Understand cause codes: Q.850 and SIP

What it is for

Every finished call carries two cause values in the CDRs of the CUCM: one for the calling side and one for the called side. They state why the respective side ended the call. The values follow ITU recommendation Q.850 and are numbers from 1 to 127. EasyUC translates them into plain text in call analysis and in the itemized bill.

For SIP calls the CUCM additionally packs the SIP response code into the same numeric value. EasyUC splits this value and shows the Q.850 cause, the SIP status and always the raw value. In addition there are three Cisco special values for conference and transfer. Unknown values remain visible as "Code n".

The remedy given in this chapter describes the usual procedure. Which cause a provider or a gateway reports in a particular case depends on its configuration.

Prerequisites

Cause values exist only for calls with a CDR. The CDR import of the CUCM connection must be enabled.
For calls without a CDR, call analysis shows the last SIP status and, if present, the Q.850 cause from the SIP header Reason.
Role ROLE_APP_CALL_DIAGNOSTICS for call analysis.

Step by step: how to proceed

Open the call in call analysis and, on the Overview tab under Causes, read the rows Calling side and Called side.
Determine the side that counts. EasyUC uses the cause of the called side if it is not 0, otherwise that of the calling side.
Under Ended by, read which side hung up.
Look up the Q.850 cause in the following tables.
If the text also names a SIP status, look it up in the table of SIP responses and find it on the Call flow tab as a red arrow.
Check which lane the response comes from. That is the place where you continue looking.

Fields and options: how EasyUC derives cause and result

Fields and options: how EasyUC derives cause and result
Field / action	Meaning and use
Value 1 to 127	Plain Q.850 cause.
Large numeric value	Packed form: the top byte stands for the SIP status, the lowest byte for the Q.850 cause. Example: `1459617833` means SIP 503 and Q.850 41.
262144, 393216, 458752	Cisco special values: Conference full, Call split (transfer or conference), Conference participant dropped.
Result Answered	A CDR row has a connect time. The cause then describes the end of the conversation.
Result Busy	Q.850 17. Without a CDR: SIP 486 or 600.
Result No answer	Q.850 18 or 19. Without a CDR: SIP 408 or 480.
Result Rejected	Q.850 21, and also 16 or 31 on the called side. Without a CDR: SIP 403 or 603.
Result Unreachable	Q.850 1, 2, 3, 20, 22, 27 or 28. Without a CDR: SIP 404, 410, 484, 485 or 604.
Result Abandoned by caller	Q.850 16 or 31 on the calling side without a connection. Without a CDR: SIP 487 or a `CANCEL`.
Result Failed	Any other cause without a connection. Without a CDR: any other status from 300.
Result In progress / Unknown	From SIP only: no final response yet. Unknown if neither a cause nor a status is available.

Q.850: normal clearing and subscriber

Q.850: normal clearing and subscriber
Field / action	Meaning and use
16 Normal call clearing	One side hung up. Without a connection on the calling side: the caller hung up before the call was answered. No remedy needed.
31 Normal, unspecified	Ended without a more specific reason. Read it like 16. If it accumulates on one trunk, check that trunk's cause mapping.
17 User busy	The destination is already in a call, or the busy trigger of the line is reached. Check busy trigger, call waiting and call forward busy.
18 No user responding	The destination did not react to the call setup. Check the registration of the device and the network path.
19 No answer	The destination rang and nobody picked up. Check call forward no answer and its timer.
20 Subscriber absent	The destination is not signed in, for example a softphone that is not running. Check the registration status.
21 Call rejected	The destination or a rule actively declined the call. Check the block list, the CURRI rules and "Decline" on the phone.
26 Non-selected user clearing	On a shared line another device picked up. Normal.
126 Call split	Cisco value for transfer or conference. The call continues in another leg. Normal.

Q.850: number and route

Q.850: number and route
Field / action	Meaning and use
1 Unallocated number	The dialled number does not exist. Check the numbering plan, the partition and the calling search space of the caller.
2 No route to transit network	The provider does not know the route to the dialled network. Check the number format on the trunk and contact the provider.
3 No route to destination	No routing pattern matches, or the provider cannot reach the destination. Check route pattern and route list.
22 Number changed	The subscriber has a new number. Correct the destination number.
25 Exchange routing error	Error in the exchange of the far end, often a loop. Check the forwardings on both sides.
27 Destination out of order	The destination device or the line is faulty or not registered. Check registration, gateway port and line.
28 Invalid number format	The number is incomplete or wrongly formatted. Check the transformation patterns and prefixes on the trunk.
88 Incompatible destination	The destination does not support the requested type of connection, such as fax or video. Check device profile and region.
91 Invalid transit network selection	The network selection in the request is invalid. Clarify with the provider.

