Data Frame

| - data frame

　　Data frame (Data frame), the protocol data unit is a data link layer,
　　which includes three parts: a frame header, a data portion, the end of the frame.
　　Wherein the header and trailer contain control information necessary,
　　such as synchronizing information, address information, error control information;
　　data part contains the data passed down the network layer, such as IP packets.
| - type data frames
　　at the transmitting end, the data link layer to the network layer data encapsulated in a frame have passed down,

　　　　　　　Then sent to link up;
　　At the receiving end, the data link layer data frame is received in and taken out to the network layer.
　　Different data link layer protocols corresponding to different frames, a variety of frames, such as PPP frame, MAC frames, etc.,
　　which are not the same specific format.
| - example of a data frame
　　following a MAC frame format as an example:
　　header MAC frame includes three fields. Destination address field two fields before are 6 bytes long and \

　　A source address field,
　　a destination address field contains a destination MAC address information, a source address field contains the MAC source address information.
　　The third field is a 2-byte type field, which contains the information on the sign to use what protocol layer,
　　for receiving an end portion of the data received from the MAC frame to the upper layer protocol.
　　eg: When the value of the Type field is 0x0800, the upper layer indicates it is the IP datagram;
　　　　if Type field is 0x8137, it indicates that the frame is sent over a Novell IPX.
　　　　Data portion of the MAC frame is only one field, a length between 46 to 1500 bytes,
　　　　the information contained is passed down the network layer data.
　　　　Frame end MAC frame is only one field is 4 bytes long,

　　　　Information contains the frame check sequence of the FCS
　　　　(cyclic redundancy check using the CRC code check)

| - Related distinction
　　　　packet (Packet) data unit is TCP / IP protocol communications transmission, generally known as "packets."
　　　　TCP / IP protocol is working in the third layer of the OSI model (the network layer), a fourth layer (transport layer), the
　　　　frame work of the second layer (data link layer). Contents transmitted by the content layer the next layer,
　　　　so that the LAN, "package" is included in the "frame" in. The so-called data frame (Data frame),
　　　　is a data link layer protocol data unit, which includes three parts: a frame header, a data portion, the end of the frame.
　　　　Wherein the header and trailer contain control information necessary, such as synchronizing information, address information,

　　　　Error control information;
　　　　data part contains the data passed down the network layer, such as IP packets.
| - frame format
　　　　frame format refers to the format of a frame in accordance with the provisions of different protocols.

　　　　Typically consists of "header + data" in two parts.
　　　　The main frame format Ethernet frame format, the data frame format, the IEEE 802.3 frame format, MAC frames, format.