Nortel Networks NN43001-563 - Manual (Page 133)

Implement QoS in IP networks 133
• limiting the maximum frame size and fragmenting large frames on
low-speed WAN links
• limiting the quantity of voice traffic that is transmitted over low-speed
WAN links
Fine-tune network QoS
Topics presented in this section deal with issues that impact the QoS of
IP Trunk 3.01 traffic. They help to understand how to fine-tune a network
to improve its QoS, but are not directly involved as a part of network
engineering procedure. These are advanced topics to help a technician
fine-tune the network to improve QoS, but they are not a part of the required
procedure for initial IP Trunk 3.01 (and later) network engineering.
Further network analysis
This section describes actions that can be taken to investigate the sources
of delay and error in the intranet. This and the next section discuss several
strategies for reducing one-way delay and packet loss. The key strategies
are: as follows:
• reduce link delay
• reduce hop count
• adjust jitter buffer size
• implement IP QoS mechanisms
Components of delay
End-to-end delay is caused by many components. The major components
of delay are as follows:
• propagation delay
• serialization delay
• queuing delay
• routing and hop count
• IP Trunk 3.01 (and later) system delay
Propagation delay
Propagation delay is affected by the mileage and medium of links traversed.
Within an average-size country, the one-way propagation delay over
terrestrial lines is under 18 ms; within the U.S. the propagation delay
from coast-to-coast is under 40 ms. To estimate the propagation delay of
long-haul and trans-oceanic circuits, use the rule-of-thumb of 1 ms per
100 terrestrial miles.
If a circuit goes through a satellite system, estimate each hop between earth
stations to contribute 260 ms to the propagation delay.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
.