Mitel MiVOICE BUSINESS, Инструкция по инженерии

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Network Configuration Specifics
267
DTMF SIGNALLING OVER IP NETWORKS
Generally, DTMF tones are used to establish a call between two end point at the start of a call.
These tones are detected by the end equipment or connected interface and information is sent
via the signalling channel, or out-of-band to the voice channel, which is yet to be established.
This is normal DTMF usage.
However, there are instances where DTMF signals may be sent in-band (within the voice
channel) after a call has been set up. In-band DTMF signals may be impacted (lost or altered
due to packet loss or jitter) when passed over an IP network. To counteract this possibility, the
DTMF signals are carried through the IP network as RFC4733 DTMF.
RFC4733 is intended to work with analog devices or TDM interfaces that use telecom dialing
and timings for DTMF digits. However, certain speed dialing devices—e.g. Alarm monitors and
Point of Sales (POS) terminals—may send or expect to receive DTMF digits that differ from
standard telecom practices. Such devices may suffer performance degradation when used over
a voice over IP connection, i.e. in-band signalling.
Use of such speed dialing devices should be considered as best-effort and may work in some
situations, but not others. Should these devices suffer degradation, some suggestions include
changing the dialing characteristics on the end devices, or use an alternative directly IP
connected device, effectively as an overlay network onto the same IP infrastructure.
Connections to the PSTN should terminate on an analogue or digital TDM trunk. The same
logic applies to SIP trunks as well as IP trunks.
T.38 FOIP GUIDELINES
T.38 is the protocol recommended by the ITU to allow for transmission of real-time Group 3
Fax transmission over IP networks.
Mitel's T.38 implementation support V.17 speeds. Fax calls that are v.34 based will be handled
at V.17 speeds by the 3300 ICPs.
T.38 is not supported on any of the server platforms, since it is a conversion between TDM and
IP transmission, and these platforms do not have any TDM lines or trunks. T.38 is supported
on the following platforms:
• 3300 MXe
• 3300 CX/CXi
• 3300 CX/CXi II
• 3300 AX
WARNING:MODEM SIGNALS REQUIRE A SPECIAL CONNECTION SETUP TO
BE SENT OVER AN IP NETWORK; AS A RESULT, IT IS NOT RECOMMENDED
TO SEND MODEM SIGNALS OVER AN IP NETWORK AT THE PRESENT TIME.
WARNING:DUE TO THE UNRELIABILITY OF SENDING MODEM DATA OVER AN
IP NETWORK, THIS TYPE OF CONNECTION SHOULD NEVER BE USED FOR
ANY KIND OF CRITICAL APPLICATION SUCH AS ALARM SYSTEMS.