Teconologia

ISDN Cause Codes
Including current information from: • • • North American ISDN Users' Forum ITU Standards activity ANSI

ISDN Cause Codes
Fourth edition, published February, 22, 2003 by:

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This information has been compiled from many sources by AHK & Associates. Care has been taken to ensure the accuracy of this information, but no guarantee or warranty is implied or offered as to accuracy or usefulness. User assumes any and all risk or liability in using this information.

Introduction
Several things can go wrong during the ISDNcall setup. When they do the network will signal the nature of the fault via a code. When de-coded, the reason it occurred can be determined. Here are several examples of faults that can be reported. • • A setup request for a specific B-Channel when that channel is in use will cause the network to send a set release complete message with cause code # 44 “Requested circuit/channel unavailable”. Asetup request for a B channel when all B-Channels are in use will receive a release complete message from the network with cause code # 34 “No circuit/channel available”.

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The network might ignore a setup message with elements out of sequence. Procedures for this event are undecided. If the element is a vital one (e.g., called party number) the network could respond with setupacknowledge in place of call proceeding, and wait for additional information. A setup message with duplicated elements (ones that are not allowed to be duplicated) would get no indication from the network as it would simply act upon the first of the duplicated elements and ignore the rest. A setup message with missing mandatory elements will receive a status message from the network with causecode # 96 “Mandatory information element is missing”. A setup message with invalid content in any element will receive a release complete from the network with cause code # 100 “Invalid information element contents”. A setup message with unrecognized elements might receive nothing from the network as this area is still undecided. There is a trend for the network to send a status message with causecode # 99 “Information element non-existent or not implemented”.

Cause No. 1 - Unallocated (unassigned) number [Q.850]This cause indicates that the called party cannot be reached because, although the called party number is in a valid format, it is not currently allocated (assigned). Cause No. 2 - No route to specified transit network (national use) [Q.850] This cause indicates that theequipment sending this cause has received a request to route the call through a particular transit network, which it does not recognize. The equipment sending this cause does not recognize the transit network either because the transit network does not exist or because that particular transit network, while it does exist, does not serve the equipment which is sending this cause. Cause No. 3 - No route todestination [Q.850]

This cause indicates that the called party cannot be reached because the network through which the call has been routed does not serve the destination desired. This cause is supported on a network dependent basis.
Cause No. 4 - send special information tone [Q.850] This cause indicates that the called party cannot be reached for reasons that are of a long term nature andthat the special information tone should be returned to the calling party. Cause No. 5 - misdialed trunk prefix (national use) [Q.850] This cause indicates the erroneous inclusion of a trunk prefix in the called party number. This number is to stripped from the dialed number being sent to the network by the customer premises equipment. Cause No. 6 - channel unacceptable [Q.850] This cause...