provide fast reroute in the presence of multiple correlated failures. Our evaluations demonstrate only a small penalty in path lengths and in the number of backup topologies required.
    IEEE Transactions on Network and Service Management 01/2009; Volume 6, Issue 1.
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    ABSTRACT: Multi-topology routing is an increasingly popular IP network management concept that allows transport of different traffic types over disjoint network paths. The concept is of particular interest for implementation of IP fast reroute (IP FRR). First, it can support guaranteed, instantaneous recovery from any link or node failure. Second, different failures result in routing over different network topologies, which augments the parameter space for load distribution optimizations. Multiple Routing Configurations (MRC) is the state-of-the-art IP FRR scheme based on multi-topology routing today. In this paper we present a new, enhanced IP FRR scheme which we call 'relaxed MRC' (rMRC). rMRC simplifies the topology construction and increases the routing flexibility in each topology. According to our experimental evaluation, rMRC has several benefits compared to MRC. The number of backup topologies required to provide protection against the same set of failures is reduced, hence reducing state in routers. In addition, the backup paths are shorter, and the link utilization is significantly better.
    IEEE/IFIP Network Operations and Management Symposium; 01/2008
  • Ruediger Martin, Michael Menth, Ulrich Spoerlein
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    ABSTRACT: Link and router failures lead to disconnection in networks, which can possibly be repaired by restoration and protection switching mechanisms within seconds or milliseconds. However, redirected traffic causes congestion unless sufficient backup capacity is provided for failure scenarios. In previous work we showed that the required backup capacity for the protection switching mechanism ¿self-protecting multipath¿ (SPM) can effectively be reduced by optimized load balancing when resilience against single failures is needed. In this work, we look at double-failure resilience, compare the backup capacity demands for different levels of multi-failure survivability both for the optimized SPM and shortest path routing (SPR), and study the impact of unprotected multi-failures in such networks.
    Photonic Networks, 2007 ITG Symposium on; 06/2007
  • 01/2007;
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    ABSTRACT: Multipath structures are the base for many recently developed rerouting and protection switching mechanisms. All of these methods show a similar path layout, rely on traffic distribution, and promise resilience with only little backup capacity. Therefore, it is hard to recognize their commonalities and differences at first sight. This paper provides an overview of these related mechanisms and a comparative analysis regarding their applicability in optical and packet switched technologies, their path layout, their reaction time, their dynamic adaptability, and many other aspects.
    The 6th International Workshop on Design of Reliable Communication Networks (DRCN); 01/2007
  • Rüdiger Martin, Michael Menth, Ulrich Spörlein
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    ABSTRACT: The self-protecting multipath (SPM) is a simple and efficient end-to-end protection switching mechanism. It distributes traffic according to a path failure specific load balancing function over several disjoint paths and redistributes it if one of these paths fails. SPMs with optimal load balancing functions (oSPMs) are unnecessarily complex because traffic aggregates potentially need to be split which is an obstacle for the deployment of SPMs in practice. The contribution of this paper is the proposal of an integer SPM (iSPM), i.e., the load balancing functions take only 0/1 values and effectively become path selection functions. In addition, we propose a greedy heuristic to optimize the 0/1 distributions. Finally, we show that the iSPM is only little less efficient than the oSPM and that the computation time of the heuristic for the iSPM is clearly faster than the linear program solver for the oSPM such that the iSPM can be deployed in significantly larger networks.
    6th IFIP-TC6 Networking Conference (Networking); 01/2007
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    ABSTRACT: The IETF currently discusses fast reroute mecha- nisms for IP networks (IP FRR) to accelerate the recovery in case of network element failures and to avoid microloops during network-wide routing re-convergence. Several mechanisms are proposed. Loop-free alternates (LFAs) are simple, but they cannot cover all single link and node failures. Not-via addresses are more complex and cover all single failures, but they potentially lead to longer backup paths and require tunnelling which may reduce the forwarding speed of the routers. In addition, they increase the size of the forwarding tables. This work studies the combination of those simple and complex mechanisms to achieve full single failure coverage with least overhead. First, we establish a taxonomy for LFAs according to their ability and propose combination options with not-vias for different resilience requirements. Then, we quantify the effect of combining both mechanisms regarding their applicability for the resilience requirements, routing table size, link util ization, backup path length, and amount of traffic requiring decapsu- lation per router. The results show that there are no strong advantages of the combined application of both mechanisms over not-via as the only IP FRR concept if 100% coverage for single link and node failures is required.
