Nortel Networks NN43001-563 - Manual (Page 165)

Post-installation network measurements 165
When a system equipped with an IP Trunk 3.01 (and later) node serves as a
tandem switch in a network where some circuit-switched trunk facilities have
an excessively low audio level, Silence Suppression, if enabled, degrades
the quality of service by causing choppiness of speech.
Under tandem switching conditions where loss level cannot compensate,
disable Silence Suppression using the TM 3.1 ITG ISDN Trunk Node
Properties DSP profile tab codec options sub-tab. See Step 8 on
Step 8 .
Disabling Silence Suppression approximately doubles LAN/WAN bandwidth
use. Disabling Silence Suppression consumes more real-time on the IP
trunk card.
Table 17 "Silence Suppression disabled TLAN Ethernet and WAN IP
bandwidth usage per IP Trunk 3.01 (and later) " (page 113)
shows the
bandwidth requirement when Silence Suppression is disabled. This does
not impact the data rate for fax, since fax does not have Silence Suppression
enabled.
Fallback threshold
There are two parameters, the receive fallback threshold and the transmit
fallback threshold, which can be configured on a per-site pair basis.
"Set QoS expectations" (page 140) and "Measure intranet QoS" (page 140)
sections describe the process of determining the appropriate QoS level
for operating the IP Trunk 3.01 (and later) network. Site pairs can have
very different QoS measurements if some traffic flows are local, while other
traffic flows are inter-continental. Consider setting a higher QoS level for
the local sites compared to the international sites, thus keeping costs of
international WAN links down.
Normally, the fallback threshold in both directions is set to the same QoS
level. In site pairs where one direction of flow is more important, set up
asymmetric QoS levels.
Setting the QoS threshold for fallback routing
The QoS thresholds for fallback routing are configured in TM 3.1. A
threshold is configured for the "Receive fallback threshold" as well as the
"Transmit fallback threshold." The available thresholds are Excellent, Good,
Fair, and Poor.
Post-installation network measurements
The design process is continual, even after implementation of the IP Trunk
3.01 (and later) network and commissioning of voice services over the
network. Network changes in the following – IP Trunk 3.01 (and later) traffic,
general intranet traffic patterns, network policies, network topology, user
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
.