The definitive SIP/ISDN cause and response code list

Interworking between circuit switched and packet switched telecommunications can be problematic when crossing network boundaries.  This is especially true with origination or termination of calls between ISDN and SIP networks.  Below is the definitive list of typical ISDN/SS7 user part cause codes along with SIP response codes.

ISDN-to-SIP translations

wdt_IDISUP Cause CodeISUP DescriptionSIP ResponseSIP Description
11Unallocated (assigned) number404Not found
22No route to network404Not found
33No route to destination404Not found
416Normal call clearingBYE/CANCEL
517User Busy486Busy here
618No user responding408Request timeout
719No answer from the user480Temporarily unavailable
820Subscriber absent480Temporarily unavailable
921Call rejected403Forbidden
1022Number changed (s/ o diagnostic)410Gone
ISUP Cause CodeISUP DescriptionSIP ResponseSIP Description

SS7 ISUP (ISDN User Part) cause code list:

Cause Code l – Unallocated (unassigned) number [Q.850]
This cause indicates that the called party cannot be reached recluses although the called party number is in a valid format. It is not currently allocated (assigned).

Cause Code 2 – No route to specified transit network (national use) [Q.850]
This cause indicates that the equipment 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 Code 3 – No route to destination [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 Code 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 and that the special information tone should be returned to the calling party.

Cause Code 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 sniped from the dialed number being sent to the network by the customer premises equipment.

Cause Code 6 – channel unacceptable [Q.850]
This cause indicates that the channel most recently identified is not acceptable to the sending entity for use in this call.

Cause Code 7 – call awarded. being delivered in an established channel [Q.850]
This cause indicates that the user has been awarded the incoming call and that the incoming call is being connected to a channel already established to that user for similar calls (e.g. packet-mode x.25 virtual calls).

Cause Code 8 – preemption [Q.850]
This cause indicates the call is being preempted.

Cause Code 9 – preemption – circuit reserved for reuse [Q.850]
This cause indicates that the call is being preempted and the circuit is reserved for reuse by the preempting exchange.

Cause Code 10 – normal call clearing [Q.850]
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. Under normal situations, the source of this cause is not the network.

Cause Code 17 – user busy [Q.850]
This cause is used to indicate that the called party is unable to accept another call because the user busy condition has been encountered. This cause value may be generated by the called user or by the network. In the case of user determined user busy it is noted that the user equipment is compatible with the call.

Cause Code 18 – no user responding [Q.850]
This cause is used when a called party does not respond to a call establishment message with either an alerting or connect indication within the prescribed period of time allocated.

Cause Code 19 – no answer from user (user alerted) [Q.850]
This cause is used when the called party has been alerted but does not respond with a connect indication within a prescribed period of time. Note – This cause is not necessarily generated by Q.931 procedures but may be generated by internal network timers.

Cause Code 20 – subscriber absent [Q.850]
This cause value is used when a mobile station has logged off. radio contact is not obtained with a mobile station or if a personal telecommunication user is temporarily not addressable at any user-network interface.

Cause Code 21 – call rejected [Q.850]
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. This cause may also be generated by the network, indicating that the call was cleared due to a supplementary service constraint. The diagnostic field may contain additional information about the supplementary service and reason for rejection.

Cause Code 22 – number changed [Q.850]
This cause is returned to a calling party when the called party number indicated by the calling party is no longer assigned. The new called party number may optionally be included in the diagnostic field. If a network does not support this cause, cause no. 1, unallocated (unassigned) number shall be used.

Cause Code 26 – non-selected user clearing [Q.850]
This cause indicates that the user has not been awarded the incoming call.

Cause Code 27 – destination out of order [Q.850]
This cause indicates that the destination indicated by the user cannot be reached because the interface to the destination is not functioning correctly. The term “not functioning correctly” indicates that a signal message was unable to be delivered to the remote party; e.g., a physical layer or data link layer failure at the remote party or user equipment off-line.

Cause Code 28 – invalid number format (address incomplete) [Q.850]
This cause indicates that the called party cannot be reached because the called party number is not in a valid format or is not complete.

Cause Code 29 – facilities rejected [Q.850]
This cause is returned when a supplementary service requested by the user cannot be provide by the network.

Cause Code 30 – response to STATUS INQUIRY [Q.850]
This cause is included in the STATUS message when the reason for generating the STATUS message was the prior receipt of a STATUS INQUIRY.

