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Chapter 5Upstream channel capacity and characterisation pplanning as well as identifying the limits of the different levels of service that can beprovided to subscribers.For all the configurations defined above we need to find saturation points and thereasons for inefficiencies, as well as how optimal features such as the use of the splittingtree algorithm to resolve collisions could possibly improve the overall systemperformance.5.3 Traffic type characteristics and system parametersAs stated in Section 4.3.2, each station has been enabled with two traffic sources, thefirst traffic source generates Internet traffic and the second generates either VoIPstreams or isochronous streams. In this chapter we base our analysis on these two trafficsources to examine the impact and trade-offs on system performance of four differenttopical traffic types: Internet traffic, Voice over IP (VoIP), mixed traffic, andisochronous streams, (described below) and at the same time providing a performancecharacterisation of the DVB/DAVIC protocol.5.3.1 Internet trafficThis generator emulates Internet traffic. From available traffic measurement studies [46]and [53], it is known that the frequency of Ethernet packets is as indicated in Table 5.1,which also presents the number of ATM cells required per packet and the total packetsize to be transmitted. It is expected that most upstream packets will beacknowledgements of the higher bandwidth downstream packets. Hence, the majority ofpackets generated will be 64 bytes long and packet sizes of 1518 bytes correspond to themaximum size of Ethernet packets that are mainly used by File Transfer Protocol (FTP)applications.Packet Size(bytes)Table 5.1- Packet size distribution and characterisation.Probability ofoccurrenceumber ofATM cellsTransmitted packetsize with overhead64 0.6 2 128 1128 0.06 3 192 1256 0.04 6 384 1512 0.02 11 704 11024 0.25 22 1408 25-3umber of signallingframes required