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Determining the Non-Existence of a Compatible OSPF Metric
Linköping University, Department of Mathematics, Optimization . Linköping University, The Institute of Technology.
Linköping University, Department of Mathematics, Optimization . Linköping University, The Institute of Technology.ORCID iD: 0000-0001-5907-0087
2004 (English)Report (Other academic)
Abstract [en]

Many telecommunication networks use Internet Protocol for deciding the routing of traffic. The specifications OSPF (Open Shortest Path First) and ECM (Equal Cost Multipath) are very common, and state that each router sends the traffic on the shortest path to the destination. If there are several shortest path, the router splits the traffic evenly. In order to have some control over the traffic distribution, the operator can assign weights to the links in the network, and these weights are used by the routers when calculating the shortest paths. It has been shown that by optimizing over the values of the weights, the performance of a network can be much improved. A difficult question is whether or not for a set of desired traffic patterns there exists a compatible metric, i.e. weights making the routers give the specified traffic patterns. There is one known necessary condition for the existence of such a metric, but up to now no sufficient conditions. We investigate this problem, and find more general necessary conditions for the existence of compatible weights for a set of given desired "shortest path"-graphs. A polynomial algorithm that for most cases verifies the non-existence of a compatible metric is presented. The algorithm also indicates which parts of the traffic patterns that are in conflict. A few numer;cal examples are used to illustrate the procedure, and some computational tests are reported.

Place, publisher, year, edition, pages
Linköping: University of Linköping, Department of Mathematics , 2004. , 42 p.
Series
LiTH-MAT-R, ISSN 0348-2960 ; 6
Keyword [en]
Internet protocol, OSPF, compatible metric, optimization
National Category
Mathematics
Identifiers
URN: urn:nbn:se:liu:diva-22362Local ID: 1569OAI: oai:DiVA.org:liu-22362DiVA: diva2:242675
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-11-06
In thesis
1. Optimization in the Design of OSPF Telecommunication Networks
Open this publication in new window or tab >>Optimization in the Design of OSPF Telecommunication Networks
2004 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis address optimization problems related to the design of lP (Internet Protocol) networks. One of the most commonly used IGP's (Interior Gateway Protocols) in telecommunication networks is the OSPF (Open Shortest Path First) protocol with ECM (Equal Cost Multipath) distribution. This link state based protocol uses link weights, which usually are set by an network operator, for providing routers necessary information regarding how traffic should be routed. By shortest path computations, router decide by themselves how to distribute the traffic.

One problem considered in this thesis is the problem of designing networks which are capable of accommodating large parts of the traffic when network components fails. Link failures are the most common failures, and this is the kind of disturbance which is considered. A multiobjective optimization model is presented and we search for pareto-optimal solutions using a two-phased weight based search method. This method tries to minimize the design cost simultaneously as the level of network survivability is maximized. This method uses the fact that is is easy to compute how traffic is distributed when the OSPF metric is known.

In contrary, it is a much more difficult task to determine if there are any OSPF weights that yield a desired flow distribution. This is a topic which also is studied in the thesis. Necessary conditions, which flow patterns must fulfill for being identical to the shortest paths obtained from OSPF weights, are reported. Sufficient conditions for a special type of flow patterns are also presented. The thesis also contains a polynomial method which can be used for detecting impossibilities in a set of flow patterns when this set do not correspond to the shortest paths of any OSPF weights.

Flow patterns are the basis for a new model which is developed for designing lP networks where OSPF and ECM distribution is used . This model uses a set of in-graphs in order to represent weights implicitly. The model also uses a new set of constraints used for modeling ECM distribution. The usefulness of the model is verified by computational experiments.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2004. 10 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1102
National Category
Mathematics
Identifiers
urn:nbn:se:liu:diva-22354 (URN)1560 (Local ID)91-7373-988-X (ISBN)1560 (Archive number)1560 (OAI)
Presentation
2004-06-03, Sal BL 32, Hus B, Linköpings Universitet, Linköping, 10:15 (Swedish)
Opponent
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-11-06

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Broström, PeterHolmberg, Kaj

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