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THE QUEUEING BEHAVIOUR OF PACKETS IN AN IP ROUTER BUFFER In Chapters 7 and 8, we investigated the basic queueing behaviour found in ATM output buffers. This queueing arises because multiple streams of cells are being multiplexed together; hence the need for (relatively short) buffers. We developed balance equations for the state of the system at the end of any time slot, from which we derived cell loss and delay results. | 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 PART III IP Performance and Traffic Management 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 14 Basic Packet Queueing the long and short of it THE QUEUEING BEHAVIOUR OF PACKETS IN AN IP ROUTER BUFFER In Chapters 7 and 8 we investigated the basic queueing behaviour found in ATM output buffers. This queueing arises because multiple streams of cells are being multiplexed together hence the need for relatively short buffers. We developed balance equations for the state of the system at the end of any time slot from which we derived cell loss and delay results. We also looked at heavy-traffic approximations explicit equations which could be rearranged to yield expressions for buffer dimensioning and admission control as well as performance evaluation. In essence packet queueing is very similar. An IP router forwards arriving packets from input port to output port the queueing behaviour arises because multiple streams of packets from different input ports are being multiplexed together over the same output port . However a key difference is that packets do not all have the same length. The minimum header size in IPv4 is 20 octets and in IPv6 it is 40 octets the maximum packet size depends on the specific sub-network technology e.g. 1500 octets in Ethernet and 1000 octets is common in X.25 networks . This difference has a direct impact on the service time to take this into account we need a probabilistic rather than deterministic model of service and a different approach to the queueing analysis. As before there are three different types of behaviour in which we are interested the state probabilities by
