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

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Innovaphone devices has no V.150 relay protocol implemented - the stable transport of modem data via IP, like in fax with T.38 is not possible. Analog adapters IP21/IP22/IP24/IP28/IP302 and Gateways IP810, IP0010, IP3010, IP6010, IP1060, may able to transport analog modem data via RTP channel with some special settings on innovaphone devices.


Applies To

This information applies to data modem transmissions over IP (and also for fax transmissions if T.38 is not enabled). Screen shots are for V8, but the logic applies to all versions.

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)


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:


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


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


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


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

It is recommended to disable T.38 on a route to/from a port with a modem device connected.

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.

Some modems cannot different speeds but only accept the speed set for the COM port used. In this case, try to set the COM port baud rate to a lower value (e.g. 9600 baud).

Newer Gateway Platforms

Newer gateway Platforms such as IP810, IP0010, IP3010, IP6010, IP1060, IP22/24/28, IP30x, IP38 feature automatic modem detect and bypass. With these devices, there is no need to explicitly disable the echo canceller. It is still necessary to configure TDM sync, set passive mode, disable T.38 and set the Codec to G711 with 20ms packet size.

Known Problems

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

Modem over IP is not reliable. Try to avoid, eg. using dedicated analogue lines or PRI/BRI to POTS splitter (such as an IP302 BRI->2*POTS).

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