Nortel Meridian ITG Line 2.0 Description, Installation And Operation Manual page 83

The ITG Line 2.0 card node and the T-LAN router should be placed as close
to the WAN backbone as possible in order to:
• minimize the number of router hops.
• segregate constant bit-rate Vo IP traffic from bursty LAN traffic.
• simplify the end-to-end QOS engineering for packet delay, jitter, and
packet loss.
If an access router separates the ITG Line 2.0 card node from the WAN
router, there must be a high-speed link (for example, Fast Ethernet, FDDI,
SONET, OC-3c, ATM STS-3c) between the access router and the WAN
backbone router.
Reducing packet errors
Packet errors in intranets are generally correlated with congestion somewhere
in the network. Bottleneck links tend to be where the packet errors are high
because packets get dropped when they arrive faster than the link can transmit
them. The task of upgrading highly utilized links should also remove the
source of packet errors on a particular flow. Also an effort to reduce hop count
gives fewer opportunities for routers and links to drop packets.
Other causes of packet errors, not related to queueing delay, are as follows:
• Poor link quality. The underlying circuit may have transmission
problems, high line error rates, subject to frequent outages, etc. Note that
the circuit may be provisioned on top of other services, such as X.25,
frame relay, or ATM. Check with the service provider for resolution.
• 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 also 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.
ITG Line 2.0/i2004 Internet Telephone Description, Installation, and Operation
IP Network engineering guidelines Page 83 of 302