A XYZ technology is known for its research in distributed computing domain. It has recently entered the block chain market for delivering security services for financial sector. SS Tech is its oldest business client and has offered XYZ technologies to develop a block chain framework for its financial transactions. The functional testing phase was completed successfully but during the review meeting, SS Tech had a requirement change. As software analyst, which software process model would you suggest for this scenario and explain the different phases in that model.