VOIP - Modem support on remote gateway

Unanswered Question
Nov 12th, 2007


I'm trying to find a solution for the following: we need to provide modem support in a remote office, that will only have IP connectivity. The analog line will be provided in the HQ building.

How could we use a modem in the remote office to dial out via the analog line in HQ?

This solution will be CCME based for telephony, and there might be an additional gateway when needed for this.

Would modem passthrough help us out? What would the setup look like then? Connect a gw with FXO interface in HQ to the PSTN line (might be a TDM-PBX breakout, but should be fine also), and put another GW with an FXS interface in the remote office to connect the modem to?

Any ideas, hints, tips&tricks?


I have this problem too.
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smahbub Fri, 11/16/2007 - 10:28

Media Gateway Control Protocol (MGCP) and Simple Gateway Control Protocol (SGCP) are call control protocols that run between call agents (CA) and gateways in a packet telephony network.

As in the earlier implementations of the two protocols, a gateway handles the translation between audio signals and the packet network. These gateways interacts with a CA, also called a Media Gateway Controller (MGC), which performs signal and call processing on the gateways' calls. Support has expanded to include:

dfyen Fri, 11/16/2007 - 16:17

Hi Chris,

ATAs are sometimes a solution in putting faxes in the LAN (not the most stable solution if I may add), but these do not support modems, only analog phones and faxes.

The VG224/248 support modems, but this is quite an overkill for only 1 connection.

kind regards,


Paolo Bevilacqua Sat, 11/17/2007 - 02:06

Depend what do you mean by "work".

If you are happy with 9.6 or 14.4 speeds, that doable for sure. Sometime faster connections have been reported, but I would never design based on the assumption these would work.

Thanks for the reply. In some situations you don't even need the connectivity you outlined. If they're in an Ethernet environment and still need modem support, it's probably more related to SCADA or some control system or reporting process over modem (I'm guessing). At least, that is where I've run into it before.

So, if the systenm consistently supports 9600, it may well be good enough for this application (the one I work with connects at 2400 by design!).


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