János Szigeti

P-cycle Protection in multi-domain optical networks

Providing resilient inter-domain connections in multi-domain optical GMPLS networks is a challenge. On the one hand, the integration of different GMPLS domains to run traffic engineering operations requires the development of a framework for inter-domain routing and control of connections, while keeping the internal structure and available resources of the domains undisclosed to the other operators. On the other hand, the definition of mechanisms to take advantage of such automatically switched inter-domain connectivity is still an open issue. This article focuses on the analysis of applicability of one of these mechanisms: P-cycle-based protection. The proposed solution is based on the decomposition of the multi-domain resilience problem into two sub-problems, namely, the higher level inter-domain protection and the lower level intra-domain protection. Building a P-cycle at the higher level is accomplished by certain tasks at the lower level, including straddling link connection, capacity allocation and path selection. In this article, we present several methods to realize inter-domain P-cycle protection at both levels and we evaluate their performance in terms of availability and spent resources. A discussion on a proposal of implementation of signalling based on extensions of existing protocols such as RSVP-TE and the PCE architecture illustrates the practical viability of the approach.

P-cycle based protection schemes for multi-domain networks

In multi-domain networks, the domains are typically run by different operators, which do not want to share all the internal information with competitors. Furthermore, broadcasting all the internal informations would unnecessarily overload the network with state messages. We decompose the multi-domain resilience problem into two sub-problems, namely the higher level inter-domain protection, and the lower level intra-domain protection. Building p-cycles at the higher level is accomplished by certain tasks at the lower level including straddling link connection, capacity allocation, and path selection. We show that p-cycles offer high availability and acceptable resource usage without the knowledge of paths that makes p-cycles very good candidate for protecting inter-domain traffic.

Multi-domain issues of resilience

This paper gives an overview and classification of issues related to resilience in a multi-layer multi-domain network environment. Then the work focuses on the Internet inter-AS context, where the introduction of G/MPLS capabilities for traffic engineering may enhance the way traffic is exchanged today. This paper shows that, in this context, network resilience based on fast re-routing can be achieved, complementing existing inter-domain link protection strategies, by using alternative disjoint multi-domain backup paths through other domains. Furthermore, the paper proposes a specific method to apply MPLS label stacking to make such backup paths scalable to larger clusters of inter-protected domains by means of MPLS transit. This transit can be used as a temporary solution before BGP routes are stable. Finally, the latest standardisation activity on the provision of such multiple path information for BGP is also reviewed.

Multidomain shared protection with limited information via MPP and p-cycles

The Internet consists of a collection of more than 21,000 domains called autonomous systems operated mostly under different authorities (operators-providers) that, although they cooperate over different geographical areas, compete in a country or other area. Recently, the path computation element concept has been proposed to generalized multiprotocol label switching controlled optical borne networks to make routing decisions for interdomain connections taking into account traffic engineering, quality of service, and resilience considerations. Still the question of protection shareability emerges. For dedicated protection it is enough to know the topology of the network to be able to calculate disjoint paths. However, to reduce network resource usage by sharing of protection resources (e.g., end-to-end shared protection) it is also mandatory to know the exact working and protection path pairs for all the demands. This can be checked within a domain where not only the full topology and link-state information is flooded but also the working and protection paths are known for each connection; however; over the domain boundaries for security and scalability reasons no such information is being spread. We propose using two techniques that do not require flooding the information on working and protection paths while still allowing the sharing of resources. These two techniques are the multidomain p-cycles and the multidomain multipath routing with protection. After explaining the principles of these methods we evaluate the trade-off between the resource requirement and availability of these techniques by simulations.

Efficiency of information update strategies for automatically switched multi-domain optical networks

The routing and wavelength assignment algorithm is a complex task in todays dynamically switched networks. As the number of network nodes and links increases, advertising link states requires more control messages, larger databases and more processing capacity while searching for an available path. Information aggregation in multi-domain networks helps us to reduce the number of advertised links. Furthermore, there are numerous information update strategies that also result in less link state control messages. However, these enhancements are done on the account of information inaccuracy, which leads to higher blocking ratio and longer setup delays. In our article we present a physical device abstraction layer for the control plane where interior optical switches having different multiplexing capabilities and exterior autonomous domains are treated in a unified way. Next we show and analyse solutions for how to apply information update strategies on multilayer networks and how to extend these strategies to fit into multi-domain environment.

/spl lambda/-path fragmentation and de-fragmentation through dynamic grooming

In multi-layer networks, where more than one layer is dynamic, i.e., connections are set up using not only the upper, e.g., IP layer but the underlying wavelength layer as well leads often to suboptimal performance. In this paper we discuss the lightpath fragmentation and de-fragmentation problem, where the lightpath system cannot follow the traffic changes fast enough. We show what it depends on, when is it critical and how much does it deteriorate the performance of the network.

