A process may suspend itself or another process may suspend it.
A process to be suspended should be in the ready or current state.
Suspended processes go into the suspended state.
A process can be resumed only if it is in the suspended state.
A resumed process goes to the ready state (why not to the current state?)
The resume call returns the priority of the suspended process at the time that resume was called.
The suspend call returns the priority of the suspended process just before suspend terminates.
The reasons for returning priorities are obscure, but the fact that the priority of a process can change during a system call is interesting.
Look at transition diagram in figure 5.1 in the text book.