Spare capacity provisioning for quasi-static traffic

Resource provisioning has for long been an important area of research in network design. The traffic grooming problem in optical networks is a design problem of aggregating sub-wavelength traffic demands onto lightpaths and lightpaths onto fiber links such that the required electronic switching capability, hence network cost, can be minimized. Because of the reconfiguration cost in optical grooming networks, a reactive resource provisioning approach may become inefficient, and result in revenue loss. In this paper, we propose an over-provisioning scheme, which pre-allocates the spare capacity of lightpaths to dynamic sub-wavelength traffic demands such that the network can be more agile in responding to traffic increment requests. For the single-link case, we formulate the problem as a non-linear programming problem, and for under reasonable assumptions, we prove the objective function is convex. We provide an exact algorithm to find the optimal solution. The problem with general topologies is then studied. We prove the NP-hardness in this case, and propose heuristics. Numerical results show our heuristics perform well.     

Rerouting schemes for dynamic traffic grooming in optical WDM networks

Traffic grooming in optical WDM mesh networks is a two-layer routing problem to effectively pack low-rate connections onto high-rate lightpaths, which, in turn, are established on wavelength links. The objective of traffic grooming is to improve resource efficiency. However, resource contention between lightpaths and connections may result in inefficient resource usage or even the blocking of some connections. In this work, we employ a rerouting approach to alleviate resource inefficiency and improve the network throughput under a dynamic traffic model. We propose two rerouting schemes, rerouting at lightpath level (RRLP) and rerouting at connection level (RRCON) and a qualitative comparison is made between the two. We also propose two heuristic rerouting algorithms, namely the critical-wavelength-avoiding one-lightpath-limited (CWA-1L) rerouting algorithm and the critical-lightpath-avoiding one-connection-limited (CLA-1C) rerouting algorithm, which are based on the two rerouting schemes. Simulation results show that rerouting reduces the blocking probability of connections significantly.     

Optimizing regenerator cost in traffic grooming

In optical networks, regenerators have to be placed on lightpaths every d consecutive nodes in order to regenerate the signal. In addition, grooming enables the use of the same regenerator by several lightpaths. Up to g (the grooming factor) lightpaths can use the same regenerator. In this work we consider the problem of minimizing the number of regenerators used in traffic grooming in optical networks. Starting from the 4-approximation algorithm of Flammini et al. (2010) [10] for d=1 and a path topology, we provide an approximation algorithm with the same approximation ratio for d=1and the ring and tree topologies. We present also a technique based on matching that leads to the same approximation ratio in tree topology and can be used to obtain approximation algorithms in other topologies. We provide an approximation algorithm for general topology that uses this technique. Finally, all the results are extended to the case of general d.     

Policy-Based Grooming in Optical Networks

This work presents a discussion about policies and architecture to aggregate Internet Protocol/Multiprotocol Label Switching (IP/MPLS) traffics within lightpaths. The scenario is that of IP/MPLS client networks over an optical network. It is well known that aggregating lower traffic flows (e.g., packet-based LSPs—Label Switched Path) within higher traffic flows (e.g., lambda-based LSPs) is considered an effective way to maximize the use of the optical network resources. In this work, the policies are divided into two groups. The first one, which solely considers the class of the flow (High Priority—HP or Low Priority—LP), consists of simple policies meant to aggregate packet-based LSPs within lightpaths. In this group, the policies we have defined intend to reduce the optical network overhead to remove and reroute LP LSPs. The second group presents more sophisticated policies taking into account the possibility of having to deal with further transport faults. In this case, the grooming is better planned and the defined policies tend to reduce the negative impact when a failure is detected in the optical transport network. Our approach has been implemented to validate the policies and the results for each group are showed and discussed.     

