Specifications

Packet Involved in a Collision
5-2 Ethernet Media Access Method
Figure 5-1. Ethernet Interframe Spacing
During this time, the station will see the Signal Quality Error (SQE) test
signal on its collision detection. When the station sees this signal during
the 1.4 µs window, it is informed that the transceiver collision detect
circuits are working properly and if a collision occurred, it would be
notified.
After the remainder of the 9.6 µs interframe gap is complete, the station is
able to start the transmission process again by first listening to see if the
cable is available.
Signal Quality Error Test
The SQE (Heartbeat) is only generated by a transceiver and is only seen by
the host device that is connected to that specific transceiver. The SQE does
not appear on the network bus. It is a signal from a transceiver to its
associated station simply to inform the station that the transceiver’s
collision detection is working properly.
Packet Involved in a Collision
Because of propagation delays in the network, it is possible for two
stations to simultaneously find the bus available, in which case both
stations will begin transmitting frames. When these signals meet on the
cable, a collision occurs. These two signal voltages add together and
increase the voltage level on the cable, which is sensed by the transmitting
transceivers. The transceiver then sends a collision signal to the host
station, all while it is still transmitting the packet. If the station is not still
transmitting the packet, there is a problem in the design of the network,
and it does not meet IEEE 802.3 specifications.
Data Packet
Interframe Gap
9.6 µs
.6 µs
1.4 µs
2 µs
SQE Test
1913-11