X = 4

Question 3 (25%). Consider that you are going to send the message OK?, where each character is encoded by 7-bit ASCII. (a) What is the bit stream of your message? (3%) (b) Suppose two-dimensional odd-parity check is used, with each character is considered as a block. Derive the bit stream to be transmitted. Show your steps. (8%) Now, your friend replies a message EASY, where each character is encoded by 7-bit ASCII. The message is protected by CRC using a polynomial below: 4th digit of your student ID number Odd Even CRC polynomial X4+ x2 X4+X (c) Calculate the CRC. Show your steps. (d) What is the bit stream to be transmitted? (e) Can CRC be used in forward error control? Justify your answer. (8%) (2%) (4%)