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ProtocolCodes
606
SIP

606 Not Acceptable

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.

On this page

When You See This Code

When the callee definitively cannot accept any of the offered media types or codecs. Different from 488 which is location-specific.

How to Fix

Check the Warning header or response body for which session parameters are unacceptable. Modify the SDP offer to use compatible codecs and media types.

Specification

View RFC / Specification →

Comparisons

SIP 488 Not Acceptable Here vs 606 Not Acceptable

Compare With

100 Trying 180 Ringing 181 Call Is Being Forwarded 182 Queued 183 Session Progress 199 Early Dialog Terminated 200 OK 202 Accepted 204 No Notification 300 Multiple Choices 301 Moved Permanently 302 Moved Temporarily

Guides

401 Unauthorized vs 403 Forbidden: When to Use Each Security & Authentication
SIP Response Codes: Understanding VoIP Call Flow Real-Time Protocols
SIP Call Flow: Understanding Session Setup Real-Time Protocols
WebRTC Signaling with SIP and WebSocket Real-Time Protocols
RFC 3261: SIP Protocol Deep Dive Protocol Deep Dives
TLS 1.3: Faster, Simpler, More Secure Protocol Deep Dives

Debugging Scenarios

488 Not Acceptable Here — Codec Mismatch Advanced

Glossary

Status Code Request Method (HTTP Verb) TLS Handshake Authentication TCP/IP Port Number NAT (Network Address Translation) Socket Request-Response Model RFC (Request for Comments) Connection-Oriented Full-Duplex SRV Record SIP Dialog Signaling SIP Registrar STUN (Session Traversal Utilities for NAT) TURN (Traversal Using Relays around NAT) SDP (Session Description Protocol) SIP INVITE SIP Proxy Server SIP Redirect Server SIP Transaction SIP User Agent SIP Trunk RTP (Real-time Transport Protocol) SRTP (Secure Real-time Transport Protocol) SIP ACK SIP BYE SIP CANCEL SIP OPTIONS SIP SUBSCRIBE/NOTIFY B2BUA (Back-to-Back User Agent) SBC (Session Border Controller) Codec Negotiation SIP Response Classes VoIP (Voice over IP) Presence (SIP) PBX (Private Branch Exchange) MFA (Multi-Factor Authentication) TLS Versions

Frequently Asked Questions

What is SIP 606 Not Acceptable?

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.

When do you see SIP 606 Not Acceptable?

When the callee definitively cannot accept any of the offered media types or codecs. Different from 488 which is location-specific.

How to fix SIP 606 Not Acceptable?

Check the Warning header or response body for which session parameters are unacceptable. Modify the SDP offer to use compatible codecs and media types.