Rockwell Automation Ethernet Design Considerations Reference Manual - Manual (Page 30)

30 Rockwell Automation Publication ENET-RM002C-EN-P - May 2013
Chapter 2 Ethernet Infrastructure Components
Full-duplex Mode
Ethernet is based on Carrier Sense Multiple Access/Collision Detect (CSMA/
CD) technology. This technology places all nodes on a common circuit so they
can all communicate as needed. The nodes must handle collisions (multiple
devices talking at the same time) and monitor their own transmissions so that
other nodes have transmission time.
The data transmission mode you configure determines how devices transmit and
receive data.
Full-duplex mode eliminates collisions. Combined with the speed of the switches
available today, you can eliminate the delays related to collisions or traffic in the
switch. A a result, the EtherNet/IP network becomes a highly deterministic
network well-suited for I/O control:
• If you are autonegotiating, make sure you verify the connection.
• If you are forcing speed and duplex on any link, make sure you force at
both ends of the link. If you force on one side of the link, the
autonegotiating side always goes to half-duplex.
Transmission Mode Features
Full-duplex Deterministic
• Transmit and receive at the same time
• Transmit on the transmit pair and receive on the receive pairs
• No collision detection, backoff, or retry
• Collision free
Half- duplex Nondeterministic
• One station transmits and the others listen
• While transmitting, you do not receive, as no one else is transmitting
• If someone else transmits while you are transmitting, then a collision occurs
• Any Receive-while-Transmit condition is considered a collision