User's Manual Part 2

168 APCD-LM043-8.0 (DRAFT C)
11: Monitoring the Network
The objective of the first level analysis of this data is to determine the relative amount of radio
traffic resulting from retransmissions. Ideally, the percentage would be 0. In practice, local
engineering limitations result in a certain normal level. Once this normal level is established,
the statistics can be used to monitor changes.
Since not all of these CCU transmit statistics are independent, you have to be careful when
interpreting and using results which are based on these statistics. For example, since
broadcast payloads are not acknowledged, the retry data is not relevant to these payloads,
and they have to be subtracted from the total. In addition, the
txPayloadsFailAssocDeleted
and the following payloads are never transmitted and should be subtracted from the total. The
calculations to do this are shown below:
Net Payloads sent through directed polls (see note) = B + C + D + E + F = 68,236
NOTE: Due to real-time issues (at any given time, some packets are
being processed or queued), the numbers often differ by the
small number of packets that are in queues.
The percentage of directed payloads that are delivered on the first transmission
= 66,001 / 68,236 = 97%
Similarly, the percentage of directed payloads not delivered on the first transmission, but
delivered on the second transmission
= 1,761 / (68,236 - 66,001) = 79%
It is generally a good indication if most payloads that fail on the first try are then successful
with only one retry.
The percentage of directed payloads that are not able to be delivered
= 102 / 68,681 = 0.15%
A very low undeliverable payload rate implies that user service has a high level of integrity,
and that the radio link is not significantly impacting higher-level TCP/IP applications.
The impact of the retransmission can be calculated by looking at the total number of
transmissions requiring acknowledgments:
= 1xB + 2xC + 3xD + 4xE + 4xF = 71,138.
Adding to this value the non-acknowledged broadcast payloads (
txPayloadsBCast = 445)
results in total txPayloads - 71,583.
A simple metric of overall sector link quality is the effective utilization of the channel, which can
be readily calculated as desired payloads transmitted/actual payloads transmitted, or:
(
B + C + D + E +F) / (71,138 - G + H + I + J + K + L)
= 68,236 / 71,127 = 96%