The timing of normal inbound frame transfer is illustrated in This Figure. This shows that Ethernet frame reception is preceded by a preamble field. The IEEE 802.3-2012 Specification [Ref 2] (see clause 35) allows for up to all of the seven preamble bytes that precede the Start of Frame Delimiter (SFD) to be lost in the network. The SFD is always present in well-formed frames.