physical media attachment (PMA)
The physical medium access( PMA) is a functional sublayer of the layer model that interfaces between the physical coding sublayer( PCS) and the physical medium dependent( PMD). The PMA sublayer performs a number of transmission and control functions, such as collision detection, clock recovery, reset, transmit, receive, carrier sense, linkintegrity, Jabber, align, and clock recovery.
With the Transmit function serial bit streams are sent over the transmission medium. It must be ensured that only a maximum of two full bit cells are lost. Already the second transmitted bit should correspond to the specified conditions with regard to the time and level behavior. The delay occurring between the MAU interface and the cable during the transmission of bits must not exceed half a bit time.
The Receive function is used to receive serial bit streams. When transmitting data packets, it must be ensured that a maximum of five full bit cycles are lost. Already the second transmitted bit should meet the specifications.
The collision function is used to detect collisions on the cable. If a collision occurs, the Medium Attachment Unit (MAU) transmits the Signal Quality Error( SQE). The SQE signal is represented by a frequency equal to half the bit rate.
The optional monitor function allows the transmit function to be turned off. However, the collision and the receive function remain unchanged.