Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

Dial-in capability of 804 ISDN router

Can the 804 router be used to accept regular incoming modem calls through the ISDN line and route to the LAN. Essentially I want to use the router as an access router for remote users. The users will not have ISDN modems, they will have regular modems.


Re: Dial-in capability of 804 ISDN router

Yep, you can do that.

What you need to do is to make the ISDN interface to accept all voice calls incoming on the interface as data calls. This technology is called DOV - Data Over Voice. Call initiator may be an analog modem connected to a PC. The ISDN bri interface is configured to accept these voice calls, but treat it as data.

For this, you will have to subscribe Voice service over the BRI line, from your provider. Provider will configure his switch to accept and send, voice calls. But to the end points, calls are initiated as voice calls, and data is send as voice.

One disadvantage of this, is that the provider might use voice signal manipulation, while switching from one switch to another, without affecting the voice quality, but the data might get really corrupted. So you might want to ask your provider about DOV support.

To configure DOV on your interface,

int bri 0/0

isdn incoming-voice data


Re: Dial-in capability of 804 ISDN router

This is incorrect.

If a modem is initiating the call, then a modem is required to terminate the call. The 2 modems together will train up and handle the modem layer protocols.

DOV is applicable when BOTH sides are making sync data (ie, not async analog) calls, yet you want the intermediate carriers to think/treat the call as if it is a voice call. Often times this is desired for tarif reasons; it may be cheaper to get voice service from your carrier than data.

As for the original question, I admit to not understanding it. The general question concerned an 804 router accepting modem calls. This is not possible, however if the calls were V.120 (async to sync conversion) then they would arrive at the 804 as a digital call, and this would work. This would require a device (normally a Terminal Adaptor that connects to a PC) to place the call. The TA can either place V.120 calls, or straight digital calls.

But then the question goes on to say that the remote "users will not have ISDN modems, they will have regular modems.". So I guess the remote users will be receiving the calls (since the 804 will be receiving the calls, and it does not have a modem), but the modem users will be placing the calls? Again, if that is the case the best bet is for the remote users to use a TA to place digital calls.


Re: Dial-in capability of 804 ISDN router

An analog modem call to an 804 router can only be successfully terminated by a real modem on one of the 804's POTS ports. Since the 804 lacks async ports (other than console), it cannot answer the call or otherwise provide connectivity. You would need another router or server to handle the digital side of the modem. That is, all the 804 could do would be to accept an incoming voice call from the ISDN switch and pass it on to the modem so the modem thinks it is attached to a normal analog line. It is not clear if this is what you are looking for. Also be aware that even though I have used modems and fax machines on an 804's POTS ports, last time I checked Cisco did not support modem usage with an 804, so there are no guarantees.

Good luck and have fun!

Vincent C Jones

CreatePlease to create content