Abstract

nkara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2010. Thesis (Ph. D.) -- Bilkent University, 2010. Includes bibliographical references leaves 153-165. We study Traffic Engineering (TE) in Multiprotocol Label Switching (MPLS)/Wavelength Division Multiplexing (WDM) networks and propose a multi-layer TE method. MPLS provides powerful TE features for IP networks and is widely deployed in backbone networks. WDM can increase the transmission capacity of optical fibers to tremendous amounts, therefore it has been the dominant multiplexing technology used in the optical layer. The proposed multi-layer TE solution facilitates efficient use of network resources where the TE mechanisms in the MPLS and WDM layers coordinate. We consider a static WDM layer and available traffic expectation information. The TE problem arising in the considered scenario is the Virtual Topology Design (VTD) problem, which involves the decision of WDM lightpaths to be established, calculation of MPLS Label Switched Paths (LSPs) on the resulting virtual topology, and calculation of the routes and wavelengths in the physical topology that correspond to the lightpaths in the virtual topology. We assume a daily traffic pattern changing with the time of day and aim to design a static virtual topology that satisfies as much of the offered traffic as possible, over the whole day. In our proposed solution, the multi-layer VTD problem is solved by decomposing it into two sub-problems, each involving in a single layer. The decomposition approach is used in the thesis due to the huge computational burden of the combined solution for real-life networks. The sub-problem in the MPLS layer is the design of the lightpath topology and calculation of the LSP routes on this virtual topology. This problem is known to be NP-complete and finding its optimum solution is possible only for small networks. We propose a Tabu Search based heuristic method to solve two versions of this problem, resource oriented and performance oriented. Integer Linear Programming (ILP) relaxations are also developed for obtaining upper and lower bounds. We show that the gap between the produced solutions and the lower and upper bounds are around 10% and 7% for the resource and performance oriented problems, respectively. Since the actual traffic can show deviations from the expected values, we also developed an MPLS layer online TE method to compensate the instantaneous fluctuations of the traffic flows. In the proposed method, the LSPs are rerouted dynamically using a specially designed cost function. Our numerical studies show that using the designed cost function results in much lower blockings than using commonly used Widest Shortest Path First and Available Shortest Path First approaches in the literature. The corresponding sub-problem of the multi-layer VTD problem in the WDM layer is the Static Lightpath Establishment (SLE) problem. Along with the capacity and wavelength continuity constraints, we also consider the Bit Error Rate (BER) constraints due to physical layer impairments such as attenuation, polarization mode dispersion and switch crosstalk. This problem is NP-complete even without the BER constraints. We propose a heuristic solution method and develop an exact ILP formulation to evaluate the performance of the proposed method for small problem sizes. Our proposed method produces solutions close to the optimum solutions for the cases in which the ILP formulation could be solved to optimality. Then, these solution methods for the single layer sub-problems are combined in a multi-layer TE scheme to solve the VTD problem in both layers jointly. The proposed TE scheme considers the physical layer limitations and optical impairments. This TE scheme can be applied by keeping each layer’s information hidden from the other layer, but our simulations show that it can produce more effective and efficient solutions when the physical layer topology information is shared with the MPLS layer. We also investigate the effect of non-uniform optical components in terms of impairment characteristics. The numerical results show that more traffic can be routed when all the components in the network have moderate impairment characteristics, compared to the case in which some components have better and some have worse impairment characteristics. Şengezer, Namık Ph.D.

Abstract

GMPLS is a still developing protocol family which is indented to assume the role of a control plane in transport networks. GMPLS is designed to provide traffic engineering in transport networks composed of different network technologies such as wavelength switched optical networks, Ethernet networks, point-to-point microwave links, etc. Integrating the different network technologies while using label switched paths to provide traffic engineering poses a challenge. The purpose of integrating multiple technologies under a single GMPLS control plane is to enable rapid service provisioning and efficient traffic engineering. Traffic engineering in networks provides two primary advantages, network resource utilization optimization and the ability to provide Quality of Service. Utilizing network resources more efficiently translates to lower expenditures for the network provider. Quality of Service can be used to provide the customer with for example guaranteed minimum bandwidth packet services. Specifically this thesis focused on the problems of signaling and establishing Forward Adjacency Label Switched Paths (FA-LSPs), and on a experimental method of connecting different network technologies. A testbed integrating an Ethernet network and a wave length division multiplexing network was used to show that the proposed solutions can work in practice. GMPLS består av en samling protokoll under utveckling, de är tänkta att anta rollen som kontrollplan i transportnätverk. GMPLS är designat för att tillhandahålla trafikplanering i transportnätverk bestående av flera olika nätverksteknologier såsom Ethernet, våglängds switchande nätverk m.fl. Integration av dessa olika nätverksteknologier under ett gemensamt kontrollplan och uppsättning av ”label switched paths” i dataplanet är en utmaning. Syftet med att integrera multipla teknologier under ett ensamt GMPLS kontroll plan är att snabbt kunna tillhandahålla tjänster över nätverket samt möjliggöra advancerad trafikplanering. Trafikplanering i nätverk ger två stora fördelar, optimering av utnyttjandet av nätverksresurser samt ökade möjligheter att erbjuda ”Quality of Service” till kunder. Bättre utnyttjande av nätverksresurser innebär lägre kostnader för nätverksleverantören medans ”Quality of Service” kan ge kunden t.ex. en garanterad bandbredd. Specifikt fokuserar denna avhandling på problemen med att signalera och etablera ”Forwarding Adjaceny Label Switched Paths” samt en experimentell metod som båda sammankopplar olika typer av nätverk. En testbed bestående av ett Ethernet nätverk samt ett optiskt våglängdsswitchande nätverk användes för att visa att lösningarna kan fungera i praktiken.

Abstract

Date of Conference: 1-5 July 2007 Conference Name: 9th International Conference on Transparent Optical Networks, ICTON 2007 This paper comparatively studies single-layer and multi-layer traffic engineering strategies on an IP/MPLS/WDM network. These strategies are evaluated and compared in two different scenarios. In the first scenario, the strategies make use of statistical information on the traffic patterns. In the second scenario, the traffic engineering decisions are based on the instantaneous traffic information only. The performance and benefits of both approaches are discussed based on simulations considering both throughput and network resource usage. © 2007 IEEE.

Abstract

In this paper, a new traffic engineering-capable routing and wavelength assignment scheme is proposed to efficiently handle LSP and lightpath setup requests with different QoS requirements on modern multi-layer (fully optical core and time-division multiplexed edge) transport networks. The objectives of the proposed algorithm are to minimize the rejection probability by maximizing the network load balancing and efficiently handling the grooming of several LSPs on the same lightpath while respecting the constraints of the optical node architecture and considering both traffic engineering and QoS requirements. The proposed solution consists of a two-stage RWA algorithm: each time a new request arrives, an on-line dynamic grooming scheme finds a set of feasible lightpaths which fulfill the QoS and traffic engineering requirements; then, the best feasible lightpath is selected, aiming to keep the network unbalancing and blocking probability as low as possible in the medium and long term, according to a novel global path affinity minimization concept. Extensive simulation experiments have been performed in which our on-line dynamic RWA algorithm demonstrated significant performances. Thanks to its optimal network resource usage and to its reasonable computational space and time complexity, the algorithm can be very attractive for the next-generation optical wavelength-switched networks. © 2008-2010 - IOS Press and the authors. All rights reserved.