Reducing Delays - Nortel Remote Office 9150 Installation And Administration Manual

Network engineering guidelines

Reducing delays

Introduction
This section provides guidelines for reducing one-way delay and packet loss in
the Remote Office network.
Reducing link delay
The time it takes for a voice packet to be queued on the transmission buffer of a
link until it is received at the next hop router is the link delay. Link delay can be
reduced by
upgrading link capacity
This reduces the serialization delay of the packet, but also more
significantly it reduces the utilization of the link and the queueing delay. To
estimate how much delay can be reduced, refer to the tables and formulas
given in "Serialization delay" on page 409 and "Queuing delay" on
page 410. Before upgrading a link, you must check both routers connected
to the link intended for the upgrade and ensure that router configuration
guidelines are complied with.
changing the link from satellite to terrestrial
This should reduce the link delay by 100 to 300 ms.
implementing a priority queueing discipline
See "Queue management" on page 418.
To determine which links should be considered for upgrading, first list all the
intranet links used to support the Remote Office traffic, which can be derived
from the traceroute output for each site pair. Then, using the intranet link
utilization report, note the highest utilized or the slowest links, or both. Estimate
the link delay of suspect links using the traceroute results.
Suppose that a 256 Kbps link from Router 1 to Router 2 has a high utilization.
The following is a traceroute output that traverses this link:
Richardson3 % traceroute santa_clara_Remote Office4
traceroute to santa_clara_Remote Office4 (10.3.2.7), 30
412
Standard 1.0
Remote Office 9150