Character stuffing !!

Question

i am understanding Character stuffing from an online resource !! 

It says " 

sing the special character of <DEL> and <STX> and <ETX> for start/end framing, the message: 

AB<DEL>C<STX><ETX>DE 

would be sent as (stuffed characters are underlined):

<STX>AB<DEL><DEL>C<DEL><STX><DEL><ETX>DE<ETX>...<STX>

" 
but they state that the problem with this method is 

" We can't use this method in situation like this when message is 

<DEL><STX>A<DEL><ETX> 

" 

why we can't do that ?? 

converting this <DEL><STX>A<DEL><ETX> to our codeword will give output something like this 

<STX><DEL><DEL><DEL><STX>A<DEL><DEL><DEL><ETX><ETX> 

where receiver will loose the sync ??

Answer 1

Character stuffing

Same idea as bit-stuffing, but operates on bytes instead of bits.

Use reserved characters to indicate the start and end of a frame. For instance, use the two-character sequence DLE STX (Data-Link Escape, Start of TeXt) to signal the beginning of a frame, and the sequence DLE ETX (End of TeXt) to flag the frame's end.

Problem: What happens if the two-character sequence DLE ETX happens to appear in the frame itself?

Solution: Use character stuffing; within the frame, replace every occurrence of DLE with the two-character sequence DLE DLE. The receiver reverses the processes, replacing every occurrence of DLE DLE with a single DLE.

Example: If the frame contained ``A B DLE D E DLE'', the characters transmitted over the channel would be ``DLE STX A B DLE DLE D E DLE DLE DLE ETX''.

Disadvantage: character is the smallest unit that can be operated on; not all architectures are byte oriented.