SIP Response Codes: Troubleshooting VoIP Call Failures
When a SIP call fails, the server returns a three-digit response code similar to HTTP status codes. Understanding these codes speeds up troubleshooting.
1xx: Provisional Responses
Codes like 100 Trying and 180 Ringing indicate the call is in progress. They are informational, not errors.
2xx: Success
200 OK means the call or registration succeeded. If calls work but a related feature fails, the issue is usually elsewhere.
4xx: Client Errors
404 Not Found means the dialed number or extension does not exist. 401 Unauthorized and 403 Forbidden point to authentication problems. 486 Busy Here indicates the called party is busy. 408 Request Timeout suggests network or reachability issues.
5xx: Server Errors
500 Internal Server Error, 502 Bad Gateway, and 503 Service Unavailable usually indicate a problem with the PBX, gateway, or carrier. Check server health and trunk status.
6xx: Global Failures
Codes like 600 Busy Everywhere and 604 Does Not Exist Anywhere indicate the call cannot be completed anywhere.
Redstone management interfaces expose SIP logs and registration status to support troubleshooting.
Redstone Systems, Inc. founded in Delaware, USA in December 2002, has been the ODM vendor for many well-known communications companies, serving the Southeast Asian market. In 2020, Redstone Systems will begin to return to the North America market with its self-developed brand.
Redstone has a complete product line of intelligent voice gateways, providing IP-PBXs, analog VoIP gateways (FXS/FXO), digital VoIP gateways (E1/T1), border appliances, and session boundary controllers (SBCs).
With advanced technology in digital signal processor (DSP), speech coding and speech processing, as well as efficient operational tools such as cloud remote management, auto provisioning, Redstone gateways are widely used in markets of enterprise communications, cloud communications, call centers, operators’ IMS/SIP trunks, bringing users friendly, efficient and reliable communication experience.
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