IBM 5000 - Manual (Page 94)

Management Port C
Your server has a dedicated systems management I/O port. This port can be used
to attach a modem that is dedicated to communication with the
system-management processor.
The connector on the back of the server and the pin-number assignments are the
same as for the serial ports.
1 5
6 9
Table 4 on page 83 shows the pin-number assignments for the serial port
connectors. The pin-number assignments conform to the industry standard.
84 Netfinity 5000 Server Hardware Information and Procedures