WATM — A possible race condition with location updates during recovery

When a terminal loses connection to its current Access Bridge, section
4.1 says that the Access Bridge deregisters the terminal by invoking
update_location at the Home Location Agent giving NIL as the new
Access Bridge reference. Assume now that the terminal is performing
an access recovery to a new Access Bridge. It may happen that the new
Access Bridge invokes update_location, then the old Access Bridge, not
yet knowing about the recovery in progress, deregisters the terminal
and only after that the new Access Bridge invokes recovery_request at
the old Access Bridge. This sequence of events leaves the Home
Location Agent to believe mistakenly that the terminal does not have
an associated Access Bridge.

A possible solution: Add a deregister() operation to the
HomeLocationAgent interface. This operation would take as parameters
the terminal id and the Access Bridge invoking it, and would return a
boolean value. The Home Location Agent could then compare whether the
invoking Access Bridge is the same as the Access Bridge it believes to
be current. If it is, the HLA deregisters the terminal and returns
true, otherwise the HLA does nothing and returns false. Now, from the
return value, the invoking Access Bridge can tell whether there is an
access recovery in progress, and if so, can prepare for it by hanging
on to the terminal's information.

see above