System Hold music played after reciving "Media Attribute (a): sendonly " from SIP provider

When a call dialed to an invalid number through Service provider SIP trunk it responds with a “183 Session Progress” with Media Attribute (a): sendonly in the message body. This seems to put the line hold and play system default hold music for the user.

When analysing the call capture using wireshark there is RTP stream after the “183 Session Progress” which contains the correct recording received from the provider.

Is there is configuration from asterisk that can be used to avoid this? Or is this a issue with the service provider ?

Thanks in advance

System : Asterisk 18 + FreePBX16

This is expected behaviour. Sending a=sendonly is the standard way of indicating a SIP session is on hold. I’m not sure if a configuration option has been added to cope with the rare cases where the media is expected to be forwarded. I might have a look later. This certainly wasn’t an option in earlier versions of Asterisk.

Always passing media through would break holds initiated by normal SIP phones.

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Is it possible to pass through Operator MOH without replacing it with asterisk system default ?

You could try moh_passthrough. There is also a function to control this dynamically

I don’t think this was ever added to the legacy channel driver…

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Adding moh_passthrough to the trunk configuration didn’t have any effect.

moh_passthrough : true

moh_passthrough would have to be set on the non-provider end, as that is where the music on hold is injected.

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