Cause Code 31 – normal. unspecified [Q.850]
This cause is used to report a normal event only when no other cause in the normal class applies.

Cause Code 34 – no circuit/channel available [Q.850]
This cause indicates that there is no appropriate circuit/channel presently available to handle the call.

Cause Code 35 – Call Queued [Q.850]

Cause Code 38 – network out of order [Q.850]
This cause indicates that the network is not functioning correctly and that the condition is likely to last a relatively long period of time e.g., immediately re-attempting the call is not likely to be successful.

Cause Code 39 – permanent frame mode connection out-of-service [Q.850]
This cause is included in a STATUS message to indicate that a permanently established frame mode connection is out-of-service (e.g. due to equipment or section failure) (see Annex A/Q.933)

Cause Code 40 – permanent frame mode connection operational [Q.850]
This cause is included in a STATUS message to indicate that a permanently established frame mode connection is operational and capable of carrying user information. (see Annex A/Q.933]

Cause Code 41 – temporary failure [Q.850]
This cause indicates that the network is not functioning correctly and that the condition is no likely to last a long period of time; e.g., the user may wish to try another call attempt almost immediately.

Cause Code 42 – switching equipment congestion [Q.850]
This cause indicates that the switching equipment generating this cause is experiencing a period of high traffic.

Cause Code 43 – access information discarded [Q.850]
This cause indicates that the network could not deliver access information to the remote user as requested. i.e., user-to-user information, low layer compatibility, high layer compatibility or sub-address as indicated in the diagnostic. It is noted that the particular type of access information discarded is optionally included in the diagnostic.

Cause Code 44 – requested circuit/channel not available [Q.850]
This cause is returned when the circuit or channel indicated by the requesting entity cannot be provided by the other side of the interface.

Cause Code 46 – precedence call blocked [Q.850]
This cause indicates that there are no predictable circuits or that the called user is busy with a call of equal or higher preventable level.

Cause Code 47 – resource unavailable, unspecified [Q.850]
This cause is used to report a resource unavailable event only when no other cause in the resource unavailable class applies.

Cause Code 49 – Quality of Service not available [Q.850]
This cause is used to report that the requested Quality of Service. as defined in Recommendation X.213. cannot be provided (e.g., throughput of transit delay cannot be supported).

Cause Code 50 – requested facility not subscribed [Q.850]

This cause indicates that the user has requested a supplementary service which is implemented by the equipment which generated this cause but the user is not authorized to use.

Cause Code 52 – outgoing calls barred

Cause Code 53 – outgoing calls barred within CUG [Q.850]
This cause indicates that although the calling party is a member of the CUG for the outgoing CUG call. Outgoing calls are not allowed for this member of the CUG.

Cause Code 54 – incoming calls barred

Cause Code 55 – incoming calls barred within CUG [Q.850]
This cause indicates that although the calling party is a member of the CUG for the incoming CUG call. Incoming calls are not allowed for this member of the CUG.

Cause Code 57 – bearer capability not authorized [Q.850]
This cause indicates that the user has requested a bearer capability which is implemented by the equipment which generated this cause but the user is not authorized to use.

Cause Code 58 – bearer capability not presently available [Q.850]
This cause indicates that the user has requested a bearer capability which is implemented by the equipment which generated this cause but which is not available at this time.

Cause Code 62 – inconsistency in outgoing information element. [Q.850]
This cause indicates an inconsistency in the designated outgoing access information and subscriber class

Cause Code 63 – service or option not available. unspecified [Q.850]
This cause is used to report a service or option not available event only when no other cause in the service or option not available class applies.

Cause Code 65 – bearer capability not implemented [Q.850]
This cause indicates that the equipment sending this cause does not support the bearer capability requested.

Cause Code 66 – channel type not implemented [Q.850]
This cause indicates that the equipment sending this cause does not support the channel type requested

Cause Code 69 – requested facility not implemented [Q.850]
This cause indicates that the equipment sending this cause does not support the requested supplementary services.

Cause Code 70 – only restricted digital information bearer capability is available (national use) [Q.850]
This cause indicates that the calling party has requested an unrestricted bearer service but the equipment sending this cause only supports the restricted version of the requested bearer capability.

Cause Code 79 – service or option not implemented unspecified [Q.850]
This cause is used to report a service or option not implemented event only when no other cause in the service or option not implemented class applies.

