Archived:SIP RTP/AVP connections result in a "415, unsupported media type" error on the remote end (Known Issue)
Registering an application to the SIP stack for RTP/AVP connections will result in an 415/Unsupported media type error on the remote end.
It is not possible to have two ECom plug-ins registered to handle the same media type. The first one installed will always handle or reject the incoming requests. As the native SIP phone application is registered to handle RTP/AVP it is not possible to re-register for this media type.
One can use a unique Accept-Contact header (but the same RTP/AVP media type) in the SIP message. Ideally, the Accept-Contact header is a better way of resolving the client as it can always be unique. This will route the messages to the correct applications. The problem that can arise from using this workaround solution is that a non-standard SIP message is being used.