Q.850: network and resources

Q.850: network and resources
Field / action	Meaning and use
34 No circuit available	All channels of the trunk or gateway are in use. Check the number of channels, the concurrent calls and call admission control.
38 Network out of order	The far end reports a fault in the network. Check the status of the trunk and contact the provider.
41 Temporary failure	Short-lived error. Together with SIP 503 usually an unreachable trunk or a destination that does not respond. Check the reachability of the trunk and the OPTIONS ping.
42 Switching equipment congestion	The far end is overloaded. Try again later. If it accumulates, contact the provider.
43 Access information discarded	Additional information in the request was not passed on. Usually without consequences.
44 Requested channel not available	The requested channel is in use. Check the channel usage on the gateway.
47 Resource unavailable	A required resource is missing, in the CUCM often a transcoder, an MTP or the bandwidth of the location. Check the media resource group and the regions.
57 Bearer capability not authorized	The type of connection is not enabled for the line. Clarify with the provider.
58 Bearer capability not presently available	The type of connection is not possible at the moment. Check codec and region.
63 Service not available	The requested service is not available. Check the configuration of the destination.
65 Bearer capability not implemented	The far end does not support the type of connection, for example a codec. Check the codec selection of the region.
79 Service or option not implemented	A requested feature is missing at the far end. Switch off the feature or clarify with the provider.

Q.850: protocol and interworking

Q.850: protocol and interworking
Field / action	Meaning and use
29 Facility rejected / 50 Requested facility not subscribed / 69 Requested facility not implemented	The far end does not carry out a supplementary service. Clarify with the provider whether the service is subscribed.
81 Invalid call reference	The far end no longer knows the call. Usually the consequence of an earlier error. Read the flow before it in the call flow.
95 Invalid message / 96 Mandatory information element missing	A signalling message was faulty or incomplete. Open the affected message in the call flow and check the software version of the peer.
97, 98, 99, 100, 101	Message type or information element not implemented, invalid or not compatible with the call state. Proceed as for 95.
102 Recovery on timer expiry	A protocol timer expired because a response did not arrive. Find the long pause in the call flow and check the network path to that peer.
111 Protocol error	General protocol error. Open the error response in the call flow and read its text.
127 Interworking, unspecified	The cause comes from another network and could not be mapped more precisely. Continue looking at the gateway or CUBE; the original cause is there.
6, 7, 30, 70, 87	Channel unacceptable, Call awarded in established channel, Response to STATUS ENQUIRY, Only restricted digital bearer capability available, User not member of CUG. Rare, mostly on ISDN gateways.

SIP responses

SIP responses
Field / action	Meaning and use
401 Unauthorized / 407 Proxy Authentication Required	Request to authenticate. If a second `INVITE` with credentials follows, this is normal. If the error remains, the credentials of the device or trunk are wrong.
403 Forbidden	The peer refuses: not authorised, blocked or sender not permitted. Check the calling number and the permission on the trunk.
404 Not Found	Number unknown. If the response comes from the CUCM, check the numbering plan, otherwise the number format towards the trunk.
408 Request Timeout	No response within the expected time. Check the reachability of the peer.
480 Temporarily Unavailable	Destination not registered, not reachable or does not pick up.
481 Call/Transaction Does Not Exist	The peer no longer knows the dialog, often after a restart or a timeout.
484 Address Incomplete	The number is too short. Check the dial plan and the interdigit timeout.
486 Busy Here / 600 Busy Everywhere	Busy.
487 Request Terminated	Response to a `CANCEL`. The caller hung up, or a forwarding ended the first attempt.
488 Not Acceptable Here / 606 Not Acceptable	No common codec or unacceptable media parameters. Compare the SDP of both sides and check region and transcoder.
500 Server Internal Error	Internal error of the peer. Check its log.
502 Bad Gateway / 504 Server Time-out	A downstream system responds wrongly or not at all. Continue looking at the gateway or CUBE.
503 Service Unavailable	Service not available: trunk out of service, all channels in use or overload. Check the status of the trunk.
603 Decline	The called party declined.
604 Does Not Exist Anywhere	The number does not exist anywhere.

Check the result and narrow down errors

A finding is conclusive when result, Q.850 cause and the last response code in the call flow tell the same story, for example Busy, cause 17 and 486 Busy Here.
Calling side 0, called side set: the called side ended the call. In the opposite case the caller hung up.
Cause 16 on a call without a connection is not a system error. The caller did not wait long enough. The Ring time in the overview shows how long.
If only "Code n" is shown, the catalogue does not know the value. The raw value is next to it. Find the corresponding response code in the call flow.
For packed values, only the mapping for SIP 503 has been confirmed on a real CUCM. The other mappings follow the Cisco documentation. If in doubt, compare with the call flow.
Causes from the provider network arrive as the provider reports them. One and the same error can appear as 31, 41 or 127 depending on the provider.