Nortel Networks NN43001-563 - Manual (Page 122)

122 ITG engineering guidelines
where 14 CCS is the larger of two fax traffic parcels (14 CCS as compared
to 6 CCS).
After adjusting for peaking, the incremental data rate on WAN for this route
is 33.2 kbit/s. Compare this number with 24.3 kbit/s when all 60 CCS is
voice 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 bandwidth
requirement of a fax as compared to a voice call (33.7 kbit/s as compared to
11.2 kbit/s) in this example.
This section deals with nodal traffic calculation in both the TLAN subnet and
WAN. It indicates the incremental bandwidth requirement to handle voice
on data networks.
Assess WAN link resources
For most installations, IP Trunk 3.01 (and later) traffic will probably be
routed over WAN links within the intranet. WAN links are the highest
repeating expenses in the network and they often cause capacity problems
in the network. Unlike LAN bandwidth, which is virtually free and easily
implemented, WAN links, especially inter-LATA and international links, take
time to finance, provision, and upgrade. For these reasons, it is important
to determine the state of WAN links in the intranet before installing the IP
Trunk 3.01 (and later) network.
Each voice conversation, (G.729AB codec, 30 ms payload) consumes 11.2
kbit/s of bandwidth or 18.6 kbit/s with Silence Suppression disabled for each
link that it traverses in the intranet. A DS0 64 kbit/s WAN link would support 5
simultaneous telephone conversations with Silence Suppression enabled, or
2 simultaneous telephone conversations with Silence Suppression disabled.
Link utilization
To start this assessment, obtain a current topology map and link utilization
report of the intranet. A visual inspection of the topology map should reveal
which 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 140) .
Next, determine the current utilization of those links. Note the reporting
window that appears in the link utilization report. For example, the link
utilization can be averaged over a week, a day, or one hour. To be consistent
with 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 exhibit
asymmetric traffic behavior, obtain the utilization of the link representing
traffic flowing in the heavier direction.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
.