Assess WAN link resources 121where 14 CCS is the larger of two fax traffic parcels (14 CCS as comparedto 6 CCS).After adjusting for peaking, the incremental data rate on WAN for this routeis 33.2 kbit/s. Compare this number with 24.3 kbit/s when all 60 CCS isvoice traffic, it appears that the reduction in CCS due to one-way fax traffic(20 CCS as compared to 14 CCS) will not compensate for higher bandwidthrequirement of a fax as compared to a voice call (33.7 kbit/s as compared to11.2 kbit/s) in this example.This section deals with nodal traffic calculation in both the TLAN subnet andWAN. It indicates the incremental bandwidth requirement to handle voiceon data networks.Assess WAN link resourcesFor most installations, IP Trunk 3.01 (and later) traffic will probably berouted over WAN links within the intranet. WAN links are the highestrepeating expenses in the network and they often cause capacity problemsin the network. Unlike LAN bandwidth, which is virtually free and easilyimplemented, WAN links, especially inter-LATA and international links, taketime to finance, provision, and upgrade. For these reasons, it is importantto determine the state of WAN links in the intranet before installing the IPTrunk 3.01 (and later) network.Each voice conversation, (G.729AB codec, 30 ms payload) consumes 11.2kbit/s of bandwidth or 18.6 kbit/s with Silence Suppression disabled for eachlink that it traverses in the intranet. A DS0 64 kbit/s WAN link would support 5simultaneous telephone conversations with Silence Suppression enabled, or2 simultaneous telephone conversations with Silence Suppression disabled.Link utilizationTo start this assessment, obtain a current topology map and link utilizationreport of the intranet. A visual inspection of the topology map should revealwhich WAN links are likely to be used to deliver IP Trunk 3.01 (and later)traffic. Alternately, use the Traceroute tool. See "Measure intranet QoS"(page 139).Next, determine the current utilization of those links. Note the reportingwindow that appears in the link utilization report. For example, the linkutilization can be averaged over a week, a day, or one hour. To be consistentwith the dimensioning considerations, obtain the busy period (peak hour)utilization of the trunk. See "IP Trunk 3.01 (and later) traffic engineering"(page 95). Because WAN links are full-duplex and data services exhibitasymmetric traffic behavior, obtain the utilization of the link representingtraffic flowing in the heavier direction.Nortel Communication Server 1000IP Trunk FundamentalsNN43001-563 02.01 StandardRelease 5.5 21 December 2007Copyright © 2007, Nortel Networks.
