Assignment 4 

**** Do the following two activities at OnlineTextbookLearningCenter of only related materials 

(1) Take online quizzes of multiple choices.

(2) Try the multiple choices at the end of each chapter of textbook.  Selected solutions are founded at the site.

1. Compare and contrast the LLC and MAC sublayers.

2. Give an example of when autonomous error correction is appropriate.

3. Explain the various fields of an IEEE 802.3 frame.

4. Assume the CRC generator polynomial of x5 + x4 + x2 + 1 is used to provide error checking.  Use CRC algorithm to compute the bit stream that will be transmitted if a message 111000111000 is sent.

5. Do you think repeater's latency is less than or more than that of a bridge or a switch? Why?

6. What distinguishes a network component as being labeled a layer-1 or layer-2 device?

7. Data link protocols almost always put the CRC in a trailer, rather than in a header.  Why?

8. A 100 km long cable runs at the T1 data rate.  The propagation speed in the cable is 2/3 speed of light.  How many bits fit in the cable?

9. A group of N stations share 56-kbps pure ALOHA channel.  Each station outputs a 1000-bit frame on an average of once every 100 sec, even if the previous one has not yet been sent (e.g., the stations are buffered.)  What is the maximum value of N?

10. Consider the delay of pure ALOHA vs. slotted ALOHA at low load, which one is less? Explain your answer.

11. What is the baud rate of the standard 10-Mbps 802.3 LAN?

12. Consider building a CSMA/CD network running at 1 Gbps over a 1-km cable with no repeaters.  The signal speed in the cable is 200,000 km/sec.  What is the minimum frame size?

13. 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 (100 Mbps) 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?

14.  Imagine two LAN bridges.  The first bridge is faced with 1000 512-byte frames per second that must be forwarded.  The second is faced with 200 4096-byte frames per second.  Which bridge do you think will need the faster CPU?

15.  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?

16. Explain why in PPP the address field is set to HDLC broadcast address of 1111111.

17. Why is there a need for IPCP protocol for PPP?

18. Explain why WLANs can not implement CSMA/CD?  Explain the protocol for CSMA/CA?