Page 108 of 378 ITG Engineering Guidelines
553-3001-202 Standard 1.00 April 2000
QoS Evaluation Process OverviewThere are two main objectives when dealing with the QoS issue in an ITG
network: (1) to predict the expected QoS, (2) to evaluate the QoS after
integrating ITG traffic in to the in tr anet . Th e p roces s f or ei ther cas e i s s imil ar,
one is without ITG traffic and one is with. The fine difference between them
will be discussed at an appropriate place.
In the process, it is assumed that the Ping program is available on a Window
95 or NT PC, or some network management tool whic h can c oll ect dela y and
loss data that is accessed to the T-LAN connecti ng to the Rout er goi ng out to
the Intranet:
1Use ping or equivalent tool to collect round-trip delay (in ms) and loss
(in%) data.
2Divide the delay by 2 to approximate one-way delay, ad d 93 ms to adjust
for ITG processing and buffering time.
3Look up a QoS chart (Figure 5,6,7) or Table24 to predict the QoS
categories (excellent, good, fair or poor).
4If a customer wants to manag e the QoS in a mo re deta iled fa shion, h e/she
can re-balance the values of delay compared to loss by adjusting ITG
system parameters, such as preferred codec, payload size, routing
algorithm, etc. to move resulting QoS among different categories.
5If the QoS objective is met, repe at the process periodically to make sure
the required Qo S is maintained.
Set QoSThe users of corporate voice and data services expect these services to meet
some perceived quality of service (QoS) which in turn influence network
design. The goal is to design and allocate enough res ource s in the netwo rk to
meet users’ needs. QoS metrics or parameters are what quantifies the needs
of the “user” of the "service".
In the context of a Meridian 1 and ITG system, Figure14 on page 109 shows
the relationship between users and services:
From the diagram it can be seen t h at there are two interfaces th at the
technician needs to consider.