v model is nothing but a erification and validation. 
whenever the requriments is ready at the same time the 
validation is also going. cheking paralell to customer 
reqriments

The answer told by chandra is wrong. the question was asked 
for SDLC model, the V model is one of the type of SDLC.

The answer posted by chandra is for the Question V&V

The V-model is a sequential path of execution of processes.
 Each phase must be completed before the next phase begins.
 Testing is emphasized in this model more so than the
waterfall model though.  The testing procedures are
developed early in the life cycle before any coding is done,
during each of the phases preceding implementation.

ADVANTAGES
Simple and easy to use. 
Each phase has specific deliverables. 
Higher chance of success over the waterfall model due to the
development of test plans early on during the life cycle. 
Works well for small projects where requirements are easily
understood.

DISADVANTAGES
Very rigid, like the waterfall model. 
Little flexibility and adjusting scope is difficult and
expensive. 
Software is developed during the implementation phase, so no
early prototypes of the software are produced. 
•	Model doesn’t provide a clear path for problems found
during testing phases