ISDN, DDS/ADN, and T1 Events D-5This cause is not necessarily generated by Q.931 procedures butmay be generated by internal network timers.Cause No. 21: call rejected. This cause indicates that theequipment sending this cause does not wish to accept this call,although it could have accepted the call because the equipmentsending this cause is neither busy nor incompatible.Cause No. 22: number changed. This cause is returned to a callinguser when the called party number indicated by the calling user isno longer assigned. The new called party number may optionally beincluded in the diagnostic field. If a network does not support thiscapability, cause No. 1, unassigned (unallocated) number, shall beused.Cause No. 26: non-selected user clearing. This cause indicatesthat the specified user has not been awarded the incoming call.Cause No. 27: destination out of order. This cause indicates thatthe destination indicated by the user cannot be reached becausethe interface to the destination is not functioning correctly. The term“not functioning correctly” indicates that a signaling message wasunable to be delivered to the remote user: e.g., a physical layer ordata link layer failure at the remote user, user equipment off-line,etc.Cause No. 28: invalid number format (address incomplete). Thiscause indicates that the called user cannot be reached because thecalled party number is not a valid format or is not complete.Cause No. 29: facility rejected. This cause is returned when afacility requested by the user cannot be provided by the network.Cause No. 30: response to STATUS INQUIRY. This cause isincluded in the STATUS message when the reason for generated theSTATUS message was the prior receive of a STATUS INQUIRYmessage.Cause No. 31: normal, unspecified. This cause is used to report anormal even only when no other cause in the normal class applies.Cause No. 34: no circuit/channel available. This cause indicatesthat there is no appropriate circuit/channel presently available tohandle the call.
