SIP 480 and 486 and 603 responses

See also

Sources

1. 1
   Asterisk documents SIP 480 and 483 as corresponding to ISDN cause 19 No answer from user (AST_CAUSE_NO_ANSWER), and SIP 408 as cause 18 No user responding.

   Hangup Cause Mappings · Asterisk Hangup Cause Code Mappings table, rows 18 and 19 · Checked 2026-10-14
2. 2
   Asterisk's documented SIP-to-cause pairing of 480 with cause 19 appears to differ from RFC 3398, which maps an outgoing 480 to cause 18, so a 480 may surface as different ISDN causes on Asterisk and on an RFC 3398 gateway.inferred

   Hangup Cause Mappings · Asterisk Hangup Cause Code Mappings table, row 19; compare RFC 3398 Section 8.2.6.1 row 480 · Checked 2026-10-14
3. 3
   Asterisk documents SIP 486 and 600 as corresponding to ISDN cause 17 User busy (AST_CAUSE_USER_BUSY).

   Hangup Cause Mappings · Asterisk Hangup Cause Code Mappings table, row 17 User busy · Checked 2026-10-14
4. 4
   Asterisk documents SIP 603, together with 401, 403 and 407, as corresponding to ISDN cause 21 Call Rejected.

   Hangup Cause Mappings · Asterisk Hangup Cause Code Mappings table, row 21 Call Rejected · Checked 2026-10-14
5. 5
   Asterisk's Dial application sets DIALSTATUS to BUSY when the called party is busy or signals busy, and the documentation warns that some SIP devices return 486 when Do Not Disturb is active.

   Dial (Dialplan Application) · Dial > DIALSTATUS > BUSY · Checked 2026-10-14
6. 6
   Cisco says Unified CM lines have a busy trigger, and once active calls reach it Unified CM itself initiates Call Forward Busy without sending another INVITE to the phone.

   SIP Line Messaging Guide (Standard Edition) for Cisco Unified Communications Manager - SIP Standard Line Interface · SIP Standard Line Interface > Standard Feature Scenarios > Endpoint Returns 486 Busy · Checked 2026-10-14
7. 7
   Cisco says phones supporting x-Cisco-callinfo and extended REFER do not get a 486 when calling a busy line; Unified CM sends 183 Session Progress with Call-Info ui-state=busy and requests busy tone via REFER.

   SIP Line Messaging Guide (Standard Edition) for Cisco Unified Communications Manager - SIP Standard Line Interface · SIP Standard Line Interface > UI State (busy handling) · Checked 2026-10-14
8. 8
   Cisco says that when a SIP phone itself answers an INVITE with 486, Unified CM does not exercise the line's configured Call Forward Busy and passes the 486 back toward the caller.

   SIP Line Messaging Guide (Standard Edition) for Cisco Unified Communications Manager - SIP Standard Line Interface · SIP Standard Line Interface > Standard Feature Scenarios > Endpoint Returns 486 Busy · Checked 2026-10-14
9. 9
   Microsoft says that when Teams rejects an inbound Direct Routing call because the user is busy or declines it, the PSTN carrier or SBC might retry the call and Teams shows a separate missed-call notification for each retry.

   Issues that affect inbound Direct Routing calls · Section 'Multiple notifications about missed calls' · Checked 2026-10-14
10. 10
    Microsoft says Direct Routing follows NICC ND1017:2006/07 and maps SIP 486 to Q.850 cause 17.

    Issues that affect inbound Direct Routing calls · Section 'Multiple notifications about missed calls', third paragraph · Checked 2026-10-14
11. 11
    Microsoft says an SBC, network device or PSTN provider retrying a call after a SIP 4xx response that ends the call is not recommended, and asks for that retry behaviour to be disabled.

    Issues that affect inbound Direct Routing calls · Section 'Multiple notifications about missed calls', subsection Resolution, second paragraph · Checked 2026-10-14
12. 12
    Microsoft Learn states that RFC 4497 maps SIP 486 to Q.850 cause 34 and that this differs from the Direct Routing mapping.disputed

    Issues that affect inbound Direct Routing calls · Section 'Multiple notifications about missed calls', third paragraph · Checked 2026-10-14
13. 13
    Microsoft's fix for repeated retries after a Teams busy rejection is to change SBC SIP manipulation rules to remove the Q.850 cause mapped to 486 or change it from 34 to 17.

