TDC 425
Homework #4
Summer I 2011
This assignment not accepted after June 30th 6:00pm
1a. In generic terms, how big is the remainder of a cyclic redundancy checksum (how many bits of remainder are added to the end of the original message)?
b. Specifically, how big is the remainder when using CRC-16? CRC-32?
2a. What kinds of errors can escape detection using parity? (single-bit, double-bit, etc)
b. What kinds of errors can escape detection using cyclic redundancy checksum (CRC)?
c. Assume that CRC-32 is the generating polynomial. What is the exact probability of each type of error that can escape detection?
3a. What bit is added to each of the following characters if even parity is used?
0110101
1001100
b. What bit is added to each if odd parity is used?
4. In a sliding window system with each byte numbered, Station A sends a packet with bytes numbered 801 to 900. If the packet arrives with no errors, how does Station B respond?
5. In a sliding window error control system, Station A sends a packet with bytes 501-700, followed immediately by a packet with bytes 701-900. Create a diagram of this error control scenario and show the response(s) that Station B will send if the second packet is lost in the network.
6. In a sliding window error control system, Station A sends a packet with bytes 501-700, followed immediately by a packet with bytes 701-900. Create a diagram of this error control scenario and show the response(s) that Station B will send if both packets arrive but there is a checksum error in the second packet.
7. Consider a CSMA/CD LAN with two workstations at the ends of a 1 km connection and with a data rate of 100 Mbps.
a. What is the time to send a frame of 1500 bits to another station, measured from the beginning of transmission to the end of reception? Assume a propagation speed of two-thirds the speed of light. Be careful to not mix meters with miles. (Hint: You need to calculate propagation timewhich is distance over velocity and add that result to data transfer time which is the length of the data frame over the data transmission rate.)
b. If two stations begin to transmit at exactly the same time, their packets will collide. If each transmitting station monitors the bus during transmission, how long before it notices a collision, in seconds? How many bits will be transmitted during this time? (First calculate the propagation time as you did in part a, then multiply by data transmission rate.)