T-Comfort Comfort Pro S, Mounting And Commissioning Manual

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Fundamentals Voice over IP (VoIP)
Channels on a Media Gateway (MGW) are allocated for making a telephone connection with an ordinary
terminal or for dial tones. The MGW converts IP voice data into PCM data streams used with conventional
telephony and vice versa. For this, IP voice data are exchanged between the IP telephone and the gateway.
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Switching between voice data channels may cause a slight delay in some
circumstances. For example: when accepting a call on an IP telephone, headset users
should wait about one second before answering.
Useful Services
The type of data compression used for VoIP prevents these types of connections from using certain services.
Take these notes into account especially if you want to use connections made via Q.SIG-IP or SIP:
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ISDN data services can not be used
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Faxes can only be sent using the uncompressed G.711 codec
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DTMF dial tones are only received by the other party if the uncompressed G.711 codec is used.
Alternatively, DTMF dial tones can be transferred using the Internet standard RFC 2833/4733. For this,
the “DTMF (RFC4733)” codec needs to be activated for the codec configuration on the Telephony :
Extended : VoIP profile page.
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Analogue modems can not be used
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Configure the actual usage for the a/b ports, e.g. set them to Fax or Data (analogue) .
Connections from and to these a/b ports will then be made using uncompressed or
ISDN connections where possible.
Voice Activity Detection (VAD)
You can change the codec configuration under Telephony : Extended : VoIP profile . You can also activate the
Voice Activity Detection option for one or more codecs in so doing. If this option is active then pauses in the
conversation will be replaced with empty packets. This can be better compressed by compression-codecs
thus reducing the required bandwidth. This option must be deactivated if you want to assign the profile to a
SIP trunk and if you have set the G.711 codec.