Computer Networks

Tutorial #12

1. What are some of the characteristics of multi-access LANs which distinguish them from the point-to-point data links of last lecture?

2. What does CSMA/CD mean? CSMA/CD is sometimes referred to as the "polite dinner table" algorithm? Can you think of a reason for this?

3. What is interesting about the Ethernet/802.3 address format?

4. Ethernet/802.3 is a shared medium LAN technology. Does this pose any potential security risks? Explain.

5. In the lecture, it was stated that an Ethernet/802.3 collision occurs when two stations start to transmit at the same time. Discuss the meaning of the term at the same time as used in this context.

6. In slide 6 of today's lecture, it is stated that the key difference between Ethernet and IEEE 802.3 LANs is the meaning of the 16 bit "type" field (used as a "length" field in 802.3). In many LANS, Ethernet and 802.3 frames co-exist perfectly happily. How can a receiving station know whether to treat the field as a length or as a type?

7. The 10baseT configuration has captured the Ethernet market from thin wire. Discuss reasons why network planners and managers might prefer this technology.

8. Even though 10baseT Ethernet LANs are physically cabled as point-to-point networks, they are different to the point-to-point links of last lecture in a fundamental way. What is this?

9. Switching Hubs build a table which maps destination MAC addresses to port numbers. How do they build this table?

10. Research question: What is the historical origin of the difference between Ethernet and IEEE 802.3?

11. Opinion question: ATM is probably the dominant high-speed networking technology at present. What do you think is the particular attraction of ATM networks over other high-speed technologies, on the basis of the material presented in the lecture?