In the Ethernet, which field is actually added at the physical layer and is not part of the frame.
preamble and SFD use as physical layer header
AnilGoudar The layers work in order. Any message received by a host will pass through like this: $PL\rightarrow DLL\rightarrow NL\rightarrow TL\rightarrow AL$
Ethernet frame is not "formed" at DLL, but rather DLL attaches some stuff to the bit-streams arriving through PL and calls that a frame.
The first field(Preamble) of 802.3 frame contains 7 bytes of alternating 0s and 1s that alerts the receiving system to the coming frame and enables it to synchronize its input timing. Preamble is added at the physical layer and is not part of the frame.