Nortel VoIP Gateway, Configuration Manual

Page: 162 / 220

162 Additional feature configuration
P0606298 02
Enough link capacity
The following table sorts the computations so that for each link, the available link capacity is
compared against the additional IP telephony load. For example, on link R4-R5, there is capacity
(568 kbit/s) to allow for the additional 96 kbit/s of IP telephony traffic.
Some network management systems have network planning modules that determine network
flows. These modules provide more detailed and accurate analysis because they can include
correct node, link and routing information. They also help to determine network strength by
conducting link and node failure analysis. By simulating failures, re-loading network and
re-computed routes, the modules indicate where the network can be out of capacity during failures.
Not enough link capacity
If there is not enough link capacity, consider one or more of the following options:
• Use the G.723.1 codec. Compared to the G.729 codec with 20 ms payload, the G.723.1 codecs
use 29% to 33% less bandwidth.
• Upgrade the bandwidth for the links.
Other intranet resource considerations
Bottlenecks caused by non-WAN resources do not occur often. For a more complete evaluation,
consider the impact of incremental IP telephony traffic on routers and LAN resources in the
intranet where the IP telephony traffic moves across LAN segments that are saturated, or routers
whose central processing unit (CPU) utilization is high.
Table 29 Link capacity example
Link Utilization (%)
Available
capacity
kbit/s
Incremental IP telephony load
Enough
capacity? End
Points Capacity
kbit/s
Threshold Used Site pair
Traffic
kbit/s
R1-R2 1536 85 75 154 Santa Clara/Ottawa
Santa Clara/Tokyo
15.5 Yes
R1-R3 1536
R2-R3 1536
R2-R4 1536
R4-R5 1536 85 48 568 Santa Clara/Richardson
Ottawa/Tokyo
Santa Clara/Tokyo
24 Yes