QAS Approval Process

I want to understand, whether SOD (segregation of duties) is practiced in quality approval process. whether the person, who created a change request can approve the change request in QAS system?

what are the various role & responsibilities implemented in SAP change management process? what extent SOD (segregation of duties) is implemented in the same process?

Your answer will help me implement, some internal controls in our organization. We are one of the fortune 500 company (just to understand the size of the company)

Thanks in advance,

Krishna