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Chapter 7Performance optimisation for the support of TCIS pFrom Table 7.2 (second and fourth column) we can see that without header suppression(HS) only 55% (for a frame size of 10ms) and 78% (for a frame size of 30ms) is voicedata. According to [47], there is interest in the cable modem communities in removingthe requirement for LLC encapsulation of voice streams at the MAC layer, which wouldincrease the fraction of each voice data in each packet to 63% and 83%, respectively.Further, header suppression involving the RTP, UDP and IP headers would result ineven more significant bandwidth savings. In the simulations it was assumed that theRTP, UDP and IP headers can all be suppressed, which is reasonable if the INAmaintains additional state information on all active voice connections [47]. Thus, theefficiency calculated from Table 7.2 (third and fifth column) is considerably improvedto 91% and 97% for frame sizes of 10 and 30 ms, respectively.Similarly for G.723.1, four configurations were also analysed as indicated in the lastfour columns of Table 7.2. The frame sizes for this codec were of 30 and 120 ms.Table 7.2 – VoIP codecs: G.711 and G.723.1G.711 - 64 kbps (ISD) G.723.1 - 5.3 kbps (Internet)without HS with HS Without with HS without HS with HS without HS with HSFrame Size [ms] 10 10 HS 30 30 30 30 120 120Voice Frame [bytes] 80 80 240 240 20 20 80 80RTP [bytes] 12 0 12 0 12 0 12 0UDP [bytes] 8 0 8 0 8 0 8 0IP [bytes] 20 0 20 0 20 0 20 0LLC [bytes] 3 3 3 3 3 3 3 3SNAP [Bytes] 5 5 5 5 5 5 5 5Ethernet MAC [bytes] 18 0 18 0 18 0 18 0Voice Packet size [bytes] 146 88 306 248 86 28 146 88Net Data rate [kbps] 116.8 70.4 81.6 66.1 22.9 7.5 9.7 5.97-21