Error Control and Data Compression

Question 1

What is the purpose of error control in data communication?

Answer 1

Error control ensures that data sent over a network is received accurately and intact. It detects and, in some cases, corrects errors caused by noise or interference during transmission.

Question 2

What are the two main types of error control techniques?

Answer 2

1. Forward Error Correction (FEC)
2. Feedback Error Control (ARQ)

Question 3

What is Forward Error Correction (FEC)?

Answer 3

FEC adds redundant data (error-correcting codes) to messages before transmission so the receiver can detect and correct errors without needing retransmission.

Question 4

What is Feedback Error Control?

Answer 4

Feedback Error Control relies on the receiver to detect errors and request retransmission from the sender using acknowledgment (ACK) and negative acknowledgment (NAK) signals.

Question 5

What is a parity bit and how does it work?

Answer 5

A parity bit is an extra bit added to data to ensure that the total number of 1s is even (even parity) or odd (odd parity). It can detect single-bit errors but not correct them.

Question 6

What are linear block codes used for?

Answer 6

Linear block codes use mathematical formulas to generate check bits that help detect and correct multiple-bit errors. Examples include Hamming and Reed-Solomon codes.

Question 7

What is Cyclic Redundancy Check (CRC)?

Answer 7

CRC uses polynomial division to generate a checksum. The receiver recalculates the checksum and compares it to the received value to detect errors.

Question 8

What is ARQ (Automatic Repeat Request)?

Answer 8

ARQ is a feedback error control method where the receiver sends a NAK for corrupted data, prompting the sender to retransmit the data.

Question 9

What is HDLC in the context of error control?

Answer 9

HDLC (High-Level Data Link Control) is a protocol that uses error detection with sequence numbering and flow control to ensure reliable data transfer.

Question 10

What is data compression and why is it used?

Answer 10

Data compression reduces the size of data to save bandwidth and storage space, improving transmission speed and efficiency.

Question 11

What is Huffman coding?

Answer 11

Huffman coding is a lossless compression technique that assigns shorter codes to frequently occurring symbols and longer codes to rare ones to reduce average data size.

Question 12

What are the steps involved in Huffman coding?

Answer 12

1. Calculate frequency of characters
2. Build a priority queue
3. Construct a Huffman tree
4. Generate binary codes
5. Encode and compress the data

Question 13

What is dynamic Huffman coding?

Answer 13

Dynamic Huffman coding builds the Huffman tree during the encoding process, adapting to data patterns on the fly. It’s better for unknown or changing data sets.

Question 14

In what scenarios is error control more important than compression?

Answer 14

Error control is critical in noisy or unreliable environments like satellite or wireless communication where accurate delivery is more important than speed.

Question 15

In what scenarios is data compression more important than error control?

Answer 15

Compression is prioritized in bandwidth-limited situations like file storage, mobile data transfer, and streaming where speed and size efficiency matter most.

Question 16

Can error control and data compression be used together?

Answer 16

Yes, compressed data can be protected using error control methods to ensure both efficient and reliable communication.