2 research outputs found
Multi-layer traffic engineering in optical networks under physical layer impairments
Ankara : 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, NamıkPh.D
A tabu search algorithm for sparse placement of wavelength converting nodes in optical networks
Cataloged from PDF version of article.All-optical Wavelength Division Multiplexing networks, providing extremely
large bandwidths, are among the most promising solutions for the increasing
need for high-speed data transport. In all-optical networks, data is transmitted
solely in the optical domain along lightpaths from source to destination without
being converted into the electronic form, and each lightpath is restricted to use
the same wavelength on all the links along its path. This restriction is known as
the wavelength continuity constraint. Optical wavelength conversion can increase
the performance and capacity of optical networks by removing this restriction
and relaxing the wavelength continuity constraint. However, optical wavelength
conversion is a difficult and expensive technology. In this study, we analyze the
problem of placing limited number of wavelength converting nodes in a multi-
fiber network with static traffic demands. Optimum placement of wavelength
converting nodes is an NP-complete problem. We propose a tabu search based
heuristic algorithm for this problem. The objective of the algorithm is to achieve
the performance of full wavelength conversion in terms of minimizing the total number of fibers used in the network by placing minimum number of wavelength
converting nodes. Numerical results comparing the performance of the algorithm
with the optimum solutions are presented. The proposed algorithm gives quite
satisfactory results, it also has a relatively low computational complexity making
it applicable to large scale networks.Şengezer, NamıkM.S