Nortel ISDN Signaling Link, Description, Installation And Operation

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ITG Engineering Guidelines Page 125 of 378
ITG Trunk 2.0 ISDN Signaling Link (ISL) Description, Installation and Operation
• Overloaded CPU. This is another commonly-monitored statistic
collected by network management systems. If a router is overloaded, it
means that the router is constantly performing processing-intensive
tasks, which impedes the router from forwarding packets. Find out what
the threshold CPU utilization level is, and check if any suspect router
conforms to the threshold. The router may have to be re-configured or
upgraded.
• Saturation. Routers can be overworked when there are too many high
capacity and high traffic links configured on it. Ensure that routers are
dimensioned according to vendor guidelines.
• LAN saturation. Packets may also be dropped on under-engineered or
faulty LAN segments.
• Jitter buffer too small. Packets that arrive at the destination ITG, but too
late to be placed in the jitter buffer are essentially loss packets as well.
Refer to “Adjust jitter buffer size” on page 124.
Routing issues
Unnecessary delay can be introduced by routing irregularities. A routing
implementation may overlook a substantially better route. A high delay
variation can be caused by routing instability, misconfigured routing,
inappropriate load splitting, or frequent changes to the intranet. Severe
asymmetrical routing results in one site perceiving a poorer quality of service
than the other.
The
WUDFHURXWH program can be used to uncover these routing anomalies.
Subsequently, routing implementation and policies can be audited and
corrected.
Network modeling
Network analysis can be difficult or time-consuming if the intranet and the
expected ITG installation is large. To this end, commercial network modeling
tools exist to analyze what-if scenarios of predicting the effect of topology,
routing, bandwidth, etc. changes to the network. They work with an existing
network management system to load current configuration, traffic and
policies into tool. Network modeling tools can assist the technician to
analyze and try out any of the recommendations given in this document to
predict how delay and error characteristics would change.