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11 Monitoring the Network
APCD-LM043-4.0 133
As with the CCU transmit statistics, the following sample calculations can be made using the
sample data from
Table 29 :
Total number of desired payloads = B + C = 44,718 + 2 = 44,720
This is also equal to:
(txPayloads1Ok + txPayloads2Ok + txPaylo txPayloads 4Ok +
txPayloadsFailRetry) = (36,889 + 5,216 + 1,489 + 553 + 573) = 44,720
NOTE: Due to real-time issues (the fact that at any given time, some
packets are being processed or queued), the numbers frequently
differ by the number of packets that are in queues.
NOTE: In the case of the EUM, most payloads are sent in response to
directed polls; however, a small number of payloads are sent in
response to random access polls.
The percentage of payloads that are delivered on the first transmission
= txPayloads1Ok / (B + C) = 36,889 / 44,720 = 82.5%
Similarly, the percentage of payloads that are not delivered on the first transmission but are
delivered on the second transmission
= txPayloads2Ok / (44,720 - 36,889) = 5,216 / 7,831 = 11.7%
The percentage of payloads that are not able to be delivered
= 573 / 44,720 = 1.3%
Since there are no broadcast or control payloads, the calculation of the Retransmission Rate
is fairly straightforward:
Retransmission Rate = (1 - desired payloads/actual payloads) x 100
= (1 - tx Data Payloads / txPayloads) x 100
= (1 - 44,718 / 56,293) x 100
= 21%
11.3.2 EUM Receive Statistics
Perhaps the most important receive statistic is the Receive Signal Strength Indicator (RSSI),
which gives a relative indicator of receive signal strength. Using the calibration table in the
PCF table, described in
Permanent Configuration File (CCU and EUM) on page 193, RSSI
can be used to determine the true receive signal level, in dBm. It is important to monitor this
statistic.
NOTE: Since the EUM can receive packets that are destined for other
EUMs, the EUM receive statistics are not as useful as the CCU
receive statistics. They are useful when the EUM is the only EUM
that is active, which is seldom the case after more than one EUM
have been activated.