Problem 1
Ethernet uses a preamble in combination with a byte count to separate the frames. What happens if a user tries to send data that contains this preamble?
Problem 2
The following character encoding is used in a data link protocol: A: \(01000111 \quad\) B: \(11100011 \quad\) FLAG: \(01111110 \quad\) ESC: 11100000 Show the bit sequence transmitted (in binary) for the four-character frame A B ESC FLAG when each of the following framing methods is used: (a) Byte count. (b) Flag bytes with byte stuffing. (c) Starting and ending flag bytes with bit stuffing.
Problem 5
You receive the following data fragment: A ESC FLAG A B A FLAG FLAG C B ESC FLAG ESC ESC ESC FLAG FLAG. You know that the protocol uses byte stuffing. Show the contents of each frame after destuffing.
Problem 6
You receive the following data fragment: 011001111100111101111101 . You know that the protocol uses bit stuffing. Show the data after destuffing.
Problem 7
One of your classmates, Scrooge, has pointed out that it is wasteful to end each frame with a flag byte and then begin the next one with a second flag byte. One flag byte could do the job as well, and a byte saved is a byte earned. Do you agree?
Problem 8
A bit string, 0111101111101111110 , needs to be transmitted at the data link layer. What is the string actually transmitted after bit stuffing?
Problem 9
An upper-layer packet is split into 10 frames, each of which has an \(80 \%\) chance of arriving undamaged. If no error control is done by the data link protocol, how many times must the message be sent on average to get the entire thing through?
Problem 11
To provide more reliability than a single parity bit can give, an error- detecting coding scheme uses one parity bit for checking all the odd-numbered bits and a second parity bit for all the even-numbered bits. What is the Hamming distance of this code?
Problem 12
Sixteen-bit messages are transmitted using a Hamming code. How many check bits are needed to ensure that the receiver can detect and correct single-bit errors? Show the bit pattern transmitted for the message 1101001100110101 . Assume that even parity is used in the Hamming code.
Problem 13
An 8-bit byte with binary value 10101111 is to be encoded using an even-parity Hamming code. What is the binary value after encoding?
