Davide Cherubini - PhD Thesis - UniCA Eprints

Chapter 5Traffic MonitoringThis chapter introduces the concept of Traffic Matrix.Moreover, the methodsused to obtain it from data collected by a proprietary tool will be widely described.5.1 Traffic MatrixBasically, a traffic matrix describes the amount of data traffic transmitted betweenevery pair of ingress and egress points in a network. It is a (N −1)×(N −1)matrix, with N = number of nodes, with zeros in its main diagonal. The genericterm a ij indicates the flow originated by node i directed to node j.Obtaining the traffic matrix is not an easy task. Generally an empiric approximationof the matrix is generated, based on network operator’s sensibility.During the meeting with the employers of an important Italian ISP (Tiscali [20]),a criterion has been identified in order to generate the traffic matrix directlyfrom the aggregated flows traversing the links of the Tiscali’s Italian backbonenetwork.In fact, it is easy to observe and collect data from the interfaces of a router regardingthe total amount of traffic flowing on it, with no regard about the sourceof the destination of the flow. Moreover, using this kind of measure, the load ofthe router’s CPU is basically insignificant.The network operators have anticipated that the traffic is usually subdivided asfollows:27