Digi makes many serial devices, some of which are DTE (PortServer TS, EtherLite, Connect/ConnectPort, Digi One, USB-to-serial), and others which are DCE (TransPort, PKG RF modems, XBIB interface boards).
In order to use the proper cable pin configuration to connect any serial port to another, you'll need to know whether the serial interface for each serial device is DTE or DCE in nature.
Data flow on DTE ports is as follows:
RI - Input
DSR - Input
RTS - Output
TXD - Output
RXD - Input
CTS - Input
DTR - Output
DCD - Input
DTE device - When connecting the serial ports of two DTE devices together (example: a terminal or printer to a Digi DTE serial port), remember inputs go to outputs. Connecting two inputs or two outputs does nothing.
DCE device - The data flow on DCE ports is opposite the flow of DTE ports. When connecting a Digi DTE serial port to a DCE device such as an analog or RF modem, connect like signals together (RXD to RXD, TXD to TXD and so on).
Signal meaning over color or number - It should be noted that signal name or meaning takes precedence over a wire's color or a pin number.
For example, both the Digi PortServer TS and EtherLite product lines use an RJ45 DTE serial interface, but because RJ45 is a non-standard serial interface (and we acquired the products through different means), each one has a unique RJ45 serial pinout (which itself would be different from the RJ45 serial interfaces of another manufacturer devices).