5xx Range SIP Call Disconnect Troubleshooting

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When troubleshooting unexpected SIP call disconnects, it's essential to look at the SIP response codes to determine the reason for the disconnection. SIP (Session Initiation Protocol) is used to set up and manage voice and video calls in IP networks, and response codes are used to indicate the status of SIP requests.

The 5xx range of SIP response codes indicates server errors, which means that the SIP request was received and processed by the server, but an error occurred while handling the request. The following are the three SIP response codes from the 5xx range:

1. Service Unavailable (503) - The server is temporarily unavailable to process the request. This response code is usually returned when the server is overloaded or undergoing maintenance.

2. Internal Server Error (500) - The server encountered an unexpected condition that prevented it from fulfilling the request. This response code is usually returned when there is a server-side software or hardware issue.

3. Bad Gateway (502) - The server received an invalid response from another server while attempting to fulfill the request. This response code is usually returned when there is a problem with an intermediate server or gateway.

The other three response codes mentioned in the question are from the 4xx range, which indicates client errors. These codes indicate that the server was unable to fulfill the request due to a problem with the client's request or credentials.

4. Forbidden (403) - The client is not authorized to access the requested resource.

5. Unauthorized (401) - The client's request lacks valid authentication credentials for the target resource.

6. Request Timeout (408) - The client did not receive a timely response from the server.

In conclusion, when troubleshooting unexpected SIP call disconnects, it is crucial to check the SIP response codes, especially those in the 5xx range, to determine the cause of the problem.