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Chapter 7Performance optimisation for the support of TCIS p⎛ Pk ⎞size ⎛ RS ⎞S⎜⎟max= CC ⋅ ⋅ ⎜ ⎟(7.1)⎝ Pkslots⎠ ⎝ RS + CS ⎠Smaxmax=(7.2)⋅ λPk sizewhere RS and CS corresponds to the number of slots to be allocated to the reservationand contention access respectively. For instance, for the codec G.723.1 with a framesize of 30 ms (20 bytes of sampling), without header suppression the audio packet sizeto be transmitted becomes of 86 bytes (see Table 7.2, fifth column). Then, fromEquations 7.1 and 7.2,⎛ 86 ⋅ 8 ⎞ ⎛ 8 ⎞Smax= 6176000 ⋅ ⎜ ⎟ ⋅ ⎜ ⎟ = 3688 kbps = 59.7% of the cc⎝ 2 ⋅ 64 ⋅8⎠ ⎝ 8 + 1⎠maxS=maxSmax 3688000= =≈ 161⋅ λ (86 ⋅8)⋅ (1/ 0.03)rP sFrom simulations using this codec, a maximum system throughput of 59% of the cc anda maximum number of streams supported of 160 was obtained. Thus, theoretical resultswere seen to be similar. In general, for all four configurations presented for each codeca maximum deviation between simulation results and theoretical results was found to beless than 1.5%. This deviation can be attributed mainly to collisions and protocoloverheads.7.4 Comparison: DVB/DAVIC vs. DOCSISSo far only a performance characterisation and optimisation for the European cablecommunication system ‘DVB/DAVIC’, under various configurations and differenttraffic situations has been introduced. However, as stated in Section 2.5, theEuroDOCSIS protocol is also a serious alternative for the European market.This section continues with a comparison between both standardised cablecommunication protocols: DVB/DAVIC vs. DOCSIS. The comparison focuses onperformance issues and technical characteristics at the MAC and PHY layers.7-24