Nortel VoIP Gateway, Configuration Manual, Page: 165 / 220

Further network analysis 165
Norstar VoIP Gateway Configuration Guide
Reduce packet errors
Packet errors in intranets correlate to congestion in the network. Packet errors are high because the
packets are dropped if they arrive faster than the link can transmit. Identify which links are the
most used to upgrade. This removes a source of packet errors on a distinct flow. A reduction in hop
count provides for less occurrences for routers and links to drop packets.
Other causes of packet errors not related to delay are as follows:
• reduced link quality
• overloaded CPU
• saturation
• LAN saturation
• limited size of jitter buffer
If the underlying circuit has transmission problems, high line error rates, outages, or other
problems, the link quality is reduced. Other services such as X.25 or frame relay can affect the
link. Check with your service provider for information.
Find out what the router threshold CPU utilization level is, and check if the router conforms to the
threshold. If a router is overloaded, the router is continuously processing intensive tasks.
Processing intensive tasks prevents the router from forwarding packets. To correct this,
reconfigure or upgrade the router.
A router can be overloaded when there are too many high-capacity and high-traffic links
configured on it. Ensure that routers are configured to vendor guidelines.
Saturation refers to a situation where too many packets are on the intranet. Packets can be dropped
on improperly planned or damaged LAN segments.
Packets that arrive at the destination late are not placed in the jitter buffer and are lost packets. See
“Adjust the jitter buffer size” on page 164 .
Routing issues
Routing problems cause unnecessary delay. Some routes are better than other routes. The
Traceroute program allows the user to detect routing anomalies and to correct these problems.
Possible high-delay differences causes are:
• routing instability
• wrong load splitting
• frequent changes to the intranet
• asymmetrical routing