Data transfer with encoding
  RLL - Run Length Limited (Huffman coding)

  Encodes block of data bits on larger block of bits 
    to guarentee changes in signal level with in a limited span.

  Data is encoded so that the number or "run" of consecutive zeros is limited.

  Also limits number of consecutive one's to limit high frequency attenuation.

  Cost - Increases the number of bits needed.

   Generic example 
     
   Data   RLL 
          000 
          001 
   00     010   010
   01     011   011
          100 
   10     101   101
   11     110   110
          111 
   
   When combined as a stream of bits,
     At most 2 zeros or 4 ones next to each other.

   Implementations of real RLL encoding is more complex.

   Once data is encoded as RLL, any of the encoding methods may be used.