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Chapter 8Final conclusions pperformance for the support of VoIP traffic, since lower access delays are obtained witha short buffer capacity than with a large buffer size. However, a drawback is that thesmaller the buffer capacity the higher the number of discarded packets, which mayresult in a degradation of service quality. For this analysis the number of discardedpacked resulted in ≈ 3 packets per second when a buffer capacity of 50 ATM cells wasconsidered. This number was of ≈ 1 and 0 for buffer capacities of 1000 and 3000 ATMcells, respectively.In general, from this analysis of buffer capacity, it was found that there is a naturaltrade-off between giving sessions free access to the network and keeping delay at a levellow enough so that interactive applications (e.g. VoIP, audio and video) are supportedand retransmissions or other inefficiencies do not degrade the network performance.From the analysis of the effects of increasing the number of signalling frames it wasfound that by transmitting two signalling frames in the 3 ms period, a slight decrease inaccess delay can be obtained. This reduction resulted in approximately 4 and 5 ms forthe exponential backoff algorithm and the splitting tree algorithm, respectively.However, in terms of system throughput, for the exponential backoff algorithm therewas a decrease in throughput of ≈ 6% of the cc. This reduction was because the numberof contention slots allocated in each signalling frame remained the same, reducing thebandwidth for data transmissions in every 3 ms cycle, in an attempt to resolve fastercollisions.The last analysis of this chapter addressed the effects of varying the packet size inisochronous streams. Here, it was shown that the major factors affecting the systemperformance were seen to be the length of the packet being transmitted for delivery. Inthe analysis of a single node scenario, it was demonstrated that regardless of the offeredload, a station cannot achieve throughput higher than 32% of the maximum channelcapacity in a 3.088 Mbps upstream channel. Even worse, this figure can be as low as1.8% of the cc when delivering minimum Ethernet packets, which is attributed to thescheduler-look ahead delay.8-6