    01/2007;
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    Michael Menth, Rüdiger Martin, Ulrich Spoerlein
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    ABSTRACT: The self-protection multipath (SPM) is a simple protection switching mechanism. It distributes the traffic over several disjoint paths from source to destination according to a traffic distribution function. When a path fails, the traffic is redistributed to the working paths according to another traffic distribution function, i.e., the traffic distribution function depends on the failed path. The contribution of this work is the introduction of a failure-specific traffic distribution function for the SPM that depends on the exact failure of the paths. We present a linear program for the global optimization of the traffic distribution function of all SPMs in all protected failure scenarios. Finally, we compare the amount of protected traffic that can be transported in the network for the conventional SPM and the new failure-specific SPM (FSPM).
    The 6th International Workshop on Design of Reliable Communication Networks (DRCN); 01/2007
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    Michael Menth, Rüdiger Martin, Ulrich Spörlein
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    ABSTRACT: The self-protecting multipath (SPM) is a simple protection switching mechanism that can be implemented, e.g., by MPLS. We present a linear program for the optimization of the SPM load balancing parameters to maximize the amount of transportable traffic with resilience requirements. This is needed to configure the SPM for the deployment in legacy networks. Our study shows that the SPM is very efficient in the sense that it can carry 50% - 200% more protected traffic than IP rerouting in sufficiently meshed networks. The investigation of the computation time and the memory consumption recommends the COIN LP (CLP) as preferred LP solver. The computation time of the program depends mainly on the number of links in the network and networks with up to 240 links can be optimized within one hour on a standard PC.
    Proceedings of IEEE International Conference on Communications, ICC 2007, Glasgow, Scotland, 24-28 June 2007; 01/2007
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    ABSTRACT: Flow-based load balancing algorithms for multipath Internet routing are often used for traffic engineering. However, the target load distribution and the load balanced result agree only on average, and there is a significant inaccuracy over time due to stochastic effects. Dynamic load balancing reduces this inaccuracy by relocating flows to other paths in regular time intervals. This causes packet reordering. Therefore, the flow reassignment rate should be kept low. In this paper we consider load balancing in networks. It differs from load balancing at a single node by the fact that several load balancing steps may be performed at consecutive nodes in series. This affects the flow reassignment rate and the load balancing accuracy due to interdependencies and polarization effects. We quantify the impact by simulation results, explain the observed phenomena, and give recommendations for load balancing in practice.
    IEEE International Conference on Communications (ICC); 01/2007
  • Ruediger Martin, Michael Menth
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    ABSTRACT: MPLS fast reroute (MPLS-FRR) mechanisms deviate the traffic in case of network failures at the router closest to the outage location to achieve an extremely fast reaction time. We review and compare the one-to-one backup and the facility backup concept that are options for MPLS-FRR to deviate the traffic via a detour or a bypass, respectively. Basically, the backup paths can take the shortest path that avoids the outage location from the point of local repair to the tail-end router or to the merge point. We then evaluate the backup capacity requirements and the configuration overhead in terms of the number of backup paths per primary path in a parametric study depending on the network characteristics. While the facility backup concept imposes clearly less configuration overhead than the one-to-one backup, its standard path layout requires more capacity. This can be reduced by a simple modification.
    Photonic Networks, 2006 ITG Symposium on; 05/2006
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    ABSTRACT: This paper studies load balancing for multipath Internet routing. We focus on hash-based load balancing algorithms that work on the flow level to avoid packet reordering which is detrimental for the throughput of transport layer protocols like TCP. We propose a classification of hash-based load balancing algorithms, review existing ones and suggest new ones. Dynamic algorithms can actively react to load imbalances which causes route changes for some flows and thereby again packet reordering. Therefore, we investigate the load balancing accuracy and flow reassignment rate of load balancing algorithms. Our exhaustive simulation experiments show that these performance measures depend significantly on the traffic properties and on the algorithms themselves. As a consequence, our results should be taken into account for the application of load balancing in practice.
    IEEE International Conference on Broadband Communication, Networks, and Systems (BROADNETS); 01/2006
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    Michael Menth, Rüdiger Martin, Joachim Charzinski
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    ABSTRACT: This work focuses on capacity overprovisioning (CO) as an alternative to admission control (AC) to implement qual-ity of service (QoS) in packet-switched communication net-works. CO prevents potential overload while AC protects the QoS of the traffic during overload situations. Overload may be caused, e.g., by fluctuations of the traffic rate on a link due to its normal stochastic behavior (a), by traf-fic shifts within the network due to popular contents (b), or by redirected traffic due to network failures (c). Capac-ity dimensioning methods for CO need to take into account all potential sources of overload while AC can block excess traffic caused by (a) and (b) if the capacity does not suf-fice. The contributions of this paper are (1) the presenta-tion of a capacity dimensioning method for networks with resilience requirements and changing traffic matrices, (2) the investigation of the impact of the mentioned sources of over-load (a-c) on the required capacity for CO in networks with and without resilience requirements, and (3) a comparison of this required capacity with the one for AC. Our results show that in the presence of strong traffic shifts CO requires more capacity than AC. However, if resilience against net-work failures is required, both CO and AC need additional backup capacity for the redirected traffic. In this case, CO can use the backup capacity to absorb other types of over-load. As a consequence, CO and AC have similar bandwidth requirements. These findings are robust against the network size.
