Some (many) carriers only allow one-way audio from the switch to the caller so that you don’t get free phone calls. Early media is the part of the call that is not billed. If they allow the caller to send audio to the switch during this free period it would open them up to fraud. Bote From: Dmitriy Borisov Sent: Saturday, 30 January, 2016 15:19 Subject: [Freeswitch-users] DTMF capture and early media Hi, All! https://tools.ietf.org/html/rfc3960 has next part: Early media refers to media (e.g., audio and video) that is exchanged before a particular session is accepted by the called user. Within a dialog, early media occurs from the moment the initial INVITE is sent until the User Agent Server (UAS) generates a final response. It may be unidirectional or bidirectional, and can be generated by the caller, the callee, or both. Typical examples of early media generated by the callee are ringing tone and announcements (e.g., queuing status). Early media generated by the caller typically consists of voice commands or dual tone multi-frequency (DTMF) tones to drive interactive voice response (IVR) systems. But I know that in FreeSWITCH in preanswer state I can`t capture DTMF. Why? This part of RFC is conflicting with some other standard? It can be very intresting feature. -- С уважением, Борисов Дмитрий Отдел облачных технологий 1С-Рарус Тел. +7 (495) 231-20-02 доб.: 15-94 -- with best regards, Dmitriy Borisov 1C-Rarus Cloud Services tel.: +7 (495) 231-20-02 add.: 15-94