ISRO CSE 2007 | Question: 24, ISRO CSE 2016 | Question: 67

Question

Bit stuffing refers to

• A. inserting a $0$ in user stream to differentiate it with a flag
• B. inserting a $0$ in flag stream to avoid ambiguity
• C. appending a nipple to the flag sequence
• D. appending a nipple to the use data stream

Comments

 

• Bit stuffing ek framing technique hai jo DLL mein use hoti hai.

• Jab data stream mein 5 consecutive '1's aate hain, toh ek extra '0' bit insert kiya jaata hai taaki flag pattern (e.g., 01111110) se confusion na ho.

• Receiver side pe, ye extra '0' bit detect karke remove kar diya jaata hai, original data restore karne ke liye.

• Ye technique HDLC, PPP, jaise protocols mein use hoti hai.

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Specifically, 

• HDLC → Bit Stuffing 
   
• PPP (byte-oriented framing) → Byte Stuffing

Answer 1

Bit stuffing refers to inserting a 0 in user stream to differentiate it with a flag.

Each frame begins and ends with a special bit pattern called a flag byte ex. 01111110.

Whenever sender data link layer encounters five consecutive ones in the data stream, it
automatically stuffs a 0 bit into the outgoing stream.

When the receiver sees five consecutive incoming ones followed by a 0 bit, it automatically
destuffs the 0 bit before sending the data to the network layer.

Option A is correct.

Comments

@ManojK hey! in the stuffed stream, you have written '000000' (6 0's) in the end, but not marked that extra 0 as red, is that a stuffing or a typing error by you?

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Hi i have a doubt, how does the receiver knows while un stuffing bits that the mentioned bits above are 1 or 0 in the original message.

Say sender sends a data, after five consecutive 1's a 1 is there and while stuffing it is changed to 0. But while un stuffing how does that receiver knows that it is 1 or 0 before stuffing it?

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hi...is this mandetory that all time we use 0 for bit stuffing

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Ya, that's also my doubt. If the flag stream contains 5 0's and then 1 how can we stuff an extra 0 in it. So, I think answer should be option d

Answer 2

Bit Stuffing refers to the insertion of non information bits into data.

Application:-

1.To Differentite the Frame delimator (Used for Synchronization purpose)From the original data.

2.For bringing bit streams that do not necessarily have the same or rationally related bit rates up to a common rate.

3.To fill buffers or frames.

https://en.m.wikipedia.org/wiki/Bit_stuffing