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authorPhilipp Maier <pmaier@sysmocom.de>2018-10-01 15:37:05 +0200
committerPhilipp Maier <pmaier@sysmocom.de>2018-10-01 16:50:01 +0200
commit903e0f62a5508ca140babbe5ba157f7fc3cb9c25 (patch)
tree6eaa94e6e89211e2475dc0427c3e0c5bb12d8cd3
parent734e0ea24c11ab6fde7bcca886ba0af04571b77f (diff)
mncc: add note about DTMF considerations
Add an informative note on how DTMF signalling is done in mobile networks and mention the limitations regarding DTMF, when internal MNCC is used. Change-Id: Iedcf4ad5e0e4697c6a05ebdd4f43173c14c7c448 Related: OS#2777
-rw-r--r--common/chapters/mncc.adoc26
1 files changed, 26 insertions, 0 deletions
diff --git a/common/chapters/mncc.adoc b/common/chapters/mncc.adoc
index 8825be3..3adbf7f 100644
--- a/common/chapters/mncc.adoc
+++ b/common/chapters/mncc.adoc
@@ -60,6 +60,32 @@ MNCC interface compatible with the Osmocom MNCC socket is `lcr`, the Linux Call
Router. More widespread integration of external call routing is available via
the OsmoSIPConnector.
+
+=== DTMF considerations
+
+In mobile networks, the signaling of DTMF tones is implemented differently,
+depending on the signaling direction. A mobile originated DTMF tone is
+signaled using START/STOP DTMF messages which are hauled through various
+protocols upwards into the core network.
+
+Contrary to that, a mobile terminated DTMF tone is not transfered as an out of
+band message. Instead, in-band signaling is used, which means a tone is injected
+early inside a PBX or MGW.
+
+When using {program-name} with its built in MNCC functionality a mobile
+originated DTMF message will not be translated into an in-band tone. Therefore,
+sending DTMF will not work when internal MNCC is used.
+
+For external MNCC, the network integrator must make sure that the back-end
+components are configured properly in order to handle the two different
+signaling schemes depending on the signaling direction.
+
+NOTE: osmo-sip-connector will translate MNCC DTMF signaling into sip-info
+messages. DTMF signaling in the opposite direction is not possible.
+osmo-sip-connector will reject sip-info messages that attempt to signal
+a DTMF tone.
+
+
=== MNCC protocol description
The protocol follows the primitives specified in 3GPP TS 04.07 Chapter 7.1.