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Fulfilling efficiently SLA availability guarantees in backbone networks
Norwegian University of Science and Technology, Faculty of Information Technology, Mathematics and Electrical Engineering, Department of Telematics.
2014 (English)MasteroppgaveStudent thesis
Abstract [en]

The availability and reliability of backbone networks is important to society. However, physical, software and unintentional human error failures affect the links and nodes in a backbone network. To overcome such failures in the network, recovery mechanisms such as Protection and Restoration are utilized. Additionally, a concept of Service Level Agreement (SLA) is introduced between the provider and the user which defines and guarantees the network availability requirements and penalty schemes. In this thesis, fulfilling the SLA availability guarantee efficiently in a backbone network is investigated. This thesis focuses on the problem of handling end-to-end path failures on backbone networks. Some of the popular existing recovery mechanisms to handle such failures are Dedicated Backup Path Protection (DBPP) and Path Restoration (PR). A high percentage of network survivability can be achieved by DBPP with a reserved backup path for each provisioned connection. Unfortunately, it is very costly and resource demanding. Whereas, a PR based solution consumes only the needed resources but it is very slow to recover from failure which might effect the SLA availability guarantee. The work in this thesis aims at providing a hybrid network recovery model that combines the benefits of both DBPP and PR. The hybrid model switches between DBPP and PR according to the SLA availability requirement over a contract period and the current network connection state (i.e. the remaining time of the SLA and current sum of downtimes (accumulated downtime)). Moreover, an analysis in the failure logs of UNINETT’s backbone network is made to model the probability distribution of the accumulated downtime that uses PR. A distribution fitting is made for modeling the connection downtime data taken from UNINETT’s backbone network where Weibull distribution proved to be a good approximation. Additionally, a model for distribution of accumulated downtime that uses DBPP for both non-simultaneous and simultaneous failures of the working path and backup path is provided. An in-depth explanation of how these distributions models can be used in the design of hybrid models is presented. Two hybrid models were approached in this thesis. The first hybrid approach used the DBPP scheme at the beginning of the SLA duration and then it switches to PR when the calculated SLA risk assessment shows that the probability of violating the SLA requirement is lower at time t. The second hybrid approach used the PR scheme at the beginning of the SLA duration and then it switches to DBPP when the accumulated downtime at time t reach near to the threshold of the SLA risk target such that the probability of violating the SLA requirement is higher. The transition line which decides the switching between PR and DBPP are computed for each hybrid approach using the results obtained from the accumulated downtime distribution model of PR and DBPP. The transition line defined in this thesis provides information about when the connection should switch between Protection and Restoration mechanism by knowing the network connection state. The computed transition lines with a 1 percent SLA risk target is verified via discrete event simulation in DEMOS. The SLA risk target is the probability of failing the SLA, however the provider can tune the risk target by using an advanced network recovery mechanism (e.g Protection) for more or less time. The simulation results showed that the proposed hybrid models work well, fulfilling the SLA availability guarantee efficiently with respect to the resource utilization. In addition, the results also revealed that using the PR scheme at the beginning of the SLA contract provides three times better resource utilization than using the DBPP scheme at the beginning. Cost analysis for network providers are made with different SLA risk targets in order to find the optimal SLA risk target for network providers. The results from analysis suggested that the total cost for network providers decreases with the increase of SLA risk target until the total cost reaches its minimum, then it starts to increase again. The result of this thesis might contribute to future research on developing a hybrid model to reach particular performance objectives in communication networks.

Place, publisher, year, edition, pages
Institutt for telematikk , 2014. , 93 p.
Keyword [no]
ntnudaim:10973, MTKOM Kommunikasjonsteknologi, Tele√łkonomi
URN: urn:nbn:no:ntnu:diva-27342Local ID: ntnudaim:10973OAI: diva2:769316
Available from: 2014-12-07 Created: 2014-12-07

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