Homework 4 - Chapters 4 and 5

1. Explain why Manchester encoding cannot be used for Gigabit and Fast Ethernet. What encoding methods are used on twisted pair for each instead?
2. With Gigabit Ethernet, it is strongly recommended to use switches so that stations can turn off CSMA/CD and use full-duplex communication. However, for backwards compatability reasons, hubs are allowed on the LAN, which forces the use of CSMA/CD for the hub segment. How does Gigabit Ethernet handle the problem of minimum frame size when CSMA/CD mode is in use?
3. Under what circumstances might two or more wireless stations using MACA contention resolution transmit at the same time?
4. Would it be possible for any of the 802.11 protocols to use CSMA/CD (like Ethernet) instead of CSMA/CA for channel contention? Explain why or why not.
5. Assume an 802.11g is transmitting 128 byte frames back-to-back at its maximum rate of 54Mbps. If each bit is flipped with a probability of 1x10^-6, how many frames per second will be damaged on average?
6. A common "WiFi" setup is to have an 802.11 access point plugged in to an Ethernet LAN. Explain what the access point has to do to handle the transition between the Ethernet and 802.11 halves of the LAN.
7. Can a Bluetooth device be in multiple piconets at once? If so, can it act as master in more than one piconet?
8. When using a spanning tree algorithm to determine the topology for bridges, why might one leave bridges in place that are not used in the current spanning tree?
9. Do virtual circuit subnets need to use a routing algorithm that finds a path from any source to any destination? If so, at what point during a virtual circuit connection would this algorithm be needed?
10. Under what circumstances might a packet be delivered to the wrong destination or get lost in transit at the network layer?