# SIP Response Codes and Call Disposition Reference Guide

## Introduction

The following table lists common SIP response codes, call dispositions, and Q.850 cause codes used in telephony systems. 
Use this reference to quickly understand call outcomes and troubleshoot call failures.


| Status Code | Disposition           | Cause                                              | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| ----------- | --------------------- | -------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| 0           | UNSPECIFIED           | Unspecified. No other cause codes applicable.      | 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.                                                                                                                                                                                                                                                                                         |
| 403         | Forbidden             | Outgoing calls barred                              | 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.                                                                                                                                                                                                                                                                                             |
| 404         | Not Found             | Unallocated (unassigned) number [Q.850 value 1]    | 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).                                                                                                                                                                                                                                                                                        |
| 484         | Address Incomplete    | 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.                                                                                                                                                                                                                                                                                                                     |
| 486         | Busy Here             | 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.                                                                                                                                |
| 487         | Request Terminated    | Caller disconnected before answer                  | This indicates that the person who made the incoming call dropped it before the call was answered.                                                                                                                                                                                                                                                                                                                                                            |
| 500         | Server Internal Error | 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.                                                                                                                                                                                                                                                |
| 502         | Bad Gateway           | Destination out of order                           | 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 offline.                                                                               |
| 603         | Decline               | 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. The network may also generate this cause, 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. |