Homework #8 Solutions
cs349 -- Networks

Imagine that A is sending a packet to D.  Does C know
that that transmission is happening?  If so, how?  If not,
why not?

    It does know, because it heard D's CTS.

If C sends an RTS to B during that transmission,
would it interfere with the transmission?  Explain how C would know
whether it was OK or not.

	It would cause interference, and C knows it because
	it knows that the receiver is in range.

Imagine that some time in the future D is sending a message to
A.  Does C know that that transmission is happening?  If so, how?  If
not, why not?

     It does know, because it heard the RTS and it hears the frame.

If C sends an RTS to B during that transmission,
would it interfere with the transmission?  Explain how C would know
whether it was OK or not.

	It would not cause interference, because the listener is out
	of range, and C knows that because it did not hear the CTS.

Question 47 from the book

An IEEE 802.5 token ring has five stations and a total wire
length of 230m.  How many bits of delay must the monitor insert
into the ring?  Do this for both 4 Mbps and 16 Mbps; use a propagation
rate of 2.3 x 10^8.

   As an aside, this propagation rate is approximately right for
   the propagation of an electrical signal in a wire (about 2/3
   the speed of light).  It is worth noting, though, that the
   electrons themselves don't move anything like that fast
   (only a few meters per second of drift).

   Anyway, the token is 24 bits.  5 of them are in stations at any
   given time, so we have to figure out how many are on the wire.

   The propagation time is 230m / 2.3 x 10^8 m/s = 1 us

   At 4 Mbps that means there are 4 bits on the wire and
   24 - 5 - 4 = 15 bits in the monitor.

   At 16 Mbps there are 15 bits on the wire and only
   24 - 5 - 16 = 3 bits in the monitor.