There are two types of serial interface equipment available: Data Terminal Equipment (DTE) and Data Communications Equipment (DCE). The primary difference between DTE and DCE is the use of several pins on the connector. For example, DTE devices output on pin 2 and input on pin 3. DCE devices output on pin 3 and input on pin 2. You can connect a DTE interface directly to a DCE interface.
To connect either a DCE to a DCE, or a DTE to a DTE, use a null modem cable. A null modem cable allows equipment interfaces of the same type to be connected by swapping the appropriate input and output pins.
The serial ports for workstations and servers are all configured as DTE devices. Most terminals are also configured as DTE devices. Therefore, to connect a terminal to a workstation that has RS-232 or DB-9 connectors, use a null modem cable (if this connection does not work correctly, consult the documentation for your terminal to determine its requirements). To connect a modem to the workstation, use a cable that connects each pin of the serial port to the corresponding pin of the modem. No signals need to be swapped. Ensure that your cable is a straight connection before using it with your system. Connect other peripheral devices according to the configuration data provided with the device.
Silicon Graphics provides three special files that determine the signals that are used on each port. The special files beginning with ttyd are used for devices such as terminals; the files ttymX are used for modems that do not use hardware flow control; and ttyfX files are used for devices that can use hardware flow control on the RTS and CTS pins.