Flag A single byte that indicates the beginning or end of a frame. The flag field consists of the binary sequence 01111110.
Address A single byte that contains the binary sequence 11111111, the standard broadcast address. PPP does not assign individual station addresses.
Control A single byte that contains the binary sequence 00000011, which calls for transmission of user data in an unsequenced frame. A connectionless link service similar to that of Logical Link Control (LLC) Type 1 is provided. (For more information about LLC types and frame types, refer to Chapter 16, "Synchronous Data-Link Control and Derivatives. " )
Protocol Two bytes that identify the protocol encapsulated in the information field of the frame. The most up-to-date values of the protocol field are specified in the most recent Assigned Numbers Request for Comments (RFC).
Data Zero or more bytes that contain the datagram for the protocol specified in the protocol field. The end of the information field is found by locating the closing flag sequence and allowing 2 bytes for the FCS field. The default maximum length of the information field is 1,500 bytes. By prior agreement, consenting PPP implementations can use other values for the maximum information field length.
Frame Check Sequence
(FCS) Normally 16 bits (2 bytes). By prior
agreement, consenting PPP implementations can use a 32-bit (4-byte) FCS
for improved error detection.