Compare and contrast questions require you to explain the similarities and diffe

Question

Compare and contrast questions require you to explain the similarities and differences to get credit for your answer):

Chapter 10

1.What is the definition of a linear block code?

2. (2 parts )In a codeword, we add two redundant bits to each 8-bit word. Find the number of a. valid codewords & b. invalid codewords

3. If we want to be able to detect 2-bit errors, what should be the minimum Hamming distance?

4. In CRC, if the dataword is 5 bits and the codeword is 8 bits, how many 0s need to be added to the dataword to make the dividend? What is the size of the remainder? What is the size of the divisor?

5. In CRC, which of the following generators (divisors) guarantees the detection of an odd number of errors?

a. 10111 b. 101101 c. 111

6. Assume we are sending data items of 16-bit length. If two data items are swapped during transmission, can the traditional checksum detect this error? Explain your answer.

Chapter 11

7. Explain why flags are needed when we use variable-size frames.

8. Compare and contrast byte-oriented and bit-oriented protocols.

9. In a byte-oriented protocol, should we first unstuff the extra bytes and then remove the flags or reverse the process?

10. Compare and contrast flow control and error control.

11. Compare and contrast HDLC with PPP.

Explanation / Answer

1.If 2k codewords form a k-dimensional subspace of the vector space of all n-tupples over the field GF(2), then a block code C of length n with 2k codewords is called a linear code.

11.  HDLC generally operates at data link layer and also used for synchronous PPP connections.

HDLC functionality depends on the following:
• HDLC is a bit-oriented protocol.
• On transmitting end, it receives data from the application layer and delivers it to the receiving end on the other side of the application.
• On receiving end, it accepts data and transmits it to the high-level application layer.
• Both sides of the modules exchange control information, encoded into a frame.

PPP Protocol:

Point to point protocol is a byte-oriented protocol.
• It is operative at layer-2 and layer-3. PPP generally uses HDLC frame format at layer-2 and uses IPv4 and IPv6 formats at layer-3.

Other than IP, PPP supports other network layer protocols too. This is a main advantage of PPP.
• PPP also have a built-in security mechanism such as PAP(Password Authentication Protocol) and CHAP(Challange handshake authentication protocol).
• The crc-16 field is included in the frame which helps in error reduction.
• PPP uses same start and end flags used in HDLC frame which raises transparency problem.

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