Cause Code 81 – invalid call reference value [Q.850]
This cause indicates that the equipment sending this cause has received a message with a call reference which is not currently in use on the user-network interface.

Cause Code 82 – identified channel does not exist [Q.850]
This cause indicates that the equipment sending this cause has received a request to use a channel not activated on the interface for a call. For example. if a user has subscribed to those channels on a primary rate interface numbered from l to 12 and the user equipment or the network attempts to use channels l 3 through 23, this cause is generated.

Cause Code 83 – a suspended call exists, but this call identify does not [Q.850]
This cause indicates that a call resume has been attempted with a call identity which differs from that in use for any presently suspended call(s).

Cause Code 84 – call identity in use [Q.850]
This cause indicates that the network has received a call suspended request containing a call identity (including the null call identity) which is already in use for a suspended call within the domain of interfaces over which the call might be resumed.

Cause Code 85 – no call suspended [Q.850]
This cause indicates that the network has received a call resume request containing a Call identity information element which presently does not indicate any suspended call within the domain of interfaces over which calls may be resumed.

Cause Code 86 – call having the requested call identity has been cleared [Q.850]
This cause indicates that the network has received a call resume request containing a Call identity information element indicating a suspended call that has in the meantime been cleared while suspended (either by network time-out or by the remote user).

Cause Code 87 – user not a member of CUG [Q.850]
This cause indicates that the called user for the incoming CUG call is not a member of the specified CUG or that the calling user is an ordinary subscriber calling a CUG subscriber.

Cause Code 88 – incompatible destination [Q.850]
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.

Cause Code 90 – non-existent CUG [Q.850]
This cause indicates that the specified CUG does not exist.

Cause Code 91 – invalid transit network selection (national use) [Q.850]
This cause indicates that a transit network identification was received which is of an incorrect format as defined in Annex C/Q.931

Cause Code 95 – invalid message, unspecified [Q.850]
This cause is used to report an invalid message event only when no other cause in the invalid message class applies.

Cause Code 96 – mandatory information element is missing [Q.850]
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.

Cause Code 97 – message type non-existent or not implemented [Q.850]
This cause indicates that the equipment sending this cause has received a message with a message type it does not recognize either because this is a message not defined of defined but not implemented by the equipment sending this cause.

Cause Code 98 – message not compatible with call state or message type non-existent or not implemented. [Q.850]
This cause indicates that the equipment sending this cause has received a message such that the procedures do not indicate that this is a permissible message to receive while in the call state. or a STATUS message was received indicating an incompatible call state.

Cause Code 99 – Information element / parameter non-existent or not implemented [Q.850]
This cause indicates that the equipment sending this cause has received a message which includes information element(s)/parameter(s) not recognized because the information element(s)/parameter name(s) are not defined or are defined but not implemented by the equipment sending the cause. This cause indicates that the information element(s)/parameter(s) were discarded. However, the information element is not required to be present in the message in order for the equipment sending the cause to process the message.

Cause Code 100 – Invalid information element contents [Q.850]
This cause indicates that the equipment sending this cause has received and information element which it has implemented; however, one or more Gelds in the I.E. are coded in such a way which has not been implemented by the equipment sending this cause.

Cause Code 101 – message not compatible with call state [Q.850]
This cause indicates that a message has been received which is incompatible with the call state.

Cause Code 102 – recovery on timer expiry [Q.850]
This cause indicates that a procedure has been initiated by the expiration of a timer in association with error handling procedures.

Cause Code 103 – parameter non-existent or not implemented – passed on (national use) [Q.850]
This cause indicates that the equipment sending this cause has received a message which includes parameters not recognized because the parameters are not defined or are defined but not implemented by the equipment sending this cause. The cause indicates that the parameter(s) were ignored. In addition, if the equipment sending this cause is an intermediate point, then this cause indicates that the parameter(s) were passed unchanged.

Cause Code 110 – message with unrecognized parameter discarded [Q.850]
This cause indicates that the equipment sending this cause has discarded a received message which includes a parameter that is not recognized.

Cause Code 111 – protocol error, unspecified [Q.850]
This cause is used to report a protocol error event only when no other cause in the protocol error class applies.

Cause Code 127 – Intel-working, unspecified [Q.850]
This cause indicates that an interworking call (usually a call to 5W56 service) has ended.