Traffic grooming, routing, and wavelength assignment in WDM transport networks with sparse grooming resources

While a single fiber strand in wavelength division multiplexing (WDM) has over a terabit-per-second bandwidth and a wavelength channel has over a gigabit-per-second transmission speed, the network may still be required to support traffic requests at rates that are lower than the full wavelength capacity. To avoid assigning an entire lightpath to a small request, many researchers have looked at adding traffic grooming to the routing and wavelength assignment (RWA) problem. In this work, we consider the RWA problem with traffic grooming (GRWA) for mesh networks under static and dynamic lightpath connection requests. The GRWA problem is NP-Complete since it is a generalization of the RWA problem which is known to be NP-Complete. We propose an integer linear programming (ILP) model that accurately depicts the GRWA problem. Because it is very hard to find a solution for large networks using ILP, we solve the GRWA problem by proposing two novel heuristics. The strength of the proposed heuristics stems from their simplicity, efficiency, and applicability to large-scale networks. Our simulation results demonstrate that deploying traffic grooming resources on the edge of optical networks is more cost effective and results in a similar blocking performance to that obtained when distributing the grooming resources throughout the optical network domain.     

一种新的WDM网状网中的动态子通路保护算法

论文研究了业务量疏导WDM网状网中的生存性问题,提出一种新的基于优先级的自适用子通路保护算法(PASPP)。该算法在为子通路寻找保护通路时,高优先级业务可以通过抢占低优先级的业务保护通路来提高其连通率,而同时对低优先级业务也能提供部分保护。仿真结果表明,该算法有较好的性能。     

Survivable power efficiency oriented integrated grooming in green networks

The wide interests in the power savings of IP over wavelength-division-multiplexing (WDM) optical networks have recently risen in both academic and industrial communities. In an effort to tackle this problem, the hybrid grooming (traffic grooming along with an optical bypass) approach has been presented to reduce the power consumed by the entire network infrastructure, including the transmission ports of routers and optical-electrical-optical (OEO) conversions. However, the related works pay little or no attention to the power consumed to ensure the resiliency of the overall network. Meanwhile, the power consumed by components used for establishing lightpaths is not simultaneously taken into account. One survivable network with the higher power efficiency thereby save more power with hybrid grooming, require the lower power consumption of establishing lightpaths and exhibit the shorter recovery time. For the first time, this paper proposes the evaluating models of both survivable power ratio and protection switching time. We subsequently compare two green and survivable grooming heuristics, known as Single-hop Survivable Grooming with considering Power Efficiency (SSGPE) and Multi-hop Survivable Grooming with considering Power Efficiency (MSGPE). Simulation results demonstrate that, MSGPE obtains the higher power efficiency and resiliency although it has the slightly higher time complexity in comparison to SSGPE. Furthermore, it is effective to exploiting waveband merging in our MSGPE to form integrated grooming for further port savings.     

Multi-granularity and robust grooming in power- and port-cost-efficient IP over WDM networks

Previous studies on the power efficiency or port savings in IP over WDM networks have required explicit knowledge of the traffic between each network node pair and the resource assignment of each fiber link. However, it is difficult to estimate this information accurately in live networks, due to the inherent features of IP traffic, e.g., bursts, unpredictability, and variability. Furthermore, the granularity of the demands on an IP-level connection tends to be diverse, and the number of ports consumed in Optical Cross-Connects (OXCs) tends to grow due to the use of hybrid grooming (i.e., traffic grooming with an optical bypass) for power savings. Therefore, it is critical to achieve both power efficiency and port savings in realistic IP over WDM networks. In this paper, we investigate the problem of multi-granularity and robust grooming for power- and port-cost-efficient IP over WDM networks. First, a key parameter, the Multi-Granularity Power Ratio (MGPR), which is the sum of the different single-granularity power ratios, is proposed. Second, the MMPR (Minimizing Multi-granularity Power Ratio) method is used to compute the Traffic Distribution Vectors. Finally, we present the multi-granularity and robust grooming approach, called the Maximizing Hop First (MXHF) approach, where hybrid grooming is adopted to improve power efficiency and waveband merging is utilized to reduce the port cost. Simulation results demonstrate that the MXHF approach can achieve power efficiency and port savings comparing with state-of-the-art robust grooming methods.     

