Problem set 2 from chapter 2 (Physical Layer)

                  Problem 2.

                  A noiseless channel can carry arbitrrily large
                  amount of information, no matter the sampling rate.
                  Just send a lot of  data per sample. For 4KHz
                  channel,  make 8000 samples per second (Nyquist)
                  and if each sample is 16 bits, we have 128 kbps.
                  If each sample is 1024 bits, we have 8.2 Mbps.
                  You cannot do this with noise (Shannon's limit) 
                  Also take note of difference between Baud rate
                  and bit rate.

                  Problem 4.

                  The Shannon limit is 19.5 kbps.
                  The Nyquist limit is 6 kbps.

                  Problem 16.

                  Normally, the bits are sent over the line without  
                  any error correcting scheme in the physical layer.
                  with a cpu in each modem, it is possible to include
                  an error correcting code in layer 1 to greatly
                  reduce the  effective error rate seen by layer 2
                  The error handling by modems can be done transparently
                  to layer 2. Many modems now  have such error correction
                  feature built in. 

                  Problem 32.

                  Star:  Best case=2, average case=2, worst case=2
                  Ring:  Best=1, average=n/4, worst=n/2
                  full:  best=1, average=1, worst=1

                  Problem 41.

                  one paper - 80 square inches = 7.2 x 10 power 6
                  pixels and 2.88 x 10 power 7 bits. At 64 kbps,
                  the transmission takes 450 secs.  Fax machine
                  uses 1 bit per pixel, operate at 14.4 kbps and
                  transmitting a full page still takes 450 sec.
                  However, they are faster because they use run-
                  length encoding and most pages have lot of white      
                  space - 95% or so and the no. of bits per page     
                  with run-length encoding is much less.