Typical ISDN Cause Codes

Normal Class 
Code Description 

001 Unallocated/unassigned number 
   This cause indicates that the destination requested by the calling user
cannot be reached because, although the number is in a valid format, it is
not currently assigned (allocated). 

016 Normal call clearing 
   This cause indicates that the call is being cleared because one of the
users involved has requested that the call be cleared. 
   Under normal situations, the source of this cause is not the network.
 
017 User busy 
   This cause is used when the called user has indicated the ability to
accept another call. 
   It is noted that the user equipment is compatible with the call. 

018 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. 

021 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. 

Resource Unavailable Class 
Code Description 

034 No circuit/channel available 
   This cause indicates that there is no appropriate circuit/channel
presently available to handle the call. 

041 Temporary failure 
   This cause indicates that the network is not functioning correctly and
that the condition is not likely to last a long period of time; e.g., the
user may wish to try another call attempt almost immediately. 
Service or Option Not Implemented Class 
Code Description 

088 Incompatible destination 
   This cause indicates that the equipment sending this cause has received a
request to establish a call which has low layer compatibility, high layer
compatibility, or other compatibility attributes (e.g., data rate) which
cannot be accommodated. 
Protocol Error (e.g., Unknown Message) Class 
Code Description 

100 Invalid information element contents 
   This cause indicates that the equipment sending this cause has received
an information element which it has implemented; however, one or more of the
fields in the information element are coded in such a way which has not been
implemented by the equipment sending this cause.