Nortel ISDN Signaling Link, Description, Installation And Operation

Page: 115 / 380

ITG Engineering Guidelines Page 115 of 378
ITG Trunk 2.0 ISDN Signaling Link (ISL) Description, Installation and Operation
Some implementations of
ping
support the
Y option 1
for setting the TOS.
The ITG ISL Trunk allows you to set the 8-bit DiffServ/TOS field to any
value specified by the IP network administrator for QoS management
purposes. For example, if you enter a decimal value of 36 in MAT, this is
interpreted as TOS Precedence = Priority and Reliability = High. Note that if
the craftsperson made
ping
measurements on an intranet that does
prioritization (see “Queue management” on page 128) based on the TOS
field, the rtt measured will be higher than the actual delay of voice packets
when the
Y option is not used.
Notice from the
SLQJ output the variation of rtt. It is from repeated sampling
of rtt that a delay characteristic of the intranet can be obtained. In order to
obtain a delay distribution, the
SLQJ tool can be embedded in a script which
controls the frequency of the
SLQJ probes, timestamps and stores the
samples in a raw data file. The file can then be to be analyzed later using
spreadsheet and other statistics packages. You can check if the intranet's
network management software has any delay measurement modules which
can obtain a delay distribution for specific site pairs.
Delay characteristics vary depending on the site pair and the time-of-day. The
assessment of the intranet should include taking delay measurements for each
ITG site pair. If there are significant fluctuations of traffic in the intranet, it is
best to include
SLQJ samples during the intranet's peak hour. For a more
complete assessment of the intranet's delay characteristics, obtain
SLQJ
measurements over a period of at least a week.
Measure end-to-end packet loss
The
SLQJ program also reports if the ICMP packet made its round trip
correctly or not. In fact use the same
SLQJ host setup to measure end-to-end
error, and as in making delay measurement, use the same packet size
parameter.
Sampling error rate, however, requires taking multiple
SLQJ samples (at
least 30 to be statistically significant). Thus, obtaining an error distribution
requires running
SLQJ over a greater period of time. The error rate statistic
collected by multiple
SLQJ samples is called packet loss rate (PLR).
1. Within the 8-bit TOS field are 4 TOS bits from bits 4 to 7, which would be 0010 binary or 2 decimal