This read-only up/down/testing/unknown/dormant INTEGER reports the interface's actual current operational state, which must read down(2) whenever ctDs0ifAdminStatus is down(2), and which becomes up(1) if the interface is ready to pass traffic or dormant(5) if it is waiting on some external action once admin status is set to up(1). An admin polls this to verify a DS0 channel that was administratively brought up has actually become ready to carry traffic. For example, an interface stuck reporting dormant(5) after being administratively enabled would tell the admin the channel is waiting on some external condition, such as far-end signaling, before it can pass traffic.