User's Manual Part 2

11: Monitoring the Network
APCD-LM043-8.0 (DRAFT C) 169
which suggests that 4% of the radio traffic is used to retransmit packets, which is referred to in
this document as the Retransmission Rate.
From an operational point of view, it is important to keep the number of retransmissions to a
minimum since they reduce the total air time available and the total network throughput.
These calculations may appear tedious, but since all of the referenced statistics are available
through MIBs, SNMP management tools, such as SNMPc, can directly collect the statistics,
calculate the above metric, and track and report its value over time.
NOTE: The “stats summary” command displays similar calculations.
You can also monitor the MAC statistic “txPayloadsFailQueueTooLong” at the CCU to give an
indication of packet discards due to queue overrun. The MAC statistic
“lastQueueTooLongEUM” at the CCU indicates for which EUM the last packet was discarded.
That EUM can then be “watched” to determine how often discards occur and whether it is a
problem. Some discards may occur simply due to multiple concurrent downloads combined
with heavy system loading. If more than one EUM is having problems, the
“lastQueueTooLongEUM” statistic will change as discards occur.
11.2 CCU Receive Statistics
Similar to the case for CCU transmit statistics, there are several key CCU receive statistics
that you can use to monitor on-going performance of the CCU radio network. When the CCU
sends a directed poll to an EUM, it expects to get an acknowledgement. The following results
have been taken from a live CCU using the
<stats mac> command:
Table 30 Typical CCU Receive Statistic
Statistic Description Sample
A rxPktsDirected The number of packets received
correctly from all EUMs. These may
contain an ack.
409,730