Protocol Typ

ppp：Public-Private-Partnership

1.1 PPP frame header

The flag field F(Flag) in the header is specified as 0x7E (the symbol 0x indicates that the characters following it are represented in hexadecimal). the binary representation of hexadecimal 7e is 0111110) and the flag field indicates the beginning of a frame.

Address field A in the header is specified as 0xFF(i.e. 1111111).

The control field C in the header is specified as 0x03 (i.e. 0000011).

2 byte protocol field in header:

(1)When the protocol field is 0x0021, the information field of the PPP frame is the IP datagram.

(2)When the protocol field is 0xC021, the PPP frame information field is PPP Link Control Protocol LCP data.

(3)When the protocol field is 0x8021, the information field of the PPP frame is the control data of the network layer.

1.2 Information field portion of PPP frame

The length of the information field is variable and does not exceed 1500 bytes.

1.3 End of PPP frame

The first field (2 bytes) in the trailer is the frame check sequence FCS using CRC.

The flag field F(Flag) in the tail is specified as 0x7E (the symbol 0x indicates that the characters following it are represented in hexadecimal). the binary representation of hexadecimal 7e is 0111110) and the flag field indicates the end of a frame.

HDLC-Bit Oriented Synchronization Protocol: High Level Data Link Control