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On our fleet of SNOM D713 phones we don't get any ringback tones when making outgoing calls - mainly to mobile numbers. Despite having a managed service by an external party, they are convinced they have solved the problem every time we have reported this yet nothing changes. 

I have the admin access to our backend but can't clearly see which setting may be affecting this. If anyone has any ideas that would be amazing.

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Jordan Moore

End user

Joined: 14.03.2025

1 Comment

  1. Snom Jan Boguslawski

    Hi Jordan,

    such symptoms indicate that a service provider (must not be the direct one) is not signaling 180 Ringing / 183 Progress +SDP in a reliable manner.

    Usally in attempts to call mobile phones it takes more time and several handover points between providers / networks etc. Therefore it is important that some sort of Progress indication is send back to the phone initiating the call, - so it can play the locally generated or the ringback from SDP by the provider.

    In your case e.g. it is possible that 183 Progress with SDP is signalled - but no SDP is transmitted to the D713, - or nothing is signaled at all...

    So you typically make call attempt, here nothing (full silence), wait & wait and without any announcement you hear the mobile phone user speaking.

    Not sure if it helps in your case (as more diagnostic / SIP trace is needed) but you can try to workaround testing with the following settings:

    rtp_early_media_playback - Snom Service Hub - Snom Confluence

    and related: rtp_early_media_ring_fallback - Snom Service Hub - Snom Confluence

    in the latter setting website the SIP Example may help you to better understand the issue regarding 180 and 183 signaling.

    Please note, even if the workaround may help - the "root cause" remains the service side signaling / or not signaling of 180/183.

    Thanks, and greetings from Berlin,

    Jan