The following figure depicts the two mPacket formats. Packet (a) is used for express packets, a complete preemptable packet, or an initial fragment of a packet. Packet (b) is a continuation packet. The SMD field replaces the SFD field of a normal Ethernet frame and is used to indicate which mPacket format is in use. For more information, see IEEE 802.3-2018.
Figure 1. Preemption Header