Measure intranet QoS 147In contrast, the site pair Santa Clara/Ottawa has both QoS levels of meanand mean+standard deviation falling in the excellent region. The customerhas more confidence that during peak traffic period, the "excellent" servicelevel is likely to be upheld (better than 84% chance under the assumption ofNormal distribution).Other measurement considerationsThe PING statistics described above measure the intranet prior to IP Trunk3.01 (and later) installation, which means that the measurement does nottake into consideration the expected load created by the IP Trunk 3.01 (andlater) users.If the intranet capacity is tight and the IP Trunk 3.01 (and later) trafficsignificant, consider making intranet measurements under load. Load canbe applied using traffic generator tools. The amount of load should matchthe IP Trunk 3.01 (and later)-offered traffic estimated in "IP Trunk 3.01 (andlater) traffic engineering" (page 95).Estimate voice qualityThe perceived quality of a telephone call is dependent on many factors,such as codec characteristics, end-to-end delay, packet loss, and theperception of the individual listener.The E-Model Transmission Planning Tool is a model used to produce aquantifiable measure of voice quality based on relevant factors. Refer to twoITU-T recommendations (ITU-T E.107 and E.108) for more informationon the E-Model and its application.A simplified version of the E-Model is applied to IP Trunk 3.01 (and later) toprovide an estimate of the voice quality that the user can expect, based onvarious configuration choices and network performance metrics.The simplified E-Model is as follows:R = 94 – lc – ld – lpwherelc = codec impairment (see Table 29 "Impairment factors of codecs"(page 148))ld = delay impairment (see Table 30 "Impairment factors due to networkdelay" (page 148))lp = packet loss impairment (see Table 31 "Impairment factors due topacket loss" (page 148))Nortel Communication Server 1000IP Trunk FundamentalsNN43001-563 02.01 StandardRelease 5.5 21 December 2007Copyright © 2007, Nortel Networks.
