Homework Assignment 4

Due in class Thu October 5.

1. W & V Problem 3.4

2. W & V Problem 3.9

3. The maximum distance between two computers 
attached to a 10BaseT hub is 200m. Assume that
the propagation speed in twisted pairs is at
least 1.75 x 10^8 m/s. Assume that the hub takes
at most 0.1 us to detect a collision. What is
the maximum time between when a node starts
transmitting a packet and when it learns that the
packet has collided?

4. FInd the maximum data rate of a 10Mbs channel
using Ethernet as a function of packet length.

5. Ten thousand airline reservation stations are
competing for the use of a single slotted Aloha
channel. The average station makes 18 requests/hour.
A slot is 125 usec. What is the approximate channel
load?

6. Measurements of a slotted Aloha channel with an
infinite number of users show that 10% of the slots
are idle.

(a) What is the channel load G?
(b) What is the thoughput?
(c) Is the channel underloaded or overloaded?

7. A seven story office building has 15 adjacent
office per floor. Each office contains a wall
socket for a terminal in the front wall so the
sokets form a rectangular grid in the vertical
plane, with a separation of 4m between sockets
both horizontally and vertically. Assuming that
it is feasible 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) a star configuration with a single router in
the middle?

(b) an Ethernet?

(c) a ring network?

8. Two stations on an Ethernet are to transmit
long (multipacket) files. After each packet they
must contend for the next slot. What is the
probability that contention ends on round k and
what is the mean number of rounds per contention
period?