Final Status Code
Understand the Final Status Code metric — how CallMeter records the SIP response code that ends each call, and what different status codes reveal about call success or failure.
Final Status Code records the SIP response code that concluded the call, such as 200 OK (success), 486 Busy Here, 408 Request Timeout, or 503 Service Unavailable. This single value tells you whether the call succeeded and, if it failed, exactly why.
Think of it as the call's exit code. Just as a program returns a code when it finishes — 0 for success, non-zero for error — a SIP call ends with a response code that categorizes the outcome.
One-shot metric
Final Status Code is captured once per call. It appears in the Call Timing Overview cards on the endpoint detail page.
How It Works
During a SIP call, multiple response codes may be exchanged (100 Trying, 180 Ringing, etc.). The final status code is the last definitive response that determines the call's outcome:
- 2xx (Success) — Call was answered. 200 OK is the standard success response.
- 3xx (Redirection) — Call was redirected to another destination.
- 4xx (Client Error) — Call failed due to a problem with the request. Includes busy (486), not found (404), unauthorized (401/407), and request timeout (408).
- 5xx (Server Error) — Call failed due to a server-side problem. Includes service unavailable (503) and server internal error (500).
- 6xx (Global Failure) — Call rejected everywhere. Includes decline (603) and busy everywhere (600).
CallMeter records the final response code and makes it available for filtering, aggregation, and analysis.
Why It Matters
The final status code is the foundation for two critical telecom KPIs:
- ASR (Answer Seizure Ratio) — Percentage of calls that received a 2xx response. Low ASR indicates call completion problems.
- NER (Network Effectiveness Ratio) — Percentage of calls that received either a 2xx or a user-refusal (486, 603). Low NER indicates infrastructure problems distinct from user behavior.
For enterprise testing:
- Infrastructure health — 5xx errors indicate server problems. A spike in 503 responses means the SIP infrastructure is overloaded.
- Routing validation — 404 responses mean the destination was not found. 484 means the address was incomplete.
- Authentication testing — 401/407 responses indicate authentication failures.
- Load testing — Tracking status code distribution under increasing load reveals the failure mode of your infrastructure.
Common Status Codes
| Code | Meaning | Typical Cause |
|---|---|---|
| 200 | OK (Success) | Call answered normally |
| 408 | Request Timeout | Remote side did not respond in time |
| 480 | Temporarily Unavailable | Destination registered but not answering |
| 486 | Busy Here | Destination is on another call |
| 487 | Request Terminated | Call cancelled by the caller |
| 488 | Not Acceptable Here | Codec or media negotiation failed |
| 500 | Server Internal Error | SIP server encountered an error |
| 503 | Service Unavailable | Server overloaded or out of service |
| 603 | Decline | Destination actively refused the call |
For a comprehensive reference of all SIP response codes, see the SIP Response Codes reference.
How to Fix It
- Group by status code — Aggregate final status codes across a test run to see the distribution. A healthy test should have predominantly 200 OK responses.
- Investigate 4xx errors — Client errors often indicate configuration issues: wrong credentials (401/407), invalid destination (404), or incompatible codecs (488).
- Address 5xx errors — Server errors require infrastructure investigation. 503 Service Unavailable often means the SIP server has reached its capacity.
- Check for timeouts — A high rate of 408 Request Timeout suggests the remote side is unreachable or overloaded.
- Validate codec compatibility — 488 Not Acceptable Here means the endpoints could not agree on a codec. Review the SDP offer/answer to find the mismatch.
Related Metrics
- Call Result — Human-readable interpretation of the final status code
- Post-Dial Delay (PDD) — Calls that timeout have high PDD before the final status code
- Call Setup Time — Only meaningful for calls with a 200 OK final status
- Call Duration — Only meaningful for answered calls (2xx status)
RFC Reference
SIP response codes are defined in RFC 3261 (SIP: Session Initiation Protocol), Section 21. Response classes (1xx through 6xx) are organized by category in Sections 21.1 through 21.6. Additional response codes are defined in various SIP extension RFCs.
Call Duration
Understand Call Duration measurement — how CallMeter tracks the connected time of a test call, and what duration reveals about test scenario execution and SLA compliance.
Call Result
Understand the Call Result metric — how CallMeter classifies call outcomes into human-readable categories, and what each result type means for test success and infrastructure health.