17 research outputs found
Learning algorithms for the control of routing in integrated service communication networks
There is a high degree of uncertainty regarding the nature of traffic on future integrated service networks. This uncertainty motivates the use of adaptive resource allocation policies that can take advantage of the statistical fluctuations in the traffic demands. The adaptive control mechanisms must be 'lightweight', in terms of their overheads, and scale to potentially large networks with many traffic flows. Adaptive routing is one form of adaptive resource allocation, and this thesis considers the application of Stochastic Learning Automata (SLA) for distributed, lightweight adaptive routing in future integrated service communication networks. The thesis begins with a broad critical review of the use of Artificial Intelligence (AI) techniques applied to the control of communication networks. Detailed simulation models of integrated service networks are then constructed, and learning automata based routing is compared with traditional techniques on large scale networks. Learning automata are examined for the 'Quality-of-Service' (QoS) routing problem in realistic network topologies, where flows may be routed in the network subject to multiple QoS metrics, such as bandwidth and delay. It is found that learning automata based routing gives considerable blocking probability improvements over shortest path routing, despite only using local connectivity information and a simple probabilistic updating strategy. Furthermore, automata are considered for routing in more complex environments spanning issues such as multi-rate traffic, trunk reservation, routing over multiple domains, routing in high bandwidth-delay product networks and the use of learning automata as a background learning process. Automata are also examined for routing of both 'real-time' and 'non-real-time' traffics in an integrated traffic environment, where the non-real-time traffic has access to the bandwidth 'left over' by the real-time traffic. It is found that adopting learning automata for the routing of the real-time traffic may improve the performance to both real and non-real-time traffics under certain conditions. In addition, it is found that one set of learning automata may route both traffic types satisfactorily. Automata are considered for the routing of multicast connections in receiver-oriented, dynamic environments, where receivers may join and leave the multicast sessions dynamically. Automata are shown to be able to minimise the average delay or the total cost of the resulting trees using the appropriate feedback from the environment. Automata provide a distributed solution to the dynamic multicast problem, requiring purely local connectivity information and a simple updating strategy. Finally, automata are considered for the routing of multicast connections that require QoS guarantees, again in receiver-oriented dynamic environments. It is found that the distributed application of learning automata leads to considerably lower blocking probabilities than a shortest path tree approach, due to a combination of load balancing and minimum cost behaviour
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
Efficient Passive Clustering and Gateways selection MANETs
Passive clustering does not employ control packets to collect topological information in ad hoc networks. In our proposal, we avoid making frequent changes in cluster architecture due to repeated election and re-election of cluster heads and gateways. Our primary objective has been to make Passive Clustering more practical by employing optimal number of gateways and reduce the number of rebroadcast packets
Semantic discovery and reuse of business process patterns
Patterns currently play an important role in modern information systems (IS) development and their use has mainly been restricted to the design and implementation phases of the development lifecycle. Given the increasing significance of business modelling in IS development, patterns have the potential of providing a viable solution for promoting reusability of recurrent generalized models in the very early stages of development. As a statement of research-in-progress this paper focuses on business process patterns and proposes an initial methodological framework for the discovery and reuse of business process patterns within the IS development lifecycle. The framework borrows ideas from the domain engineering literature and proposes the use of semantics to drive both the discovery of patterns as well as their reuse