I am trying to determine how to connect a device that has an internal modem across a VOIP service connected through a cable modem. Currently, the devices dial across the PSTN and connect to a Cisco AS5350. Then the connection is made to the servers that store the data. Can the modem connect frequencies get through the VOIP system and then send the data stream?
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To run a modem over a VoIP system you have to ensure that echo cancellation is disabled and that compression is not in use (must use G.711). Some gateways automatically detect fax and modem tones and disable echo cancellation and compression for the call while others do not. If both are disabled and there is very little packet loss, you should be able to connect without any problems and pass data.
This was first published in April 2005