Multi-layer traffic engineering through adaptive λ-path fragmentation and de-fragmentation

In Multi-Layer networks, where more than one layer is dynamic, i.e., connections are set up using not only the upper, e.g., IP layer but the underlying wavelength layer as well leads often to suboptimal performance due to long wavelength paths, that do not allow routing the traffic along the shortest path. The role of MLTE (Multi-Layer Traffic Engineering) is to cut these long wavelength paths into parts (fragments) that allow better routing at the upper layer (fragmentation), or to concatenate two or more fragments into longer paths (defragmentation) when the network load is low and therefore less hops are preferred. In this paper we present a new model (GG: Grooming Graph) and an algorithm for this model that supports Fragmentation and De-Fragmentation of wavelength paths making the network always instantly adapt to changing traffic conditions. We introduce the notion of shadow capacities to model “lightpath tailoring”. We implicitly assume that the wavelength paths carry such, e.g., IP traffic that can be interrupted for a few microseconds and that even allows minor packet reordering. To show the superior performance of our approach in various network and traffic conditions we have carried out an intensive simulation study.

Multi-Domain Resilience: Can I Share Protection Resources with my Competitors?

The Internet consists of a collection of more than 21000 domains called Autonomous Systems (AS) operated mostly under different authorities (operators/providers) that although co-operate over different geographical areas, they compete in a country or other area. Today BGP is the de facto standard for exchanging reachability information over the domain boundaries and for inter-domain routing. The GMPLS controlled optical beared networks are expected to have similar architecture, however, more information has to be carried for TE, resilience and QoS purposes. Therefore, extensions of BGP and of PNNI as well as the PCE have been proposed. Still in all cases emerges the question of protection shareability. For dedicated protection it is enough to know the topology of the network to be able to calculate disjoint paths. However, to be able to perform sharing of protection resources (shared protection) it is not enough to know the topology, but it is mandatory to know exact working and protection path pairs for all the demands, since protection paths can share a certain resource only if there is no such a pair of working paths that contain any element from the same Shared Risk Group (SRG). This can be checked within a domain where the full topology and link-state information is flooded, however, over the domain boundaries for security and scalability reasons no such information is being spread. In this paper we propose using two techniques that do not require flooding the information on working and protection paths while they still allow sharing of resources. These two techniques are the Multi-Domain p- Cycles (MD-PC) and the Multi-Domain Multi-Path Routing with Protection (MD-MPP). After explaining the principles of these methods we give illustrative results.

Evaluation and estimation of the availability of p-cycle protected connections

The availability is an important QoS metric of network connections. We can estimate the availability of a connection based on the availability parameters of the network components. There are several resilience schemes that can be applied to enhance the availability of the connections. However, an accurate approximation can be achieved with simple and fast calculation only for the most basic protection schemes. The more complex the applied protection scheme is the more complex calculation is required to get the exact results. Fortunately, heuristic algorithms have been developed which can give a fast approximation on the price of approximation error, and this error is negligible in the most cases of practical usage.In this paper we examine and compare two methods that can be used to evaluate or to estimate the availability of connections protected by p-cycle protection scheme. The first method, that we propose, focuses on the accuracy, and by exploiting the special properties of p-cycles provides accurate results without enumerating all the possible network or protection configuration states. The second method is the well-known Serial-Parallel availability modeling and calculation method, which is known to be fast (O(n) steps in case of n components), however, its results can have approximation error since the model does not take into account the overlapping of connection components, i.e., when a component is member of more different series.Setting the advantages and disadvantages of these methods against each other, first, we show, that even though, theoretically, the complexity of the proposed algorithm is still exponential (O(2l)), the index (l) does not get high, moreover, it can be kept moderate low if the size and extent of the cycles is constrained. Next, we analyze the approximation error of the Serial-Parallel method. We prove that the estimated availability is always less than the exact one, define an upper bound onto the approximation error of the estimated unavailability and show where does this inaccuracy converge by increasing the availability of the network components.

Incremental availability evaluation model for p-cycle protected connections

QoS routes need availability assurance. Regardless of the applied protection scheme, there are several heuristic algorithms that can approximate the availability of connections based on the availability parameters of network components along the connection path. Accurate approximation can be achieved with simple and fast calculation only for the most basic protection schemes, the more complex the protection scheme is the more complex and long running calculation is required to get the result. Though, the inaccuracy of the heuristic algorithms is negligible in the most cases of practical usage. In this paper we present an availability calculation method for p-cycles that exploits the special properties of the p-cycle protection scheme and provides accurate results without enumerating all the possible network or protection configuration states. The method evaluates the availability of the connection along the working path link-by-link incrementally, pre-calculating also those conditional availabilities of the connection-part that may be used in latter calculations. Theoretically, the complexity of the algorithm is still O(2n), however, in fact n does not get high, moreover, it can be kept moderate low if the size of the cycles is constrained.