# Practice Final Exam CS4514

The questions are based on material presented in class and reading material from the text.

Give brief answers to the following questions:

1. A LAN uses Mok and Ward's version of binary countdown. At a certain instant, the ten stations have the virtual station numbers 8, 2, 4, 5, 1, 7, 3, 6, 9, and 0. The next three stations to send are 4, 3, and 9, in that order. What are the new virtual station numbers after all three have finished their transmissions?

2. In a token ring the sender removes the frame. What modifications to the system would be needed to have the receiver remove the frame instead, and what would the consequences be?

3. A 4-Mbps token ring has a token-holding timer value of 10msec. What is the longest frame that can be sent on this ring?

4. Given the below figure:

Assume a 802.6 MAN. Which stations wants to transmit and who do they want to transmit to? Give a range of stations, if necessary.

5. Ethernet frames must be at least 64 bytes long to ensure that the transmitter is still going in the event of a collision at the far end of the cable. Fast Ethernet has the same 64 byte minimum frame size, but can get the bits out ten times faster. How is it possible to maintain the same minimum frame size?

6. If delays are recorded as 8-bit numbers in a 50-router network, and delay vectors are exchanged twice a second, how much bandwidth per (full-duplex) line is chewed up by the distributed routing algorithm? Assume that each router has three lines to other routers.

7. Figure 5-27 shows four input characteristics for a proposed flow specification. Imagine that the maximum packet size is 1000 bytes, the token bucket rate is 10 million bytes/sec, the token bucket size is 1 million bytes, and the maximum transmission rate is 50 million bytes/sec. How long can a burst at maximum speed last?

8. In our example transport primitives of Figure 6.3, LISTEN is a blocking call. Is this strictly necessary? If not, explain how a non-blocking primitive could be used. What advantage would this have over the scheme described in the text?

9. Imagine that a two-way handshake rather than a three-way handshake were used to set up connections. In other words, the third message was not required. Are deadlocks now possible? Give an example or show that none exist.

10. Datagram fragmentation and reassembly are handled by IP and are invisible to TCP. Does this mean that TCP does not have to worry about the data arriving in the wrong order?

11. If the TCP round-trip time, RTT, is currently 30 msec and the following acknowledgements come in after 26, 32, and 24 msec, respectively, what is the new RTT estimate? Use alpha = 0.9.