Nortel Networks NN43001-563

144 ITG engineering guidelines

time=94ms

68 bytes from (10.3.2.7): icmp_seq=0 ttl=225

time=112ms

68 bytes from (10.3.2.7): icmp_seq=0 ttl=225

time=97ms

--- Richardson3 PING Statistics ---

8 packets transmitted, 8 packets received, 0% packet loss

round-trip (ms) min/avg/max = 94/96/112

The time ﬁeld displays the round trip time (rtt).

So that the delay sample results match what the IP Trunk 3.01 (and later)

node can experience, the PING host must be on a working LAN segment

attached to the router supporting the IP Trunk 3.01 (and later) node. The

selection of destination host is just as important, following these same

guidelines for the source host.

Set the size of the PING probe packets to 60 bytes, to approximate the

size of probe packets sent by IP Trunk3.01 (and later) used in determining

when new calls need to fall back.

Some implementations of PING support the -v option for setting the TOS.

IP Trunk3.01 (and later) allows the 8-bit DiffServ/TOS ﬁeld to be set to

any value speciﬁed by the IP network administrator for QoS management

purposes. For example, if a decimal value of 36 is entered in TM 3.1,

this is interpreted as TOS Precedence = Priority and Reliability = High. If

PING measurements are made on an intranet that uses prioritization based

on the TOS ﬁeld, the rttmeasured will be higher than the actual delay of

voice packets when the -v option is not used. See "Queue management"

(page 129).

Make note of the variation of rttfrom the PING output. It is from repeated

sampling of rttthat a delay characteristic of the intranet can be obtained.

In order to obtain a delay distribution, the PING tool can be embedded

in a script which controls the frequency of the PING probes, timestamps

them, and stores the samples in a raw data ﬁle. The ﬁle can then be to be

analyzed later using spreadsheet and other statistics packages. Determine

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

foreach IP Trunk3.01 (and later) site pair. If there are signiﬁcant ﬂuctuations

of trafﬁc in the intranet, it is best to include PING samples during the

intranet’speak hour. Fora more complete assessment of the intranet’s delay

characteristics, obtain PING measurements overa period of at least a week.

Nortel Communication Server 1000

IP TrunkFundamentals

NN43001-563 02.01 Standard

Release 5.5 21 December 2007