State Transition Table

Status	non-`normal`	user `ack`	new > old	new <= old	`normal`	timeout
`open`	`open`	`ack`			`closed`	`expired`
`ack`			`open`	`ack`	`closed`
`assign`
`closed`	`open`				`closed`
`expired`	`open`				`closed`