IBM ThinkPad 755CX Manual page 89

Communicating with the Infrared Port
During communication with rear infrared ports, the infrared ports
must face directly with each other at a communicating distance.
It is recommended that the communicating ThinkPad computers
use their rear infrared port to communicate with each other.
When communicating between a front infrared port and an
infrared port on another computer, the infrared ports on the
computers must face directly each other at a communicating
distance.
Chapter 3. Operating Your Computer
73