I/O modules have link, activity, and speed LEDs (LNK/ACT and SPD, respectively) that indicate the state of a physical connection or traffic on a port. Port LEDs glow when the port senses an electrical or optical signal, detects a negotiated link speed, or both. Each port has its own LED(s), and the information displayed by the LEDs differs depending on the type of I/O module. Refer to: