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LEVELS OF TRAFFIC BEHAVIOUR So, what kind of traffic behaviour are we interested in for ATM, or IP? In Chapter 3 we looked at the flow of calls in a circuit-switched telephony network, and in Chapter 4 we extended this to consider the flow of cells through an ATM buffer. In both cases, the time between ‘arrivals’ (whether calls or cells) was given by a negative exponential distribution: that is to say, arrivals formed a Poisson process. But although the same source model is used, different types of behaviour are being modelled | Introduction to IP and ATM Design Performance With Applications Analysis Software Second Edition. J M Pitts J A Schormans Copyright 2000 John Wiley Sons Ltd ISBNs 0-471-49187-X Hardback 0-470-84166-4 Electronic 6 Traffic Models you ve got a source LEVELS OF TRAFFIC BEHAVIOUR So what kind of traffic behaviour are we interested in for ATM or IP In Chapter 3 we looked at the flow of calls in a circuit-switched telephony network and in Chapter 4 we extended this to consider the flow of cells through an ATM buffer. In both cases the time between arrivals whether calls or cells was given by a negative exponential distribution that is to say arrivals formed a Poisson process. But although the same source model is used different types of behaviour are being modelled. In the first case the behaviour concerns the use made of the telephony service by customers - in terms of how often the service is used and for how long. In the second case the focus is at the level below the call time scale i.e. the characteristic behaviour of the service as a flow of cells or indeed packets. Figure 6.1 distinguishes these two different types of behaviour by considering four different time scales of activity calendar daily weekly and seasonal variations connection set-up and clear events delimit the connection duration which is typically in the range 100 to 1000 seconds burst the behaviour of a transmitting user characterized as a cell or packet flow rate over an interval during which that rate is assumed constant. For telephony the talk-spurt on off characteristics have durations ranging from a fraction of a second to a few seconds. In IP similar time scales apply to packet flows. cell packet the behaviour of cell or packet generation at the lowest level concerned with the time interval between arrivals e.g. multiples of 2.831 gs at 155.52 Mbit s in ATM 82 TRAFFIC MODELS This analysis of traffic behaviour helps in distinguishing the primary objectives of dimensioning and performance .