SIP Rejection Code Hunting Policies

Alex_Sberna — Tue, 02 Jun 2026 16:00:34 GMT

The Sinch Elastic SIP Trunking product hunts through endpoints in order of priority whenever the customer’s infrastructure rejects, or fails to respond to, a SIP Invite request.

4XX: By default, we will not hunt on 4XX errors except for the following codes:

Code	Reason	Default behavior
403	Forbidden	Hunt
404	Not Found	Hunt
408	Request Timeout	Hunt
415	Unsupported Media Type	Hunt
420	Bad Extension	Hunt
421	Extension Required	Hunt
422	Session Interval Too Small	Hunt
423	Interval Too Brief	Hunt
436	Bad Identity Info	Hunt
437	Unsupported Certificate	Hunt
438	Invalid Identity Header	Hunt
480	Temporarily Unavailable	Hunt
48	Request Terminated	Hunt
488	Not Acceptable Here	Hunt
491	Request Pending	Hunt
493	Undecipherable	Hunt

5XX: We will always continue hunting on a 5XX error

Code	Reason	Default behavior
500	· Internal Server Error	Hunt
503	· Service Unavailable	Hunt
504	· Server Timeout	Hunt

article SIP Rejection Code Hunting Policies in Elastic SIP Trunking

SIP Rejection Code Hunting Policies

4XX: By default, we will not hunt on 4XX errors except for the following codes:

5XX: We will always continue hunting on a 5XX error

6XX: We will not continue hunting after receiving a 6XX error