As most of you have said, In the waterfall model each sterp 
is frozen before the next step. that is the requirements 
are frozen before the design starts, and once the design is 
frozen the coding starts etc. But what will the testing 
team do till then?????
  In V model, based on the requirements the System test 
cases are prepared, and based on the HLD (High level 
document)the Integration Test cases are prepared, and based 
on the LLD(Lowlevel document)the Integration Test cases are 
prepared. and then the coding is done. once coding is 
completed, unit, integration and system testing happens in 
the sequence.