415 4xx Client error RFC 3261
SIP 415 Unsupported Media Type
The message body is in a format the server does not support (for example, not application/sdp).
Typical Q.850 / ISDN cause: 79 (Service or option not implemented)
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Common causes
- A body type the far end does not accept, such as multipart/mixed with ISUP, or a SIP MESSAGE content type.
How to fix it
- Check the Accept and Content-Type headers. Remove the SIP-I/ISUP body on interconnects that don't support it.
Seeing 415 on calls through a router or firewall? Check that SIP ALG is disabled. It causes a surprising number of SIP errors. Read why.
About 4xx responses
The request has a problem or cannot be completed at this server, usually because of something on the requesting side or the target user.