Nortel Networks NN43001-563 - Manual (Page 127)

Implement QoS in IP networks 127
Insufficient link capacity
If there is not enough link capacity, implement one or more of the following
options:
• Use the G.723 codec series.
Compared to the default G.729AB codec with 30 ms payload, the G.723
codecs use 9% to 14% less bandwidth.
• Upgrade the link’s bandwidth.
Other intranet resource considerations
Bottlenecks caused by non-WAN resources are less frequent. For a more
complete assessment, consider the impact of incremental IP Trunk 3.01
(and later) traffic on routers and LAN resources in the intranet. Perhaps
the IP Trunk 3.01 (and later) traffic is traversing LAN segments that are
saturated, or traversing routers whose CPU utilization is high.
Implement QoS in IP networks
Today’s corporate intranets developed because of the need to support
data services, services which found a "best effort" IP delivery mechanism
sufficient. Standard intranets are designed to support a set of QoS
objectives dictated by these data services.
When an intranet takes on a real-time service, such as VoIP, the users of
that service impose additional QoS objectives on the intranet. Some of
these targets are less stringent compared with those imposed by current
services, while other targets are more stringent. If a data intranet not
exposed to real-time services in the past now has to deliver IP Trunk 3.01
(and later) traffic, the QoS objectives for delay impose an additional design
constraint on the intranet.
One approach is to simply subject all intranet traffic to additional QoS
constraints and design the network to the strictest QoS objectives. This
would improve the quality of data services, even though most applications
might not perceive a reduction of, for example, 50ms in delay. Improving the
network results in one that would be adequately engineered for voice, but
over-engineered for data services.
The best approach to consider is the use of QoS mechanisms in the intranet
when the intranet is carrying mixed traffic types.
QoS mechanisms are extremely important to ensure satisfactory voice
quality. If QoS mechanisms are not used, there is no guarantee that the
bandwidth needed for voice traffic will be available. For example, a data file
being downloaded from the intranet could use most of the WAN bandwidth.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
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