| |
|
| 1. |
Six stations, A through F, communicate using the MACA protocol.
Is it possible that two transmissions take place simultaneously?
Explain your answer. |
| 2. |
A seven-story office building has 15 adjacent offices
per floor. Each office contains a wall socket for a terminal
in the front wall, so the sockets form a rectangular grid
in the vertical plane, with a separation of 4 m between
sockets, both horizontally and vertically. Assuming that
it is feasible to run a straight
cable between any pair of sockets, horizontally, vertically,
or diagonally, how many meters of cable are needed to connect
all sockets using
- a star configuration with a single router in the middle?
- an 802.3 LAN?
For each configuration, what is the maximum distance between
any two computers. |
| 3. |
Two CSMA/CD stations are each trying to transmit long (multiframe)
files. After each frame is sent, they contend for the channel,
using the binary exponential backoff algorithm. What is the
probability that the contention ends on round k, and what
is the mean number of rounds per contention period? |
| 4. |
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? |
| 5. |
An IP packet to be transmitted by Ethernet is 60 bytes long,
including all its headers. If LLC is not in use, is padding
needed in the Ethernet frame, and if so, how many bytes? |
| 6. |
Suppose that an 11-Mbps 802.11b LAN is transmitting 64-byte
frames back-to-back over a radio channel with a bit error
rate of 10-7. How many frames
per second will be damaged on average? |
| 7. |
Give two reasons why networks might use an error-correcting
code instead of error detection and retransmission. |
| 8. |
Briefly, describe the difference between store-and-forward
and cut-through switches. |
| 9. |
Store-and-forward switches have an advantage over cut-through
switches with respect to damaged frames. Explain what it is. |
| 10. |
A 1-km-long, 10-Mbps CSMA/CD LAN (not 802.3) has a propagation
speed of 200 m/�sec. Repeaters are not allowed in this system.
Data frames are 256 bits long, including 32 bits of header,
checksum, and other overhead. The first bit slot after a successful
transmission is reserved for the receiver to capture the channel
in order to send a 32-bit acknowledgement frame. What is the
effective data rate, excluding overhead, assuming that there
are no collisions? |
| |
|
| |
|
