As shown in the Figure, the fields of a PPP frame are as follows:
- Flag-Indicates the beginning or end
of a frame and consists of the binary sequence 01111110.
- Address - Consists of the standard
broadcast address, which is the binary sequence 11111111. PPP does
not assign individual station addresses.
- Control - 1 byte that consists of the
binary sequence 00000011, which calls for transmission of user
data in an unsequenced frame. A connection-less link service
similar to that of Logical Link Control (LLC) Type 1 is provided.
- Protocol - 2 bytes that identify the
protocol encapsulated in the data field of the frame.
- Data - 0 or more bytes that contain
the datagram for the protocol specified in the protocol field. The
end of the data field is found by locating the closing flag
sequence and allowing 2 bytes for the frame check sequence (FCS)
field. The default maximum length of the data field is 1,500
bytes.
- FCS -
Normally 16 bits (2 bytes).
Refers to the extra characters added to a frame for error control
purposes.
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