Specifications

5-1
Chapter 5
Ethernet Media Access Method
Ethernet, as stated in Chapter 1, uses a method of access control known as Carrier Sense Multiple
Access with Collision Detection, or CSMA/CD. Access to the network media is controlled by the lower
half of the Data Link Layer called Media Access Control, or MAC. The following chapter describes the
operation of the Ethernet MAC.
Clean Frame Transmission
The following determines the process that an Ethernet station goes
through in a clean frame transmission over the network.
A station wanting to transmit first listens to the communication channel to
see if any other station is transmitting. If a carrier is sensed (another
station is transmitting), the station waits a random length of time, and
then listens to the communication channel again. If no other station is
transmitting, the station begins frame transmission.
During frame transmission, the station continuously monitors the bus. As
long as the monitoring shows there is no other station transmitting on the
cable, the frame transmission continues until the transmission is complete.
Once the frame transmission is complete, the station is quiet for 9.6 µs to
allow for the required interframe gap. After 0.6 µs into the interframe gap,
the transceiver is given a 1.4 µs window to test its collision detect circuitry
(see Figure 5-1).