Netopia 435 Reference Manual page 247

E-4 Netopia ISDN Router Reference Guide
This cause is supported on a network-dependent basis.
Cause No. 6: channel unacceptable. This cause indicates that the
channel most recently identified is not acceptable to the sending
entity for use in this call.
Cause No.7: call awarded and being delivered in an established
channel. This cause indicates that the user has been awarded the
incoming call, and that the incoming call is being connected to a
channel already established to that user for similar calls (e.g.,
packet-mode X.25 virtual calls).
Cause No. 16: normal call clearing. This cause indicates that the
call is being cleared because one of the users involved in the call
has requested that the call be cleared.
Under normal situations, the source of this cause is not the
network.
Cause No. 17: user busy. This cause is used when the called user
has indicated the inability to accept another call.
It is noted that the user equipment is compatible with call.
Cause No. 18: no user responding. This cause is used when a
user does not respond to a call establishment message with either
an alerting or connect indication within the prescribed period of time
allocated (defined in Recommendation Q.931 by the expiry of either
timer T303 or T310).
Cause No. 19: no answer from user (user alerted). This cause is
used when a user has provided an alerting indication but has not
provided a connect indication within a prescribed period of time.
This cause is not necessarily generated by Q.931 procedures but
may be generated by internal network timers.
Cause No. 21: call rejected. This cause indicates that the
equipment sending this cause does not wish to accept this call,
although it could have accepted the call because the equipment
sending this cause is neither busy nor incompatible.