    Issues that affect inbound Direct Routing calls · Section 'Multiple notifications about missed calls', subsection Resolution, first paragraph · Checked 2026-10-14
14. 14
    Oracle Communications SBC 9.3.0 default Q.850-to-SIP mappings send cause 17 as 486, cause 18 as 408, causes 19, 20 and 31 as 480, and cause 21 as 603 when location is user or 403 otherwise, when no configured map entry matches.

    SIP Statuses to Q.850 Reasons · SIP Statuses to Q.850 Reasons > Default Mappings table · Checked 2026-10-14
15. 15
    RFC 3261 defines 480 Temporarily Unavailable as the callee's end system being contacted successfully while the callee is currently unavailable, giving not logged in, a state precluding communication, or an activated do-not-disturb feature as examples.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.4.18 480 Temporarily Unavailable · Checked 2026-10-14
16. 16
    RFC 3261 says 480 is also returned by a redirect or proxy server that recognizes the user in the Request-URI but does not currently have a valid forwarding location for that user.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.4.18 480 Temporarily Unavailable · Checked 2026-10-14
17. 17
    RFC 3261 says the reason phrase of a 480 response SHOULD indicate a more precise cause for why the callee is unavailable.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.4.18 480 Temporarily Unavailable · Checked 2026-10-14
18. 18
    RFC 3261 allows a 480 response to indicate a better time to call in a Retry-After header field.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.4.18 480 Temporarily Unavailable · Checked 2026-10-14
19. 19
    RFC 3261 notes that a user returning 486 could also be available elsewhere, such as through a voice mail service, because 486 is scoped to the end system that answered.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.4.24 486 Busy Here · Checked 2026-10-14
20. 20
    RFC 3261 defines 486 Busy Here as the callee's end system being contacted successfully while the callee is not willing or able to take additional calls at that end system.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.4.24 486 Busy Here · Checked 2026-10-14
21. 21
    RFC 3261 allows a 486 response to indicate a better time to call in a Retry-After header field.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.4.24 486 Busy Here · Checked 2026-10-14
22. 22
    RFC 3261 says 600 Busy Everywhere SHOULD be used instead of 486 if the client knows that no other end system will be able to accept the call.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.4.24 486 Busy Here · Checked 2026-10-14
23. 23
    RFC 3261 describes 4xx responses as definite failures from a particular server and says the same request to a different server might succeed.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.4 Request Failure 4xx (introduction) · Checked 2026-10-14
24. 24
    RFC 3261 defines 600 Busy Everywhere as the callee being busy and not wishing to take the call, to be returned only if the client knows no other end point such as voicemail will answer.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.6.1 600 Busy Everywhere · Checked 2026-10-14
25. 25
    RFC 3261 defines 603 Decline as the callee's machine being contacted successfully while the user explicitly does not wish to or cannot participate.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.6.2 603 Decline · Checked 2026-10-14
26. 26
    RFC 3261 says a 603 response is returned only if the client knows that no other end point will answer the request.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.6.2 603 Decline · Checked 2026-10-14
27. 27
    RFC 3261 allows a 603 response to indicate a better time to call in a Retry-After header field.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.6.2 603 Decline · Checked 2026-10-14
28. 28
    RFC 3261 says 6xx responses mean a server has definitive information about a particular user, not just the particular instance indicated in the Request-URI.

    RFC 3261 — SIP: Session Initiation Protocol · Section 21.6 Global Failures 6xx · Checked 2026-10-14
29. 29
    RFC 3261 says that on receiving a 6xx response a stateful proxy SHOULD cancel all pending client transactions in that response context and MUST NOT create new branches in it.

    RFC 3261 — SIP: Session Initiation Protocol · Section 16.7 Response Processing, step 5 Check response for forwarding · Checked 2026-10-14
30. 30
    RFC 3261 says that absent any 6xx response a proxy SHOULD choose the best response from the lowest response class stored in the response context.

    RFC 3261 — SIP: Session Initiation Protocol · Section 16.7 Response Processing, step 6 Choosing the best response · Checked 2026-10-14
31. 31
    RFC 3261 says that when choosing the best response to forward, a proxy MUST choose from 6xx class responses if any exist in the response context.