SIP Response codes list:

SIP 100 – Trying
Extended search being performed may take a significant time so a forking proxy must send a 100 Trying response.

SIP 180 – Ringing
Destination user agent received INVITE, and is alerting user of call.

SIP 181 – Call is Being Forwarded
Servers can optionally send this response to indicate a call is being forwarded.

SIP 182 – Queued
Indicates that the destination was temporarily unavailable, so the server has queued the call until the destination is available. A server may send multiple 182 responses to update progress of the queue.

SIP 183 – Session Progress
This response may be used to send extra information for a call which is still being set up.

SIP 199 – Early Dialog Terminated
Can be used by User Agent Server to indicate to upstream SIP entities (including the User Agent Client (UAC)) that an early dialog has been terminated.

SIP 200 – OK
Indicates the request was successful.

SIP 202 – Accepted
Indicates that the request has been accepted for processing, but the processing has not been completed. Deprecated.

SIP 204 – No Notification
Indicates the request was successful, but the corresponding response will not be received.

SIP 300 – Multiple Choices
The address resolved to one of several options for the user or client to choose between, which are listed in the message body or the message’s Contact fields.[1]:§21.3.1

SIP 301 – Moved Permanently
The original Request-URI is no longer valid, the new address is given in the Contact header field, and the client should update any records of the original Request-URI with the new value.

SIP 302 – Moved Temporarily
The client should try at the address in the Contact field. If an Expires field is present, the client may cache the result for that period of time.

SIP 305 – Use Proxy
The Contact field details a proxy that must be used to access the requested destination.

SIP 380 Alternative Service
The call failed, but alternatives are detailed in the message body.

SIP 400 – Bad Request
The request could not be understood due to malformed syntax.

SIP 401 – Unauthorized
The request requires user authentication. This response is issued by UASs and registrars.

SIP 402 – Payment Required
Reserved for future use.

SIP 403 – Forbidden
The server understood the request, but is refusing to fulfill it.[1]:§21.4.4 Sometimes (but not always) this means the call has been rejected by the receiver.

SIP 404 – Not Found
The server has definitive information that the user does not exist at the domain specified in the Request-URI. This status is also returned if the domain in the Request-URI does not match any of the domains handled by the recipient of the request.

SIP 405 – Method Not Allowed
The method specified in the Request-Line is understood, but not allowed for the address identified by the Request-URI.

SIP 406 – Not Acceptable
The resource identified by the request is only capable of generating response entities that have content characteristics but not acceptable according to the Accept header field sent in the request.

SIP 407 – Proxy Authentication Required
The request requires user authentication. This response is issued by proxys.

SIP 408 – Request Timeout
Couldn’t find the user in time. The server could not produce a response within a suitable amount of time, for example, if it could not determine the location of the user in time. The client MAY repeat the request without modifications at any later time.

SIP 409 – Conflict
User already registered. Deprecated by omission from later RFCs and by non-registration with the IANA.

SIP 410 – Gone
The user existed once, but is not available here any more.

SIP 411 – Length Required
The server will not accept the request without a valid Content-Length. Deprecated by omission from later RFCs and by non-registration with the IANA.

SIP 412 – Conditional Request Failed
The given precondition has not been met.

SIP 413 – Request Entity Too Large
Request body too large.

SIP 414 – Request-URI Too Long
The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret.

SIP 415 – Unsupported Media Type
Request body in a format not supported.

SIP 416 – Unsupported URI Scheme
Request-URI is unknown to the server.

SIP 417 – Unknown Resource-Priority
There was a resource-priority option tag, but no Resource-Priority header.

SIP 420 – Bad Extension
Bad SIP Protocol Extension used, not understood by the server.

SIP 421 – Extension Required
The server needs a specific extension not listed in the Supported header.

SIP 422 – Session Interval Too Small
The received request contains a Session-Expires header field with a duration below the minimum timer.

SIP 423 – Interval Too Brief
Expiration time of the resource is too short.

SIP 424 – Bad Location Information
The request’s location content was malformed or otherwise unsatisfactory.

SIP 428 – Use Identity Header
The server policy requires an Identity header, and one has not been provided.

SIP 429 – Provide Referrer Identity
The server did not receive a valid Referred-By token on the request.

