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-   -   HDLC bit stuffing question (http://www.go4expert.com/forums/hdlc-bit-stuffing-question-t17559/)

ferrero 16May2009 13:30

HDLC bit stuffing question
 
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

SaswatPadhi 16May2009 14:20

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

Code:

Input String  = 01111001101111101111110100000010
Output String = 0111100110111110111110101000000010 ('0' bit inserted after five '1' bits)

Case 1 : Output received without error :
Code:

Received String  = 0111100110111110111110101000000010
Recovered String = 011110011011111011111101000000010

Case 2 : Output received with error at 16th bit :
Code:

Received String = 0111100110111111111110101000000010 (error bit in bold)
No string is recovered as more than 6 consecutive '1' bits are encountered

I hope this will help. :smile:

ferrero 16May2009 14:40

Re: HDLC bit stuffing question
 
thanks SaswatPadhi~! :happy::happy::happy:

SaswatPadhi 16May2009 15:19

Re: HDLC bit stuffing question
 
Quote:

Originally Posted by ferrero (Post 47950)
thanks SaswatPadhi~! :happy::happy::happy:

My pleasure :biggrin:

sathishvgowda 29Sep2011 15:19

Re: HDLC bit stuffing question
 
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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