Nortel VoIP Gateway, Configuration Manual, Page: 153 / 220

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Norstar VoIP Gateway Configuration Guide
Appendix B
Efficient Networking
This section provides information about making your network run more efficiently.
• “Determining the bandwidth requirements” on page 153
• “Network engineering” on page 154
• “Additional feature configuration” on page 160
• “Further network analysis” on page 163
• “Post-installation network measurements” on page 166
Determining the bandwidth requirements
The IP network design process starts with an IP telephony bandwidth forecast. The bandwidth
forecast determines the following:
• LAN requirements: LAN must have enough capacity for the number of calls plus the overhead
• WAN requirements: WAN must have enough capacity for the number of calls plus the
overhead
Determining WAN link resources
For most installations, IP telephony traffic travels over WAN links within the intranet. WAN links
are the highest recurring expenses in the network and they are often the source of capacity
problems in the network. WAN links require time to receive financial approval, provision and
upgrade, especially inter-LATA (Local Access and Transport Area) and international links. For
these reasons, it is important to determine the state of WAN links in the intranet before installing
IP telephony.
Link utilization
This procedure explains how to determine and adjust link utilization:
1
Get a current topology map and link utilization report of the intranet. A visual inspection of the
topology can indicate the WAN links anticipated to deliver IP telephony traffic.
2 Record the current utilization of the links that will be handling IP telephony traffic. For
example, the link utilization can be an average of a week, a day, or one hour. To be consistent
with the considerations, get the peak utilization of the trunk.
3 Determine the available spare capacity. VoIP Gateway intranets are subject to capacity
planning controls that ensure that capacity use remains below a determined utilization level.
For example, a planning control can state that the utilization of a 56 kbit/s link during the peak
hour must not exceed 50%. For a T1 link, the threshold is higher, at 85%. The carrying
capacity of the 56 kbit/s link can be 28 kbit/s, and for the T1, 1.3056 Mbit/s. In some