1.3k views

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 ??

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.