SIP 415 Unsupported Media Type
AsteriskRFC 3261 §21.4.13The body's media type isn't supported. In SIP this almost always means the SDP carries a media line the receiver can't decode at all (vs. 488 which means "I understand it but can't accept these specific parameters"). Frequently seen on T.38 reinvites where the far end's stack doesn't understand `m=image udptl` as a media kind.
Common causes on Asterisk
- SDP `m=image udptl t38` reinvite hitting a peer that only speaks audio (some older Avaya / 3CX builds)
- Caller body is XML/JSON when the callee expects only SDP
- Wrong `Content-Type` header (e.g. `application/sdp` typo)
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