Definition (1):
Start frame delimiter (SFD) is a field in the Ethernet 802.3 frame that defines the beginning of the packet.
Definition (2):
“An Ethernet packet starts with a seven-octet preamble and one-octet start frame delimiter (SFD).” The preamble includes a 56-bit pattern of alternating 1 and 0 bits, which permits devices on the network to smoothly synchronize their receiver clocks, giving bit-level synchronization. It comes after the SFD to give byte-level synchronization and to indicate a new frame of incoming.
Definition (3):
An Ethernet frame begins with a preamble followed by the start frame delimiter (SFD). The real frame data begins after the SFD. All Ethernet packets begin with the same SFD which is followed by data specific to the specific frame.
Each Ethernet frame begins with a preamble and then SFD. SFD is a specific 8-bit (one-byte) pattern marking the end of the preamble and is an Ethernet packet’s first field, indicating the Ethernet frame’s beginning. It shows or represents the beginning of a transmission frame. It indicates that a new frame is coming. The SFD comes immediately after the destination MAC address.