Issue
Online Messages on an SLI
Environment
I/NET site
Cause
Messages coming from the Sub Lan Interface (SLI)
Resolution
A door controller (DPU) has a limited amount of memory space available for storing individual records and messages. "Resident in DPU" individual records are given priority in storage: they are never discarded. Transient (non-resident) individual records and messages are stored on a space-available basis. If a communication outage between the SLI and the door controller causes the door controller's memory capacity to be reached, older records must be discarded as new messages continue to be generated. All records are discarded on a first-in, first-out (FIFO) basis, so that the remaining records are the most recent ones.
A "DPU queue ovflw" message will also be generated to warn that data was lost. Records are discarded in the following order:
- Transient individuals.
- Messages.
If there are no more transient individuals to discard, routine messages will be lost. When communications between the SLI and the door controller are restored, the contents of the door controller's queue (including the "DPU queue ovflw" message) will be delivered, freeing memory in the door controller. The SLI continually requests messages from its door controllers. Retrieved messages are queued within the SLI until they can be sent to appropriate host workstation(s).
When the SLI queue is full, it will continue to accept messages from door controllers (i.e., the SLI will not cause its door controllers to discard messages). With its memory queue full, the SLI will discard older messages as newer messages are received.
This ensures that the remaining records are the most recent ones. A "DCU queue ovflw" message will be generated to warn that data was lost. When communications between the SLI and the host PC are restored, the contents of the SLI's queue (including the "DCU queue ovflw" message) will be delivered, freeing memory in the SLI.
There is also a TPA-DALL-09-0001.00 that was written on this issue.
