Difference Peer Lagged and Unreachable

With “Qualify=Yes”, and the peer not responding within the default 2000ms, is the peer then considered Lagged or Unreachable?
In fact, when is a peer considered Lagged and when Unreachable?

When you enable qualify in sip.conf (or its includes), you specify a time in ms. If the far end doesn’t respond within the qualify time specified, but does respond, the connection is considered lagged. If the far end never responds, it is unreachable. Setting qualify=yes is the functional equivalent of setting qualify=2000.