This description is taken directly from ECMA
269.
6.8.6 Tracking a Diverted Call
When observing a call or a device in a call, and the call diverts from
a device in the call, the computing function
shall use the Diverted event to track the progress of the call as a
result of the redirection.
If the switching function does not provide the Diverted event for all
devices in a call or for call-type monitors (as
indicated through the capabilities exchange services), the computing
function shall use parameters in the first event
after the call has been diverted to properly track the progress of
the call as a result of the redirection. The device
identifiers are used to observe the movement of the call and the event
cause is provided to indicate what caused the
movement of the call. (Note that the call may have been diverted several
times between the previous event (if one
was generated) and the first event after the diversion. As a result,
the computing function can only ascertain that
either one or two redirections have occurred.)