The timing of normal inbound frame transfer is shown in the following figure. This shows that Ethernet frame reception is proceeded by a preamble field. The IEEE 802.3-2008 specification (see clause 35) allows for up to all of the seven preamble bytes that proceed the Start of Frame Delimiter (SFD) to be lost in the network. The SFD is always present in well-formed frames.
Figure 1. GMII Normal Frame Reception