SIP 430 – Flow Failed
A specific flow to a user agent has failed, although other flows may succeed. This response is intended for use between proxy devices, and should not be seen by an endpoint (and if it is seen by one, should be treated as a 400 Bad Request response).

SIP 433 – Anonymity Disallowed
The request has been rejected because it was anonymous.

SIP 436 – Bad Identity-Info
The request has an Identity-Info header, and the URI scheme in that header cannot be dereferenced.

SIP 437 – Unsupported Certificate
The server was unable to validate a certificate for the domain that signed the request.

SIP 438 – Invalid Identity Header
The server obtained a valid certificate that the request claimed was used to sign the request, but was unable to verify that signature.

SIP 439 – First Hop Lacks Outbound Support
The first outbound proxy the user is attempting to register through does not support the “outbound” feature of RFC 5626, although the registrar does.

SIP 440 – Max-Breadth Exceeded
If a SIP proxy determines a response context has insufficient Incoming Max-Breadth to carry out a desired parallel fork, and the proxy is unwilling/unable to compensate by forking serially or sending a redirect, that proxy MUST return a 440 response. A client receiving a 440 response can infer that its request did not reach all possible destinations.

SIP 469 – Bad Info Package
If a SIP UA receives an INFO request associated with an Info Package that the UA has not indicated willingness to receive, the UA MUST send a 469 response, which contains a Recv-Info header field with Info Packages for which the UA is willing to receive INFO requests.

SIP 470 – Consent Needed
The source of the request did not have the permission of the recipient to make such a request.

SIP 480 – Temporarily Unavailable
Callee currently unavailable.

SIP 481 – Call/Transaction Does Not Exist
Server received a request that does not match any dialog or transaction.

SIP 482 – Loop Detected
Server has detected a loop.

SIP 483 – Too Many Hops
Max-Forwards header has reached the value ‘0’.

SIP 484 – Address Incomplete
Request-URI incomplete.

SIP 485 – Ambiguous
Request-URI is ambiguous.

SIP 486 – Busy Here
Callee is busy.

SIP 487 – Request Terminated
Request has terminated by bye or cancel.

SIP 488 – Not Acceptable Here
Some aspect of the session description or the Request-URI is not acceptable, or Codec issue.

SIP 489 – Bad Event
The server did not understand an event package specified in an Event header field.

SIP 491 – Request Pending
Server has some pending request from the same dialog.

SIP 493 – Undecipherable
Request contains an encrypted MIME body, which recipient can not decrypt.

SIP 494 – Security Agreement Required
The server has received a request that requires a negotiated security mechanism, and the response contains a list of suitable security mechanisms for the requester to choose between, or a digest authentication challenge.

SIP 500 – Server Internal Error
The server could not fulfill the request due to some unexpected condition.

SIP 501 – Not Implemented
The server does not have the ability to fulfill the request, such as because it does not recognize the request method. (Compare with 405 Method Not Allowed, where the server recognizes the method but does not allow or support it.)

SIP 502 – Bad Gateway
The server is acting as a gateway or proxy, and received an invalid response from a downstream server while attempting to fulfill the request.

SIP 503 – Service Unavailable
The server is undergoing maintenance or is temporarily overloaded and so cannot process the request. A “Retry-After” header field may specify when the client may reattempt its request.

SIP 504 – Server Time-out
The server attempted to access another server in attempting to process the request, and did not receive a prompt response.

SIP 505 – Version Not Supported
The SIP protocol version in the request is not supported by the server.

SIP 513 – Message Too Large
The request message length is longer than the server can process.

SIP 580 – Precondition Failure
The server is unable or unwilling to meet some constraints specified in the offer.

SIP 600 – Busy Everywhere
All possible destinations are busy. Unlike the 486 response, this response indicates the destination knows there are no alternative destinations (such as a voicemail server) able to accept the call.

SIP 603 – Decline
The destination does not wish to participate in the call, or cannot do so, and additionally the destination knows there are no alternative destinations (such as a voicemail server) willing to accept the call.

SIP 604 – Does Not Exist Anywhere
The server has authoritative information that the requested user does not exist anywhere.

SIP 606 – Not Acceptable
The user’s agent was contacted successfully but some aspects of the session description such as the requested media, bandwidth, or addressing style were not acceptable.

SIP 607 – Unwanted
The called party did not want this call from the calling party. Future attempts from the calling party are likely to be similarly rejected.



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