SIP 488 Not Acceptable Here vs 606 Not Acceptable
SIP 488 and 606 both reject a session due to incompatible parameters (codecs, media types), but they differ in scope. A 488 means this endpoint cannot accept the session parameters but another endpoint might; a 606 means no endpoint for this user can accept them.
Description
The request was understood but the session description (SDP) is not acceptable. The response may contain a list of acceptable media parameters.
Quand vous le voyez
When codec negotiation fails — the callee cannot handle any of the codecs offered in the SDP. Common in interop scenarios.
Comment résoudre
Check the Warning header or SDP in the response for acceptable parameters. Add compatible codecs (e.g., G.711 as a fallback) to your offer.
Description
The user's agent was contacted successfully but some aspects of the session description (SDP) are not acceptable. Unlike 488, this is a global failure — no other server can satisfy this request.
Quand vous le voyez
When the callee definitively cannot accept any of the offered media types or codecs. Different from 488 which is location-specific.
Comment résoudre
Check the Warning header or response body for which session parameters are unacceptable. Modify the SDP offer to use compatible codecs and media types.
Différences clés
488 is endpoint-specific — the session parameters are unacceptable at this UA, but another device may support them.
606 is a global rejection — the user cannot accept these session parameters on any device.
488 is a 4xx response; 606 is a 6xx global failure that terminates all forked branches.
488 typically indicates codec or media type mismatch at one endpoint.
606 should include an Accept, Accept-Encoding, or Accept-Language header listing what the user can accept.
Quand utiliser lequel
Return 488 when an endpoint cannot handle the offered SDP (codec mismatch, unsupported media type) but the user might have other endpoints that can. Return 606 when the user definitively cannot accept the session parameters on any device. Include acceptable alternatives in the 606 response headers.