Minimization of SONET ADMs in ring networks revisited

We design improved approximation algorithms for two variants of the ADM minimization problem. SONET add-drop multiplexers (ADMs) are the dominant cost factor in SONET/WDM rings. The number of SONET ADMs required by a set of traffic streams (lightpaths) in a ring is determined by the routing and the wavelength assignment of the traffic streams. We consider both the arc version where the route of each traffic stream is given as input, and the chord version, where the routing is to be decided by the algorithm. The goal in both cases is to assign wavelengths so as to minimize the total number of used SONET ADMs.     

Routing wavelength and time-slot reassignment algorithms for TDM based optical WDM networks

In this paper, we consider the problem of maximizing the time of first lightpath request rejection, T in the circuit-switched time division multiplexed (TDM) wavelength-routed (WR) optical WDM networks. TDM is incorporated into WDM, to increase the channel utilization when the carried traffic does not require the entire channel bandwidth. In TDM–WDM network, multiple sessions are multiplexed on each wavelength by assigning a sub-set of the TDM slots to each session. Thus, given a session request with a specified bandwidth, a lightpath has to be established by using the routing, wavelength and time-slot assignment (RWTA) algorithms. If the lightpath cannot be established, lightpath request rejection or call blocking occurs. As each lightpath is substantial revenue and long-lived, lightpath request rejection is highly unfavourable in the optical backbone networks. In this paper, we are proposing an intelligent routing, wavelength and time-slot reassignment algorithm for multi-rate traffic demands, where, when a call gets blocked, the already established calls in the network are rerouted, wavelength and time-slot reassigned so as to accommodate the blocked call. Since we are talking of slow arrivals and long holding times for the lightpaths, it is possible to do this reassignment while provisioning a new call. Simulation based analyses are used to study the performance of the proposed reassignment algorithm. The results show that the proposed reassignment algorithm can be used to maximize the time of first call blocking, thereby accommodating more calls in the network before upgrading the network capacity.     

A novel admission control mechanism in GMPLS-based IP over optical networks

With the migration of real-time and high-priority traffic in IP networks, dynamic admission control mechanisms are very important in high-capacity networks where IP and optical technologies have converged with a GMPLS-based control-plane. In this paper proposes, we propose an integrated multilayer traffic engineering framework that considers both physical and logical (optical layer) topologies for dynamically admitting new label switched paths (LSPs) in GMPLS networks. The dynamic admission control mechanism is based on an optimal resolution of an integer linear programming model that takes into account both lightpaths availability, wavelength continuity and routing constraints. In order to minimize LSPs set up delays, this mechanism first considers the logical topology (set of lightpaths) that is already in place before setting up a new lightpath for the incoming LSP, resulting in an additional set up signaling delay. When tested by simulations, results confirm that the proposed formulation effectively improves the network performance by reducing the connection blocking rate, while guaranteeing strict delay and noise constraints.     

Dynamic load balancing in IP-over-WDM optical burst switching networks

In this paper, we consider the problem of dynamic load balancing in wavelength division multiplexing (WDM)-based optical burst switching (OBS) networks. We propose a load balancing scheme based on adaptive alternate routing aimed at reducing burst loss. The key idea of adaptive alternate routing is to reduce network congestion by adaptively distributing the load between two pre-determined link-disjoint alternative paths based on the measurement of the impact of traffic load on each of them. We develop two alternative-path selection schemes to select link-disjoint alternative paths to be used by adaptive alternate routing. The path selection schemes differ in the way the cost of a path is defined and in the assumption made about the knowledge of the traffic demands. Through extensive simulation experiments for different traffic scenarios, we show that the proposed dynamic load balancing algorithm outperforms the shortest path routing and static alternate routing algorithms.     

