Protocol Engine Output Pending Queue - BCPro - LIT-12011908 - General System Information - BCPro System - 4.0

MS/TP Communications Bus for the BCPro System Technical Bulletin

Product name
BCPro System
Document type
Technical Bulletin
Document number
Revision date

The BACnet® Protocol Engine has an output pending queue used to hold messages when slower communications links, such as MS/TP, are not able to keep up with the rate at which outgoing messages are generated. If this queue becomes too large, the time required to send a message becomes excessive, resulting in slow operation. When this slow operation occurs, applications begin to encounter errors and some devices may drop offline. Messages that are waiting are also counting down their APDU Timeout.

If the Protocol Engine output pending queue is in the trouble state or worse, reading the initial values at startup is delayed.

If the Protocol Engine output pending queue is critical, originated outgoing messages are discarded and the sending applications receive an error.