University of Kansas
Electrical Engineering & Computer Science
1. Perform the bit stuffing procedure for the following binary sequence: 1100011111110111111101001.
2. Perform bit de-stuffing for the following sequence: 11101111101111100111110.
3. Consider the various combinations of communication channels with bit rates of 1 Mbps and 1 Gbps over links that have roundtrip times of 1 msec and 100 msec.
a) Find the delay-bandwidth product for each of the combinations of speed and distance.
b) Suppose 16-bit sequence numbers (n=16) are used to transmit blocks of 10,000 bits over the above channels. How long does it take for the sequence numbers to wrap around, that is, to go from 0 up to 2**n?
c) Now suppose the 16-bit sequence numbers (n=16) are used to count individual transmitted bytes. How long does it take for the sequence numbers to wrap around?
4. Three possible strategies for sending ACK frames in a Go-Back-N setting are as follows: send an ACK frame immediately after each frame is received, send an ACK frame after every other frame is received, and send an ACK frame when the next piggyback opportunity arises. Which of these strategies are appropriate for the following situations?
a) An interactive application produces a packet to send each keystroke from the client; the server echoes each keystroke that it receives from the client.
b) A bulk data transfer application where a server sends a large file that is segmented in a number of full-size packets that are to be transferred to the client.
5. Consider a 2 Mb/s link and with a one-way propagation delay of 4.5 ms.
a) Find the efficiency for Stop-and-Wait ARQ if the frame size is 4600 bits and 26,600 bits.
b) Repeat part a) for a 9.5 ms one-way propagation delay.
c) Use Stop-Wait-Efficiency-Trade-offs to check your a)-b) answers.
6. Consider a 2.5 Mb/s link and with
a) For a a one-way propagation delay of 6 ms find the efficiency of a sliding window Go-Back-N ARQ if 3-bit sequence numbering is used with frame sizes of 2000 bits, 4000 bits and 6000 bits .
b) Repeat part a) for a 2 ms one-way propagation delay.
c) Repeat part a) for a 10 ms one-way propagation delay.
d) Use Sliding Window Efficiency Trade-offs to check your a)-c) answers. Also see the Extend Model of Sliding window protocol.
7. A sliding window Go-Back-N ARQ protocol is used for a 2 Mb/s link with a one way propagation delay of 6 ms. The frame size is 2000 bits.
a) How many bits are needed in the sequence number to achieve 100% efficiency?
b) What window sizes will limit the senders rate to about 1.2 Mb/s and 800 kb/s?
c) Use Sliding Window Efficiency Trade-offs to check your a)-b) answers.
8. Explain the role of all of the protocol fields in an HDLC frame.
9. Traffic into a token bucket is constant length packets of length 1000 bits. The token arrive rate is 100 tokens/sec and the token buffer can hold 5 tokens. Packets not conforming to the average rate and maximum burst size are dropped.
a) What is the average rate in b/s leaving the token bucket?
b) What is the maximum burst size in bits for traffic leaving the token bucket?
10. What is the advantage of using a selective repeat ARQ?