    RFC 3261 — SIP: Session Initiation Protocol · Section 16.7 Response Processing, step 6 Choosing the best response · Checked 2026-10-14
32. 32
    RFC 3398 maps a SIP 480 Temporarily Unavailable response to ISUP cause 18 No user responding.

    RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping · Section 8.2.6.1 SIP Status Code to ISDN Cause Code Mapping, row 480 · Checked 2026-10-14
33. 33
    RFC 3398 maps a SIP 486 Busy Here response to ISUP cause 17 User busy when interworking SIP to ISUP.

    RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping · Section 8.2.6.1 SIP Status Code to ISDN Cause Code Mapping, row 486 · Checked 2026-10-14
34. 34
    RFC 3398 maps a SIP 600 Busy Everywhere response to ISUP cause 17 User busy, the same cause as 486.

    RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping · Section 8.2.6.1 SIP Status Code to ISDN Cause Code Mapping, row 600 · Checked 2026-10-14
35. 35
    RFC 3398 maps a SIP 603 Decline response to ISUP cause 21 Call rejected.

    RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping · Section 8.2.6.1 SIP Status Code to ISDN Cause Code Mapping, row 603 · Checked 2026-10-14
36. 36
    RFC 3398 says that by default the cause location in the generated ISUP cause should be user for 6xx responses and network for 4xx and 5xx responses.

    RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping · Section 8.2.6.1 SIP Status Code to ISDN Cause Code Mapping, text following the table · Checked 2026-10-14
37. 37
    RFC 3398 maps ISUP cause 17 User busy received in a REL message to SIP 486 Busy Here.

    RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping · Section 7.2.4.1 ISDN Cause Code to Status Code Mapping, Normal event table, row 17 · Checked 2026-10-14
38. 38
    RFC 3398 maps ISUP cause 18 No user responding to SIP 408 Request Timeout, not to 480.

    RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping · Section 7.2.4.1 ISDN Cause Code to Status Code Mapping, Normal event table, row 18 · Checked 2026-10-14
39. 39
    RFC 3398 maps ISUP cause 19 No answer from the user and cause 20 Subscriber absent to SIP 480 Temporarily Unavailable.

    RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping · Section 7.2.4.1 ISDN Cause Code to Status Code Mapping, Normal event table, rows 19 and 20 · Checked 2026-10-14
40. 40
    RFC 3398 maps ISUP cause 21 Call rejected to SIP 403 Forbidden, noting that a 6xx code could be given instead when the cause location is user.

    RFC 3398: Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping · Section 7.2.4.1 ISDN Cause Code to Status Code Mapping, Normal event table, row 21 and (+) note · Checked 2026-10-14
41. 41
    RFC 4458 uses cause URI parameter value 408 for the redirecting reason No reply, which is the no-answer forwarding case.

    Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR) · Section 2.2 Cause, table · Checked 2026-10-14
42. 42
    RFC 4458 assigns cause URI parameter value 480 the redirecting reason Deflection immediate response, not no answer.

    Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR) · Section 2.2 Cause, table · Checked 2026-10-14
43. 43
    RFC 4458 defines a cause URI parameter value 486 meaning the redirecting reason User busy.

    Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR) · Section 2.2 Cause, table · Checked 2026-10-14
44. 44
    RFC 4458 shows a proxy retargeting a busy call to voicemail with a Request-URI carrying target set to the original user and cause=486, after receiving a 486 response.

    Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR) · Section 2 example URI; Section 6.1 call flow message F7 · Checked 2026-10-14
45. 45
    RFC 4497 Table 2 maps SIP 486 Busy Here to QSIG cause value 17 User busy, and no row in its SIP-to-QSIG table maps 486 to cause 34.disputed

    RFC 4497: Interworking between the Session Initiation Protocol (SIP) and QSIG · Section 8.4.4, Table 2 Mapping of SIP 4xx-6xx responses to an INVITE request to QSIG Cause values, row 486 · Checked 2026-10-14
46. 46
    RFC 4497 maps QSIG cause 21 Call rejected to SIP 603 Decline when the cause location indicates user, and to 403 Forbidden otherwise.

    RFC 4497: Interworking between the Session Initiation Protocol (SIP) and QSIG · Section 8.4.1, Table 1 Mapping of QSIG Cause Value to SIP 4xx-6xx responses, row 21 · Checked 2026-10-14
47. 47
    RFC 4497 maps QSIG cause 34 No circuit/channel available to SIP 503 Service Unavailable.