    ACM SIGCOMM Computer Communication Review (CCR). 01/2006; 36(4).
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    ABSTRACT: Restoration or protection switching mechanisms protect traffic in packet-switched networks against local outages by deviating it around the failure location. This assures connectivity, but sufficient backup capacity is also needed to maintain quality of service (QoS) for the duration of the outage. To that end, sufficient capacity must be provided on the links so that the network can survive a set of protected failure scenarios without congestion due to redirected traffic. The self- protecting multipath (SPM) is a protection switching mechanism for which the required backup capacity can be minimized by linear optimization methods. However, unprotected multi-failures may lead to congestion in such "resilient networks" since backup capacity may be missing. In this paper, we quantify and compare the impact of unprotected double failures on the QoS for the optimized SPM, single shortest path routing (SSP), and equal- cost multipath (ECMP) routing.
    IEEE Globecom; 01/2006
  • Michael Menth, Rüdiger Martin, Ulrich Spörlein
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    ABSTRACT: The self-protecting multipath (SPM) is a simple protection switching mechanism that can be implemented, e.g., by MPLS. We present a linear program to optimize the SPM load balancing parameters for network dimensioning. Our study shows that the SPM is a very efficient mechanism in the sense that it requires only little backup capacity since it outperforms the p-cycle approach and the shortest path rerouting by far. The investigation of the computation time and the memory consumption recommends the Simplex method as an LP solver rather than an interior point method (IPM). The computation time of the program depends mainly on the number of links in the network and it is well feasible for small and and medium size networks. For large networks, however, fast heuristics are required.
    IEEE International Conference on Communications (ICC); 01/2006
  • Michael Menth, Rüdiger Martin
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    ABSTRACT: The Differentiated Services architecture implements appropriate Per Hop Behaviors (PHBs) for service differentiation to achieve Quality of Service (QoS) in Next Generation Networks (NGNs). In this paper, we review several buffer management and scheduling algorithms that may be applied in this context. The major part of this work focuses on the interaction between TCP and the Modified Earliest Deadline First (MEDF) scheduling algorithm. It is an appealing option for service differentiation because it relies on a single parameter only and because this parameter can be configured independently of the current share of high priority traffic in the network. This is contrary to many other scheduling disciplines or buffer management strategies. The unavailability of this information in today's Internet makes MEDF an interesting candidate for commercial application.
    Computer Communications Journal. 01/2006; Volume 29, Issue 7.
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    ABSTRACT: Restoration and protection switching mechanisms in IP networks are triggered by link or node failures to redirect traffic over backup paths. These mechanisms are no longer effective if a network becomes disconnected after a failure. The risk of end-to-end disconnection increases if the nodes of a network are only sparsely meshed or if multiple network failures occur simultaneously. This leads inevitably to violations of service level agreements with customers and peering network providers. In this paper, we present a method to assess the risk of end-to-end disconnection in IP networks due to network failures. We calculate the disconnection probabilities for all pairs of network nodes taking into account a set of probable network failures. The results are considered from different perspectives. This helps to identify weak spots of the network and to appropriately upgrade its topological infrastructure with additional links. We implemented the concept in a software tool which assists network providers with assessing the risk of disconnection in their network prior to any network failure and to take appropriate actions.
    6th IEEE International Workshop on IP Operations and Management (IPOM); 01/2006
  • Rüdiger Martin, Michael Menth, Korhan Canbolat
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    ABSTRACT: MPLS fast reroute (MPLS-FRR) mechanisms deviate the traffic in case of network failures at the router closest to the outage location to achieve an extremely fast reaction time. We review the one-to-one backup and the facility backup that are options for MPLS-FRR to deviate the traffic via a detour or a bypass around the failed elements, respectively. Basically, the backup paths can take the shortest path that avoids the outage location from the point of local repair to the tail-end router or to the merge point with the primary path. We suggest two simple modifications that lead to a new path layout which can be implemented by one-to-one and by facility backup. We evaluate the backup capacity requirements, the length of the backup paths, and the number of backup paths per primary path in a parametric study regarding the network characteristics. Our proposals save a considerable amount of backup capacity compared to the standard mechanisms. They are suitable for application in practice since they are simple and conform to the standards.
    3rd International Conference on Broadband Communications, Networks, and Systems (BROADNETS 2006), 1-5 October 2006, San José, California, USA; 01/2006