Cause No. 0	Cause No. 1	Cause No. 16	Cause No. 17	Cause No. 18
Cause No. 21	Cause No. 34	Cause No. 41	Cause No. 42	Cause No. 50
Cause No. 65	Cause No. 88	Cause No. 96	Cause No. 100	Cause No. 102

Common ISDN Event Cause Codes

A cause code alerts you that something is wrong with your ISDN connection. This Technote will give you the plain English version of what the cause code that is described means and how to resolve it.

NOTE: This technote describes some of the more frequently seen cause codes, but by no means the entire list. It attempts to relate the cause code and the problem it represents to real life experience. If you see a cause code that is not listed here, please refer to NIR_041: ISDN Event Cause Codes---Bellcore Standard. If you need further assistance after referring to this technote and that list of cause codes, please consult your local telephone company/ISDN line provider.

Cause No. 0

This is usually given by the router when none of the other codes apply. This cause usually occurs in the same type of situations as cause 1, cause 88, and cause 100.

Cause No. 1: 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).

What it Usually Means:

1. The SPIDS may be incorrectly entered in the Netopia or the Telco switch, giving a SPID failure in the WAN Event History.
2. The ISDN phone number being dialed by the router is invalid and the telco switch cannot locate the number to complete the call, as it is invalid.
3. On long distance calls, the call cannot be properly routed to its destination.

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.

What it Means:

This could be almost anything; it is the vaguest of the cause codes. The call comes down normally, but the reasons for it could be:

1. Lack of protocol negotiation, possibly due to misconfiguration of TCP/IP parameters on the router.
2. Link Timeouts of the call due to same.
3. Idle Timer at either end of the connection is activated.
4. A thousand other things.

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.

What It Means:

Calling end is Busy; no tricks here.

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).

What It Means:

The equipment on the other end does not answer the call. Usually this is a misconfiguration on the equipment being called.

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.

What It Means:

This is usually a telco issue. The call never reaches the final destination. This can be caused by bad switch translation from the Central office to the call's destination, or a misconfiguration on the equipment being called (i.e. not configured properly to answer calls).

Cause No. 34: no circuit/channel available.

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

What It Means:

There is no place on the Public Telephone network to place the call. Usually a temporary problem. The call never gets to its destination.

Cause No. 41: 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.

What It Means:

This means that there is a temporary failure at the physical layer on the ISDN network. If you remove the ISDN cable from the Netopia, you would see this. It's usually temporary.

Cause No. 42: switching equipment congestion.

This cause indicates that the switching equipment generating this cause is experiencing a period of high traffic.

What It Means:

Just too much going on at this point on the ISDN network to get the call through to its destination.

Cause No. 50: requested facility not subscribed.

This cause indicates that the requested supplementary service could not be provided by the network because the user has not completed the necessary administrative arrangements with its supporting networks.

What It Means:

The switch looks at the number being dialed and thinks it is for another service rather than ISDN. If the phone number is put in the correct format, the call should be placed properly. There are no standards for this, all Telcos have their own system for programming the number formats that the switches will recognize. Some systems want to see 7 digits, some 10, and others 11.

Cause No. 65: bearer capability not implemented.

This cause indicates that the equipment sending this cause does not support the bearer capability requested.

What It Means:

1. In most cases, the number being called is not an ISDN number but an analog destination.
2. The equipment is dialing at a faster rate than the circuitry allows, for example, dialing at 64K when only 56K is supported.

Cause No. 88: incompatible destination.

This cause indicates that the equipment sending this cause has received a request to establish a call that has a low layer compatibility, high layer compatibility, or other compatibility attributes (e.g., data rate) that cannot be accommodated.

What It Means:

1. This usually means that the Number To Dial in the Connection Profile is in the wrong format. You may need to dial a 10 or 11 digit number, or dial a 9 in front of the number if it is a Centrex line.
2. This problem may also give a Cause 111.
3. Dialing at the wrong line speed can also give this Cause.

Cause No. 96: mandatory information element is missing.

This cause indicates that the equipment sending this cause has received a message which is missing an information element which must be present in the message before that message can be processed.

What It Means:

This is rarely seen in North America but usually means that the number that is being dialed is in the wrong format, (similar to cause 88). Some part of the format being used is not understood by either the remote side equipment or the switching equipment between the source and destination of the call.

Cause No. 100: invalid information element contents.

This cause indicates that the equipment sending this cause has received and 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.

What It Means:

Like cause 1 and cause 88, this usually indicates that the ISDN number being dialed is in a format that is not understood by the equipment processing the call. SPIDs will sometimes fail to initialize with a Cause 100, or a call will fail with this cause.

Cause No. 102: recovery on timer expiry.

This cause indicates that a procedure has been initiated by the expiry of a timer in association with Q.931 handling procedures.

What it Means:

This is seen in situations where ACO (Alternate Call Offering) is being used. With this type of call pre-emption, the Telco switch operates a timer. For example, when an analog call is placed to a Netopia router that has two B Data Channels in place, the router relinquishes the second channel, but if it doesn't happen in the time allotted by the switch programming, the call will not ring through and will be discarded by the switch.