running: Add note about DTMF support
osmo-sip-connector does not yet support full DTMF support. The current implementation only supports DTMF tones to be send from MNCC to SIP, but not in the opposite direction. Change-Id: I578e50b0a42d88b05cf6da80443b71494b5eb26f Related: OS#2777
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@ -56,3 +56,29 @@ mncc
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socket-path /tmp/msc2_mncc
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----
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=== DTMF signaling
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In VoIP based telephony networks DTMF (Dual-tone multi-frequency signaling) can
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be signaled through multiple methods. Common methods are in-band, RFC2833 and
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sip-info messages.
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Osmo-sip-connector is using sip-info messages to signal DTMF tones. When a DTMF
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tone is signaled at the MNCC socket interface, osmo-sip-connector will generate
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a matching sip-info message to forward the DTMF signal to the PBX. Depending on
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the PBX software reconfiguring the DTMF signaling method to sip-info may be
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necessary.
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While sending DTMF tones through the MNCC interface to a SIP leg, the current
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implementation of osmo-sip-connector does not support sending DTMF tones in the
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opposite direction. Any attempts to send DTMF tones to an MNCC leg will be
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confirmed with a status 405 "Method not allowed".
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The reason for this limitation is that in mobile networks, depending on the
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signaling direction, the signaling of DTMF tones is implemented differently.
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A mobile originated DTMF tone is signaled through out of band messages,
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which arrive at osmo-sip-connector on as MNCC DTMF START/STOP messages. Those
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messages can be directly translated to sip-info messages. However, in the
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other direction (mobile terminated), an in-band signaling method is used. This
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means that osmo-sip-connector would have to translate an incoming DTMF sip-info
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message into an audio sample that then would have to be injected into the
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voice stream. Currently this scheme is not implemented in osmo-sip-connector.
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