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HDLC bit stuffing question

Discussion in 'Programming' started by ferrero, May 16, 2009.

  1. ferrero

    ferrero New Member

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    Hi guys,

    my first post here. I have a tutorial question and i am stuck. :nonod:
    Hope all the gurus here can help me pls?

    The question goes...


    Consider HDLC protocol.

    Apply the bit stuffing rule to the following data string and obtain the output string

    01111001 10111110 11111101 00000010

    B) What happens at the receiver if the trasmitted sequence is received without errors?


    C) What happens at thre receiver if the trasmitted sequence is received with a single bit error in the 16th transmitted bit




    Thanks in advance....:D
     
  2. SaswatPadhi

    SaswatPadhi ~ Б0ЯИ Τ0 С0δЭ ~

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    As much as I remember about Bit Stuffing, this should be answer to your question :

    Code:
    Input String  = 01111001101111101111110100000010
    Output String = 011110011011111011111[U]0[/U]101000000010 ('0' bit inserted after five '1' bits)
    Case 1 : Output received without error :
    Code:
    Received String  = 011110011011111011111[U]0[/U]101000000010
    Recovered String = 011110011011111011111101000000010
    Case 2 : Output received with error at 16th bit :
    Code:
    Received String = 011110011011111[B]1[/B]11111[U]0[/U]101000000010 (error bit in [B]bold[/B])
    No string is recovered as more than 6 consecutive '1' bits are encountered
    I hope this will help. :smile:
     
    Last edited: May 16, 2009
  3. ferrero

    ferrero New Member

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    thanks SaswatPadhi~! :happy::happy::happy:
     
  4. SaswatPadhi

    SaswatPadhi ~ Б0ЯИ Τ0 С0δЭ ~

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    My pleasure :biggrin:
     
  5. sathishvgowda

    sathishvgowda New Member

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    SaswatPadhi,
    We have device which PPP with bit stuffing,

    but we are observing 2-4 abort/CRC error packets for every 256 LCP packets when our device WAN Link to Pentas/CISCO routers.....

    Also, we could identify for which packet it giving aborts....

    Packet structure is as follows:-
    1 2 3 4 5 6 7
    FLG 1111 1111 0000 0011 1100 0000 0010 0001 0000 1001 0111 0101 0000 0000
    8 9 10 11 12 13 14
    0000 1000 1010 1010 1000 0000 1000 0111 1110 0010 1111 0111 1111 1000 FLG

    i.e., LCP packet structure is 14 bytes and last 2 bytes are FCS bytes...

    And also abort/crc errors are obsreverd in CISCO/pentas,
    when 13 & 14 contents are as follows :-
    13 14
    XXXX XXX1 1111 1XXX

    Kindly give your expertise advice on this...

    Thanks in advance,

    Rgrds,
    SathishV
     

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