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      List of SIP response codes

      Here’s a detailed list of SIP response codes as they apply to SkySwitch (NetSapiens PBX), along with insights specific to how they handle calls.

       

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      100 Trying

      • Meaning: The SkySwitch PBX has received the SIP request and is attempting to process it.
      • Usage in SkySwitch:
        • Seen in outbound call logs when dialing through SkySwitch SIP trunks.
        • If the call hangs at this stage, it might indicate a routing issue or an unresponsive trunk.

      180 Ringing

      • Meaning: The destination VoIP device is ringing.
      • Usage in SkySwitch:
        • If 180 is missing, check if early media is being used (183 Session Progress instead).
        • If you hear a ringback but don’t see 180, the provider might be sending early media instead of a SIP response.

      181 Call Is Being Forwarded

      • Meaning: The call is being redirected to another destination.
      • Usage in SkySwitch:
        • If a call is forwarded via PBX rules (e.g., Find Me/Follow Me), you may see 181 before the next INVITE.

      182 Queued

      • Meaning: The call is waiting in a queue before routing.
      • Usage in SkySwitch:
        • Often seen in call center or hunt group environments.

      183 Session Progress

      • Meaning: Call is in progress with early media (audio before answering).
      • Usage in SkySwitch:
        • Used for call announcements, ringback tones, or IVRs before the call is answered.

      2xx - Success Responses

      These indicate that the request was successfully processed.

      200 OK

      • Meaning: Call setup was successful.
      • Usage in SkySwitch:
        • Received when a call is answered.
        • Seen in successful SIP registrations.

      202 Accepted

      • Meaning: The request is accepted for processing but not completed.
      • Usage in SkySwitch:
        • May appear if external API or third-party integrations are processing the call asynchronously.

      204 No Notification

      • Meaning: Request processed successfully, but no further action is needed.
      • Usage in SkySwitch:
        • Rarely used but may appear in certain SIP message exchanges where no response is required.

      3xx - Redirection Responses

      These indicate that further action is needed to reach the recipient.

      300 Multiple Choices

      • Meaning: Multiple destinations exist for the request.
      • Usage in SkySwitch:
        • If a user has multiple devices registered, the system may respond with 300 to indicate multiple available endpoints.

      301 Moved Permanently

      • Meaning: The user’s location has changed permanently.
      • Usage in SkySwitch:
        • Seen if an extension has been reassigned or permanently forwarded.

      302 Moved Temporarily

      • Meaning: The user is temporarily available at a different address.
      • Usage in SkySwitch:
        • Common in call forwarding settings.

      305 Use Proxy

      • Meaning: A proxy server is required for routing.
      • Usage in SkySwitch:
        • Seen in carrier-level call routing when a different outbound proxy is required.

      380 Alternative Service

      • Meaning: Another service is available to complete the call.
      • Usage in SkySwitch:
        • Typically used when a call is redirected to a different call-handling service.

      4xx - Client Error Responses

      These indicate that the request contained an error or cannot be fulfilled by the recipient.

      400 Bad Request

      • Meaning: The request contains a syntax error.
      • Usage in SkySwitch:
        • Happens if an outbound call is malformed or contains an invalid header.

      401 Unauthorized

      • Meaning: Authentication is required.
      • Usage in SkySwitch:
        • Common in SIP registration failures (e.g., when a SIP trunk requires credentials).

      403 Forbidden

      • Meaning: The server refuses to fulfill the request.
      • Usage in SkySwitch:
        • If a user is trying to dial a restricted number, SkySwitch returns 403 Forbidden.

      404 Not Found

      • Meaning: The requested SIP extension or number does not exist.
      • Usage in SkySwitch:
        • Can indicate:
          • A nonexistent extension.
          • A deactivated SIP trunk.
          • A routing misconfiguration.

      407 Proxy Authentication Required

      • Meaning: Authentication is required at the proxy level.
      • Usage in SkySwitch:
        • Appears when SIP trunks require authentication.

      408 Request Timeout

      • Meaning: No response was received from the called party.
      • Usage in SkySwitch:
        • Often indicates a network issue or unresponsive endpoint.

      480 Temporarily Unavailable (DND - Do Not Disturb)

      • Meaning: The user is unavailable.
      • Usage in SkySwitch:
        • Used when Do Not Disturb (DND) is enabled.

      486 Busy Here

      • Meaning: The user is actively on a call.
      • Usage in SkySwitch:
        • Appears if the extension is already on another call.

      487 Request Terminated

      • Meaning: The request was canceled.
      • Usage in SkySwitch:
        • Seen if the caller hangs up before the recipient answers.

      488 Not Acceptable Here

      • Meaning: Media negotiation failed.
      • Usage in SkySwitch:
        • Seen in codec mismatches between endpoints.

      5xx - Server Error Responses

      These indicate that the server encountered an issue.

      500 Server Internal Error

      • Meaning: A generic server failure.
      • Usage in SkySwitch:
        • Often indicates PBX misconfigurations.

      503 Service Unavailable

      • Meaning: The service is down or unavailable.
      • Usage in SkySwitch:
        • Appears if the SIP trunk provider is unreachable.

      504 Server Timeout

      • Meaning: The SIP request timed out.
      • Usage in SkySwitch:
        • Happens when carrier networks are slow to respond.

      6xx - Global Failure Responses

      These indicate a global rejection of the request.

      600 Busy Everywhere

      • Meaning: The recipient is busy on all devices.
      • Usage in SkySwitch:
        • Used if a user has multiple devices and all are busy.

      603 Decline

      • Meaning: The call was manually rejected.
      • Usage in SkySwitch:
        • Sent if a user presses "Reject" on their phone.

      604 Does Not Exist Anywhere

      • Meaning: The number does not exist in the entire SIP system.
      • Usage in SkySwitch:
        • Common when a user dials an invalid number.

      607 Unwanted (Spam Call Blocked)

      • Meaning: The recipient has blocked the caller.
      • Usage in SkySwitch:
        • Used when a call is blocked due to spam detection or user preferences.

      Summary of SkySwitch-Specific Behavior

      • 480 Temporarily Unavailable = DND Mode
      • 486 Busy Here = User is on a call
      • 603 Decline = Manual Call Rejection
      • 607 Unwanted = Blocked Call
      • 404 Not Found = Number doesn’t exist or PBX misconfigured
      • 503 Service Unavailable = SIP Trunk Down