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Research On Grooming And Protection Algorithms For Multicast Traffic In WDM Mesh Networks

Posted on:2008-08-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:L H LiaoFull Text:PDF
GTID:1118360215450409Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
With the explosive increase in Internet traffic and the emergence of high performance optical network devices, such as OXC and OADM, wavelength-division-multiplexing (WDM) technology will become the core of the next generation backbone networks. Constructing the optical layer over the physical networks through the technique of WDM and wavelength routing can provide huge capacity and re-configurable connections for IP layer, whith will become an important transmission method in the future backbone networks. At the same time, optical networks are required to provide services of high-quality and multi-granularity bandwidth to different users. So it is urgent for optical networks to dynamically set up and tear down connectins on demand. The intelligent optical network (ION) with independent control plane is introduced.Technologies of organizing WDM networks have been attracting more and more attention. The mature of optics technical skills and optical equipments drives more and more work to be done on the optical layer, which usually is dealt with on the higher layers. One example is the optical multicast, which realizes one-to-many routing and cross-connection by using light splitters on the optical layer. In WDM networks, the path route for unicast connection is extended to the tree route for multicast connection. Contrasting to the IP multicast, the optical multicast has some special constraints, e.g., wavelength continuity, light-splitter capability, transceiver number, power loss, and so on. In this dissertation, based on the intelligent optical network with its control plane deploying generalized multi-protocol label switching (GMPLS), the problems of traffic grooming and survivability in WDM mesh networks for the multicast traffic are studied.In WDM optical networks, each wavelength can be operated at very high speed, e.g., OC-48, OC-192 and OC-768's corresponding rates are 2.5Gb/s, 10Gb/s and 40Gb/s, respectively, and the bandwidth provided is coarse granularity. However, in operational networks, there is a huge bandwidth gap between the capacity of a wavelength and the required bandwidth of low-rate traffic streams, e.g., OC-1, OC-3 and OC-12 (their corresponding rates are 51.84Mb/s, 155.52Mb/s and 622.08Mbs/s, respectively). To accommodate such kind of low-rate traffic stream with one lightpath will lead to inefficient resource utilization. And it may not possible to establish end-to-end wavelength channels for all the low-rate connections due to the limitation of wavelengths per fiber and transceivers per node. So it is necessary to investigate the traffic grooming problem in WDM networks.Traffic grooming is the procedure of multiplexing and switching low-speed traffic streams onto high-capacity bandwidth trunks in order to improve bandwidth utilization, optimize network throughput, and minimize network cost. Static traffic grooming can be used for the layout design of WDM grooming networks, or be used for the redesign of network virtual topoloty for a long period. In operational networks, multicast connection requests dynamically arrive and leave. Chapter2 researches the dynamic traffic grooming problem for multicast sessions in WDM mesh networks with the constraints of wavelength continuity, limited wavelengths and transceivers in the network. The node architecture of the multicast and grooming capable cross-connection (MGC-OXC) is presented. The grooming object is analyzed and four multicast groming policies are proposed. We propose a light-tree integrated grooming (LTIG) algorithm to realize multicast traffic grooming in dynamic scenario.Grooming low-rate multicast streams in the sparse-splitting WDM mesh network needs to consider several constraints (e.g. lighting splitting, gromging capability, wavelength number, wavelength conversion, tunable transceiver number and so on), which is a combination optimal problem of multicast routing and low-rate stream grooming. In grooming networks, a node with both the optical splitting and cross-connection architecture and the electronic grooming architecture should be abstracted and described correctly. In Chapter3, a novel auxiliary grooming graph (AGG) is proposed. Through the layered grooming graph model, the multicast light-splitting character, grooming capability and current network resource can be provided. A new efficient multicast traffic grooming algorithm (EMGA) based on the auxiliary graph is proposed, which realizes multicast routing and wavelength assignment for low-speed connection requests in WDM network with sparse-splitting capability. Simulation results show that EMGA has lower traffic blocking probability and good network resource utilization. Since each wavelength channel has the transmission rate over several gigabits per second, the failures of fiber links or nodes may lead a lot of services to be blocked. Therefore, the survivability has emerged as one of important issues in the design of WDM optical networks. The strategy of survivability mainly includes protection and restoration. In protection, the backup resources will be pre-assigned to against the future unknown failures. In restoration, no backup resource is pre-assigned. Only after a failure occurs, the backup resources would be assigned dynamically with the redundant resources in current network. The protection has shorter failures recovery time than the restoration. This dissertation investigates the protection design for multicast sessions in WDM mesh networks, and proposes efficient heuristic algorithms.The concept of shared-risk link groups (SRLG) is introduced by IETF to make networks more robust. In actual networks, different fiber links have the relationship of risks if they traverse the same physical resources (e.g. conduit, cable). Chapter4 investigates the multicast protection problem under the SRLG constraints and proposes an algorithm called dynamic segment shared protection for multicast traffic (DSSPM). The DSSPM adjusts link-cost according to the current network resource state and establish a primary light-tree as well as conrresponding SRLG-disjoint backup segments for a dependable multicast connection request. A backup segment can efficiently share the wavelength capacity of its working tree and the common resources of other backup segments based on SRLG-disjoint constraints. Simulations show that DSSPM not only can protect the multicast sessions against a single-SRLG breakdown, but also can make better use of wavelength resources and lower traffic blocking probability in the network.As the size and complexity of mesh optical networks continue to grow, the multiple failures become increasing probable. Some researches begin to investigate the multiple-link failures problem for unicast traffic. Two link-disjoint backup paths or sub-paths can be pre-computed for each connection and provide complete protection when dual-link failures occur in the network. But the backup resources are occupied more than two times of the primary resources, which may not be afforded for many users. Chapter5 focuses on the shared protection and wavelength capacity reservation for multicast traffic under dual-link failure consideration in WDM optical networks. The network's vulnerable situation and unprotected segments due to link failure are analyzed, and an algorithm called shared segment protection with reprovisioning (SSPR) is proposed. The SSPR can lower the number of unprotected multicast connections, and with the efficient allocation of backup resources it greatly improves mulricast traffic restorability.In the survivability design of WDM optical networks, multicast protection is more complicated and resource consuming than unicast protection. How to reserve less backup resource to protect more multicast sessions in the network and lower the traffic blocking probability is becoming an important research issue.One characteristic of multicast tree is that a failure tree-link may have different effects to the traffic flows carried on the tree. By observing the topoloty of a light-tree, the closer a link is to the tree root, the more important the link is; because more terminals would be disrupted from receiving information from the source due to the link failure. It's important to consider more cost-effectively protecting multicast tree according to differential needs, and reserving backup resource for the critical links under the limited network resources. Chaper6 investigates the partial protection problem for multicast sessions in WDM meshed networks. The aims are to lower traffic blocking probability and achieve tradeoff between protection ability and wavelength resource utilization. A new algorithm called critical-link based partial protection for multicast (CPPM) is proposed. The tree links which carry traffic for multiple destination nodes will be the protection candidates and only one destination node will not receive the data when a single link fails in the network. Simulations show that CPPM can provide certain protection ability and lower multicast traffic blocking probability.To verify and evaluate the proposed algorithms in this dissertation, simulation platform and software is developed. Based on the platform, the performances of all proposed algorithms are evaluated. The platform, model structure and some pseudo codes are given in Chapter7. At last the dissertation is concluded and some research expectatios on multicast traffic groomging and protection design are proposed.
Keywords/Search Tags:Optical Network, Wavelength Division Multiplexing (WDM), Multicast, Traffic Grooming, Survivability, Protection
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