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Chapter 7Performance optimisation for the support of TCIS pFor DVB/DAVIC cable networks, this field can be used to provide a faster delivery ofTCIS streams by assigning a higher priority to such streams. In this way, a packet thatarrives at the NIU can be classified according to its ToS requirement and placed in aqueue with two or more levels of prioritisation.In this section, a mixed traffic situation with 41.7 kbps (as described in Section 5.3.3)was used in order to provide a performance analysis when prioritisation for QoS isconsidered. For this analysis only the splitting tree algorithm was used because of itssuperior performance over the exponential backoff algorithm. Results presented here arefor the pure reservation access and the piggyback mechanisms.From Figure 7.12a, it can be seen that packet access delays produced by the PRAmechanism when prioritisation is not supported, were almost the same for both traffictypes. The maximum number of stations supported was 40 for VoIP traffic (with meanaccess delays of under 5 0ms) and 42 for Internet traffic (with mean access delays ofunder 500 ms). This is to be expected, since both traffic types were treated equally.However, from Figure 7.12b when prioritisation was supported, on high traffic loads orcongestion periods (above 44 stations or 59% of the cc), it was seen that packet accessdelays for VoIP traffic produced by the PRA and the PG mechanisms remained atMean Access Delay (ms)3002752502252001751501251007550250a) Without Prioritisation - PRA b) With Prioritisation - PRA & PGInternetTrafficVoIPTraffic34 36 38 40 42 44 46 48 50 52 54umber of Active Stations7-15PRAInternetTrafficPGVoIP TrafficPRA34 36 38 40 42 44 46 48 50 52 54 56 58umbe r of Active StationsFigure 7.12 – Mean access delay vs. No. of active stations for VoIP and Internet traffic.Splitting tree algorithm with and without prioritisation.