Control frames are a special type of Ethernet frame defined in clause 31 of the IEEE 802.3 standard. Control frames are identified from other frame types by a defined value placed into the length/type field (the MAC Control Type code). The following figure illustrates control frame format.
A Pause Control frame is a special type of Control frame identified by a defined value placed into the MAC Control opcode field.
The MAC Control Parameter field of the Pause Control frame contains a 16-bit field that contains a binary value directly relating to the duration of the pause. This defines the number of pause_quantum (512-bit times of the particular implementation). At 1 Gbps, a single pause_quantum corresponds to 512 ns. At 100 Mbps, a single pause_quantum corresponds to 5,120 ns, and at 10 Mbps, a single pause_quantum corresponds to 51,200 ns.