QTAM was an alternative to the lower level Basic Telecommunications Access Method (BTAM).
[1]: p.8 QTAM was succeeded by TCAM which provided roughly similar facilities, but was not supported under DOS.
The MCP handles communications with the terminals, identifies input messages and starts MPPs to process them as required.
These macros define the lines and terminals comprising the system, the datasets required, and the procedures used to process received and transmitted messages.
[1]: pp.31-93 The MPPs, incorporating logic to process the various messages, are supplied by the installation, and use standard OS/360 or DOS/360 data management macros OPEN, CLOSE, GET, and PUT.