Sketch a space-time diagram of an Ethernet-type cable network.  Assume the bus 
segment has unit length and that the signal propagation speed through the 
medium is one (i.e., 1 unit of length per unit of time), and the data rate on 
the medium is also one (i.e., a frame of size 1 unit takes 1 unit of time to 
transmit).  Stations A, B and C are located 0.25, 0.499, and 0.75 units from 
the left of the cable.  There are no other stations.  The medium is quiet at 
t=0.  Stations follow the IEEE 802.3 (1-persistent CSMA/CD) protocol, but 
they never retransmit frames that have collided.  Frames are 2 units long.  
Stations A, B, and C receive frames from their higher layers at times t=0, 
0.25, and 0.25, respectively.

(a)	Draw the beginning and end of station transmissions and other 
interesting events as they propagate through the medium.  Label events on the 
diagram.

(b)	At time t=1 every location on the bus is busy.  At what point in 
(space,time) the channel becomes idle for the first time after time t=1?

(c)	At what point in time the channel becomes idle from one end to the other 
for the first time after time t=1?

(c)	Which stations succeed in transmitting their frames?