Multilayer Protection with Availability Guarantees in Optical WDM Networks

Survivability is a key concern in modern network design. This paper investigates the problem of survivable dynamic connection provisioning in general telecom backbone networks, that are mesh structured. We assume differentiated services where connections may have different availability requirements, so they may be provisioned differently with protection (if needed) based on their availability requirements and current network state. The problem of effectively provisioning differentiated-service requests, that has been widely investigated for connections routed at the physical layer, assumes peculiar features if we consider sub-wavelength requests at the logical layer that have to be protected (or more generically, whose availability target has to be guaranteed), but also have to be groomed for an efficient use of network resources. An integrated multilayer approach is necessary that considers requirements and grooming of connections at the logical layer as well as their routing and availability at the physical layer. Joint availability-guaranteed routing and traffic grooming may lead to a negative interaction, since the objective of the first problem (guaranteeing a given level of availability to the connections) clashes with the objective of the other problem (minimizing resource consumption). For a multilayer WDM mesh network, we propose new multilayer routing strategies that perform effective availability-guaranteed grooming of sub-wavelength connections. These strategies jointly considers connection availability satisfaction and resource optimization and are developed under two different practical hypotheses: guaranteed target, i.e., a connection is routed only if its availability target is satisfied, and best-effort target, a connection is always routed and, when the availability target cannot be guaranteed, the path with the best possible availability is provisioned. Numerical results are reported and discussed for the two approaches mentioned above. In both cases, the results show high effectiveness of our provisioning strategy.     

Distributed approaches for impairment-aware routing and wavelength assignment algorithms in GMPLS networks

This work proposes two different distributed strategies for provisioning lightpaths in the presence of optical physical-layer impairments in GMPLS networks. The first approach is a more classical one, which introduces new extensions to the OSPF-TE routing protocol. The other approach makes use of an Ant Colony Optimization (ACO) algorithm to adaptively calculate routes in the network by actively monitoring the aggregate optical power of each link.By using an analytical model to incorporate the constraints of the Amplified Spontaneous Emission (ASE) noise of the optical amplifiers into the routing, we demonstrate the effectiveness of our approaches by means of an illustrative numerical example.     

Routing and dynamic resource assignment joint game: a non-cooperative model for QoS routing

In this paper we present an innovative game theoretic non-cooperative model for the quality of service (QoS) routing in communication networks implementing a differentiated service model for the QoS support. The proposed model allows us to solve a joint problem of non-cooperative QoS routing and dynamic capacity allocation over a network of parallel links. This problem is solved by playing a Nash game taking place among players belonging to two categories: (i) the category of individual users, whose objectives are to ship their macroflows from the source node to the destination node, by suitably splitting them over the parallel links, and (ii) the category of capacity players, whose task is to partition and to assign to the classes of traffic upon which the macroflows are mapped, the dynamic portion of capacity over each link. One of the main innovative aspects of our model is that the allocation of the dynamic portion of capacity to each class of traffic over each link is realised during the actual operation of the network, i.e. in conjunction with the QoS routing. Extensive simulation results validate the proposed model, show some of its interesting properties and highlight the remarkable performance enhancements that it achieves with respect to the other results present in the literature.     

一种综合IP层和WDM层资源的光网络动态路由优化模型及其性能研究

在分层图模型的基础上,本文提出一种以最小化全网光路总代价为优化目标的IP over WDM光网络动态路由优化模型,设计了一种针对该模型的在线综合路由算法——MCTLP（Minimizing the Cost of Total Lightpaths）,MCTLP通过综合考虑IP逻辑层带宽资源分配和WDM光物理层波长链路资源的占用以优化网络资源。与两种有代表性的IP over WDM光网络路由算法的性能仿真时比表明：MCTLP能够在IP逻辑层和WDM光物理层都使用较少的链路以承载IP业务流,接纳更多的IP业务连接请求,有效地降低网络阻塞率．     

