User's Manual

APCD-LM043-4.0 127
11 Monitoring the Network
Although there are a large number of detailed statistics available for the various data handling
applications in the CCU (refer to Appendix H on page 223 for a complete list), there are only a
few that are key for monitoring system performance on an on-going basis. These statistics are
described in detail in the material below.
11.1 CCU Transmit Statistics
As described in MAC Layer (Polling MAC) on page 36, the MAC continuously transmits polls
to the EUMs. These polls can contain specific user data directed to the EUM or the PC
connected to the EUM, control data directed to the EUM, broadcast data directed to all EUMs,
or empty polls, which containing no information data.
In an ideal system, all data transmitted would be received error free by the EUMs, and no re-
transmissions would be required. In the real world, unfortunately, low signal conditions,
interferers, system engineering problems, and equipment malfunction can result in the need to
retransmit data over the radio link. These retransmissions, which are key to maintaining data
integrity for the end user, come with the trade-off of reduced network capacity.
Statistics reported by the CCU can assist in identifying when retransmissions are occurring
and at what rate they are occurring. They can also be used to troubleshoot the cause of
retransmissions.
The statistic txPayloads gives the total number of transmitted payloads, consisting of
• user data received by the CCU Ethernet port, and transmitted over the radio network,
• user data received from an EUM, that is “switched” to the CCU radio port for
transmissiontoanotherEUM,
• MAC control data,
• broadcast data, and
• data retransmitted because it was not acknowledged by an EUM and is assumed lost.