OSI/MHS Configuration and Management Manual

Troubleshooting Your OSI/MHS Subsystem
OSI/MHS Configuration and Management Manual—424827-003
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Unroutable Messages and Nondelivery Reports
Unroutable Messages and Nondelivery
Reports
This subsection describes message flow among OSI/MHS processes in general and
between the MR process and RTS in particular. An understanding of this message
flow can make it easier to identify routing problems. It is also the basis for message
tracking.
Problem Description
Each OSI/MHS process (RTS, MR, SC, MS, RS, and LO) consists of several functional
units (FUs). Each FU within an MHS process provides a specific set of related
functions, such as routing or P1 encoding. FUs communicate with each other by
passing messages known as internal data units (IDUs). Typically, an FU receives an
IDU, performs some work on that IDU, and then passes it to the next FU that needs to
process it.
Each MHS process contains a scheduler. The scheduler manages the FUs contained
within the process. The scheduler maintains message queues for each of the FUs
contained within the process, and it calls the entry points of a particular FU when a
message arrives for the FU to process. The scheduler provides inter-unit
communication, allowing IDUs to be passed between FUs within the process. The
schedulers in the MHS processes communicate with each other to provide interlayer
communication of messages between MHS processes.
The MR process has several FUs. One FU provides the interface with the MTS user
and is called the UA access manager. Another FU provides the interface with the RTS
and is called the MTA association manager. Another FU handles the interface with the
gateway and is the gateway access unit (GAU). The data flow across these interfaces
is in the form of inter-layer IDUs that can reference PDUs in the PDU store. The MS,
RTS, and gateway create PDUs in the PDU store before sending any interlayer IDUs.
In the case of the RTS, the message content is written directly to the PDU store as it
arrives from an adjacent MTA.
The data flow internal to the MR process takes the form of application IDUs. These
IDUs carry control information between the FUs within the MR process and, in most
cases, also refer to a message PDU (MPDU). The MPDU can be held in an encoded
form in the PDU store or it can be held in a memory-based, decoded form.
Logging of Message Processing Status
At certain points in the processing of a message, the MTA writes log records to the
PDU store, indicating how much processing has been done. These log records
provide checkpoints in the processing of a message and are read by the MTA recovery
manager to recreate application IDUs following a group failure. The log records also
indicate when a particular PDU has been completely processed and is no longer
required by any layer within the configuration.