This attribute specifies the maximum amount of time that the IWF
waits for an Originator Detection Pattern (ODP) or Answerer
Detection Pattern (ADP). ODP/ADP is a series of special bit
patterns used during the call setup procedures.
If the IWF is the Originator of the call, it starts sending ODP
patterns and waits for an ADP for the duration of T400 milliseconds
from the answerer at call setup time.
If the IWF is the Answerer of the call, it waits for an ODP for T400
seconds from the originator and if it receives during that time it
sends an ADP pattern to the originator at the call setup time. Since
both sides operate with different values of T400 timer, a higher
value increases the chance of a successful call setup.
Changes to this attribute do not effect existing calls.