An improved multiobjective approach inspired by the flashing behaviour of fireflies for Traffic Grooming in optical WDM networks

Nowadays, the traffic demands in optical networks are low-speed traffic requests (low bandwidth requirement of a few Mbps) that employ the huge capacity of a fiber channel (Gbps), causing a waste of bandwidth as a result. Fortunately, by using electronic grooming nodes, we can multiplex (groom) several low-speed demands onto one channel in order to optimize the available resources in an optical network. The problem of grooming low-speed traffic requests is known in the literature as the Traffic Grooming problem and is considered an NP-hard optimization problem. In this work, we use both multiobjective optimization and evolutionary computation with the aim of facing this optical networking problem. The selected evolutionary algorithm is based in the behaviour of fireflies, the Firefly Algorithm (FA). In order to optimize more than one conflicting objective function of the Traffic Grooming problem simultaneously, we have modified the standard FA to the multiobjective domain (MO-FA). After carrying out different experiments with diverse real-world optical networks, comparing the results of the MO-FA with other multiobjective approaches and different standard heuristics for this problem, we can conclude saying that the new version of the MO-FA is an effective approach for dealing with this telecommunication problem.     

Multiple link failures survivability of optical networks with traffic grooming capability

This paper investigates the problem of survivable traffic grooming (STG) in shared mesh optical networks and proposes different frameworks for improving the survivability of low speed demands against multiple near simultaneous failures. Spare capacity reprovisioning has recently been considered for improving the overall network restorability in the event of dual failures; here, after the recovery form the first failure, some connections in the network may become unprotected and exposed to new failures. Capacity reprovisioning then allocates protection resources to unprotected and vulnerable connections so that the network can withstand a future failure. In this paper, we propose two different reprovisioning schemes (lightpath level reprovisioning, LLR, and connection level reprovisioning, CLR); they differ in the granularity at which protection resources are reprovisioned. Further, each of these schemes is suitable for a different survivable grooming policy. While LLR provides collective reprovisioning of connections at the lightpath level, CLR reprovisions spare bandwidth for lower speed connections instead. We use simulation methods to study the performance of these schemes under two grooming policies (PAL and PAC), and we show that while CLR reprovisions substantially many more connections than LLR (i.e., potentially more management overhead) CLR yields a much better network robustness to simultaneous failures due to its superior flexibility in using network resources.     

Applying MOEAs to solve the static Routing and Wavelength Assignment problem in optical WDM networks

Wavelength-Division Multiplexing (WDM) in optical networks has revolutionized the Telecommunication field. This technology is able to exploit the enormous bandwidth capability of this kind of networks, allowing communication between end users via all-optical WDM channels (lightpath). Given a set of demands, the problem of setting up lightpaths by routing and assigning a wavelength to each connection is known as Routing and Wavelength Assignment (RWA) problem. There are two types of connection demands: static (demands are given in advance) and dynamic (demands are given in real-time). In this paper we present two different Multiobjective Evolutionary Algorithms (MOEA) with the aim of solving the static RWA problem. The first one is a population-based algorithm, the Differential Evolution (DE), but incorporating the Pareto Tournament concept (DEPT). The second one is a multiobjective version of the Variable Neighborhood Search (VNS), MO-VNS. In order to prove the goodness of our metaheuristics, we have compared them with the standard Fast Non-Dominated Sorting Genetic Algorithm (NSGA-II), typical heuristics in the Telecommunication field, and different varieties of Multiobjective Ant Colony Optimization Algorithms. On the whole, we conclude that our approaches have obtained very promising results.     

光纤Mesh网络动态组播业务疏导算法

针对当前低速组播业务请求与光网络高速波长传输容量的问题,基于光网络组播业务疏导模型,提出动态组播业务疏导算法,将新的组播业务请求疏导到已建立的光组播树上,达到提高网络资源的利用率、降低组播业务连接阻塞概率的目的。仿真结果表明,该算法可有效地改善网络性能。