    RFC 4497: Interworking between the Session Initiation Protocol (SIP) and QSIG · Section 8.4.1, Table 1, row 34 · Checked 2026-10-14
48. 48
    RFC 5806, published with Historic status, lists Diversion header reasons including user-busy, no-answer and unavailable but defines no normative mapping from SIP response codes to those reasons.

    RFC 5806: Diversion Indication in SIP · Status of This Memo; Section 4 Extension Syntax; Section 9.1 · Checked 2026-10-14
49. 49
    RFC 6432 allows any SIP response except 100 Trying to carry a Reason header field with a Q.850 cause code.

    RFC 6432: Carrying Q.850 Codes in Reason Header Fields in SIP (Session Initiation Protocol) Responses · Section 3 · Checked 2026-10-14
50. 50
    RFC 6432 says the presence of a Q.850 Reason header field in a response does not change how the response is treated, and recommends integrity protection because a wrong cause can trigger wrong announcements.

    RFC 6432: Carrying Q.850 Codes in Reason Header Fields in SIP (Session Initiation Protocol) Responses · Section 4 · Checked 2026-10-14
51. 51
    RFC 7044 requires a SIP entity that retargets after an error response to include a Reason header field containing the SIP response code in the History-Info hi-targeted-to-uri, except for a Tel URI.

    RFC 7044: An Extension to the Session Initiation Protocol (SIP) for Request History Information · Section 10.2; Section 9.3 step 2 · Checked 2026-10-14
52. 52
    RFC 7044 says that when a request times out a SIP entity MUST update its History-Info cache as if it had received a 408 response.

    RFC 7044: An Extension to the Session Initiation Protocol (SIP) for Request History Information · Section 10.2 · Checked 2026-10-14
53. 53
    RFC 8197 states that 603 Decline can signal temporary unavailability such as being in a meeting and that no 4xx, 5xx or 6xx code before 607 signified that a request was unwanted.

    RFC 8197: A SIP Response Code for Unwanted Calls · Section 3 Motivation · Checked 2026-10-14
54. 54
    RFC 8197 defines 607 Unwanted so a called party can mark a call as unwanted, and receivers need do nothing beyond default 6xx handling though providers may use it for blocking or analytics.

    RFC 8197: A SIP Response Code for Unwanted Calls · Abstract; Section 4 · Checked 2026-10-14
55. 55
    RFC 8688 defines 608 Rejected so that a caller can tell a rejection by an intermediary such as a call analytics engine apart from a rejection by the called user.

    RFC 8688: A Session Initiation Protocol (SIP) Response Code for Rejected Calls · Abstract; Section 1 · Checked 2026-10-14
56. 56
    Twilio error 31480 Temporarily Unavailable covers a callee that is currently unavailable but also lists client network causes such as blocked UDP without TURN servers.

    31480: Temporarily Unavailable · 31480: Temporarily Unavailable > Possible causes · Checked 2026-10-14
57. 57
    Twilio error 31603 Decline is used for a callee that declined the call, and Twilio also lists SIP termination traffic on an inactive account as a cause of this code.

    31603: Decline · 31603: Decline > Possible causes; Possible solutions · Checked 2026-10-14
58. 58
    Twilio says a 486 Busy Here during call setup surfaces as error 31486, ends the dial attempt, and sets DialCallStatus to busy, which an action URL can use to route to voicemail, another number or a retry.

    31486: Busy Here · 31486: Busy Here > Possible causes; Possible solutions · Checked 2026-10-14
59. 59
    Twilio sets DialCallStatus to no-answer when the dialed party does not pick up before the Dial timeout, which defaults to 30 seconds with a range of 5 to 600 and an added five-second buffer.

    TwiML Voice: <Dial> · <Dial> attributes > timeout; action > DialCallStatus · Checked 2026-10-14

Documents

Cite this page

WarmTransfer. (2026, October 14). SIP 480 and 486 and 603 responses. WarmTransfer. https://warmtransfer.net/knowledge/sip-480-486-603-responses

@misc{warmtransfer-sip-480-486-603-responses,
  title  = {SIP 480 and 486 and 603 responses},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/sip-480-486-603-responses},
  note   = {Verified 2026-10-14}
}