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26 C2653M (6/07)
RJ-45 10BASE-T/100BASE-TX Port Status LED - Right (Duplex/Collision) (Continued)
Not lit Port is set to
10BASE-T
half-duplex
mode and no
collisions
are
detected.*
— If 10BASE-T half-duplex operation is
desired, no action is required.
If 10BASE-T half-duplex operation is not
desired, refer to the Setting 10BASE-T/
100BASE-TX Port Modes of Operation
section in this manual for information.
*A collision is a normal event on a half-duplex Ethernet link. A collision occurs when two or more
devices, referred to as stations, attempt to transmit at the same time on a shared physical medium.
Ethernet uses the CSMA/CD (Carrier Sense Multiple Access/Collision Detect) media access method by
which two or more stations share a common transmission medium. Using CSMA/CD, a station monitors
the medium and transmits a message in bit-serial form when it senses that no other station is
transmitting. If, after initiating a transmission, the message collides with that of another station, each
transmitting station then intentionally transmits for an additional predefined period to ensure
propagation of the collision throughout the system. To avoid another collision, each station waits a
random amount of time (backoff) before attempting to transmit again.
Excessive collisions occur when retransmission of a frame fails after 16 consecutive times and the
frame is dropped. Excessive collisions may indicate that the network is becoming congested.
Table C. Troubleshooting with Rear-Panel Indicators (Continued)
Indicator
Color Meaning Possible Cause Corrective Action