In this article the details of frame format is described. First you need to consider that the frames are different, there are different versions depending on which transport protocols and speeds of Ethernet. Analyze the IEEE 802.3 Ethernet frame and the Ethernet II Frame. (Developed by DIX).
IEEE 802.3 Ethernet is thus formed:
Pre | SFD | Destination | Source | Length/Type | Data/Filling | FCS
Pre: The preamble is a binary pattern of alternating zero and one, was used for Ethernet implementations of synch <= 10 Mbps Ethernet In new versions the preamble is not necessary but is maintained for compatibility. It consists of 7 octect.
SFD: Start of Frame Delimiter is a one octet field (1 byte) which marks the end of the preamble and then the timing information. Its bit pattern is 10101011.
Destination: It can be a unicast, multicast or broadcast.
Source: It’s usually a unicast MAC address of the host that has transmitted the frame.
Length / Type: This field can be used for two different purposes. If the value is less than 0 × 600 (1536), is used to explain the length of the frame (the length is used by LLC for the identification of the protocol). The type, however, indicates that the upper layer protocol (i.e., layer 3) receives data after the process Ethernet (encapsulation/decapsulation) was made. The length indicates the number of bytes of data.
Date / Filling: Can be of any length not to exceed the maximum frame size. The frame MTU is 1500 octets, so the data must not exceed this length. The content of this field is varied and a padding (filling) size is inserted immediately after random if the length is less than the minimum frame size to be between 64 and 1518 octecs.
FCS: frame check sequence. This field contains a CRC of 4 bytes created by the host sends the frame to be recalculated and the receiving host to check that there is no corrupted frames. A single bit corrupted from the beginning of the Target field to the end of the FCS field will cause the inevitable corruption of the frame and then the CRC is different. The control bits of the FCS is included in the main CRC, so you can not know in which field the error occurred.
Ethernet II is formed:
Pre | Destination | Source | Length | Data/Filling | FCS
The main difference from the version IEEE 802.3 is the aggregation dell SFD Preamble to the sequence of bits identical. The TCP/IP packets into Ethernet frames are encapsulation II.