Howto:Howto get an analog modem to work with an analog adapter

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Revision as of 15:07, 10 June 2009 by Afi (talk | contribs) (info about V7 sync added)
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Analog adapters IP21/IP22/IP24/IP28/IP302 are able to work with an analog modem with some special settings.

Applies To

This information applies to

  • IP21 V5, V6
  • IP22 V6, V7
  • IP24 V6, V7
  • IP28 V6, V7
  • IP302 V6, V7


More Information

Problem Details

Sending Faxes over IP networks is only possible with an T.38 implementation like innovaphone uses in all Gateways. For modems there is no protocol implemented. The only way to get a working modem connection is to setup a media channel with no restriction or compression.


System Requirements

To enable fax or modem connection over RTP media channel following requirements must be fulfilled:

a network connection with no packet loss
LAN is only acceptable connection for this application, WAN is usually not able to fulfil the requirement
a network connection with low delay
LAN connection and frame size of 20 ms is required
the voice data must be uncompressed
G711 codec must be used exclusive
TDM-like synchronisation between endpoints
enables stable connection over longer period of time(available in V7)


Configuration

Following parameters that differ from the default configuration can be changed to increase the modem functionality.


Enable passive checkbox under TELx->Signaling (don't interpret FLASH and DTMF's when connected) on your appropriate TEL Interface:

Analog modem 01.png


Configure uncompressed codec G711 and frame size of 20 ms under Gateway/Interfaces/TELx:

Analog modem 02.png


Disable the echo canceler in the appropriate routing entry. Therefore go to the routing table Gateway->Routes:

Analog modem 03.png


Disable Echo Canceler for routes from and to appropriate analog interface:

Analog modem 04.png


Please keep in mind to deactivate echo canceller on whole voip path till outbreak to another analog line.


In Firmware Version 7 it is possible to get TDM Sync from remote device via IP. Make sure all devices are synchronized to device connected to the device with a TDM sync source like ISDN network.


Known Problems

Having still problems with Modem connections - disable faststart (no faststart) on the Gateway.

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