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The Point-to-Point (framing) protocol (PPP)

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• PPP: (point-to-point protocol) Another Byte-oriented framing method
  • Some PPP facts:

    PPP was based on a very polular data link layer called HDLC (High Level Data Link control) PPP was designed to replace an older protocol called SLIP (Serial Line Internet Protocol) SLIP was used to connect PCs to the Internet at home If you use DSL at home, then your Ethernet router uses PPP to communicate with the DSL modem.

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• Idle transmitter in PPP
  • If a node that is idle (= has no frame to send), will transmit the following empty frame:

    011111100111111001111110.... Flag Flag Flag

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• Frame transmission protocol in PPP
  • A node will transmit a frame as follows (= protocol):

    The flag sequence 01111110 (if it has not already transmitted a flag previously) A one byte address A one byte control code A two bytes protocol code User data Optional: one or more padding bytes two byte (16 bits) CRC check sum Flag

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  • The behavior of a sender using PPP is as follows:

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  • NOTE:

    The FLAG (01111110) character is the only special (reserved) character If the content in the header or body contains a FLAG byte, the FLAG byte is transmitted as: ESCAPE Flag (The ESCAPE in data is transmitted as ESCAPE ESCAPE !!!)

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  • More info:

    Wikipedia: click here