This attribute specifies the maximum amount of time that the IWF
waits for an acknowledgment before retransmitting a frame. Since
information about the T401 timer is not carried in the Exchange
Identification (XID) negotiations at call setup time, both sides
operate with different timer values. The value for T401 depends on
many factors, such as propagation delay or frame processing time.
A frame is retransmitted up to N400 times if the timer T401 expires
before an acknowledgment for a frame is actually received. The
performance of the data link layer can be impacted by the value of
this timer as retransmissions of frames occur on expiry of timer
T401.
Changes to this attribute do not effect existing calls.