Modem Relay

Unanswered Question
Jan 9th, 2008
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Dear All

my company needs to support the customers through dialup connections and there is no any analog phone line ready.

can any one help me how i can use the modem relay or any thing to solve this problem.

i have 2811 gateway.


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Overall Rating: 4.4 (7 ratings)
paolo bevilacqua Mon, 01/14/2008 - 00:28
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Instead of using modem relay, suggest thta you use one of the "virtual com" programs available to emualt COM port over telnet. This way, your modemd-equipped device can be anywere and the ports shared by everyone.

hope this helps, please rate post if it does!

paolo bevilacqua Mon, 01/14/2008 - 02:20
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Hi, I have to say, the low rating given to my post is very wrong, because what I've suggested is the best solution for using originating and receiving modem from anywhere in the network, usig the async ports or modem modules in a router, as you will find yourself.

If your requirement is different, please explain it, or at least discuss, before using the rating system in a such inappropriate manner.

islam.irshaid Mon, 01/14/2008 - 02:32
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First of all sorry for miss undestanding me

about me i know what you suggested and i used dialout/EZ Program with Access Sever.

But i am in need to know how to configure the Modem relay and which type of client should use.

Thanks and Sorry

paolo bevilacqua Mon, 01/14/2008 - 03:00
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I'm not aware of any client for modem relay under windows. The cisco implementation allow port-to-port modem relay between cisco routers, and I don't think it supports third-party devices.

pcameron Mon, 01/14/2008 - 05:12
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Paolo's earlier response about the posting rating higlights something that all people asking for assistance need to understand.

If you want a good answer, you need to give a good problem description.

Many of the people who donate their time and expertise on these forums are able to give immediate solutions provided they have an understanding of the problem. If the intial problem description is vague, then the answer may be similarly vague and possibly not what was wanted.

When anyone posts a question on Netpro, write it up from the point of view that if someone asked you a technical question , what would you want them to provide so you can give a solution ?

In other words, tell us -

A detailed description of what you want the system to do

How you want it to work

A detailed description of the fault

Did the system ever work ? If so , what changed ?

If there is a problem, when does it happen?

Is there a trigger to make the problem happen

What have you already tried to rectify the problem ?

IOS versions, configs from equipment and any background details that may be relevant.

Here is the original problem description -

my company needs to support the customers through dialup connections and there is no any analog phone line ready.

can any one help me how i can use the modem relay or any thing to solve this problem.

i have 2811 gateway.

Unfortunately this doesn't tell us a lot about what you really want to do.

To give you a proper answer, we need to know -

How many modem calls do you need to handle on the system ?

Do you want to originate dial connections from the router ?

Do you wish to terminate dial connections directly on the router ?

Do you want the modem calls to transit the router to remote dial up modems via modem passthrough or modem relay ?

If you want to use modem relay/passthrough, what kind of latency and bandwidth does the connecting network have ?

What speeds do you expect the modems to work at ?

Do you have analogue (loop start) lines , or digital connections ?

If it is digital, do you have T1, E1 or ISDN Basic Rate connections ?

If you use T1 or E1, is it CAS or PRI?

So ... if we had all this kind of information in the original posting, quite possibly someone here could provide a reply that would rate a 5.0!

For anyone reading this, please keep these points in mind when you write up your questions - the more detail you can give, chances are you will get the right answer.

In the meantime, perhaps the new PVDM2 digital modems might be what you are looking for -

These new modem modules allow you to terminate and originate modems calls through digital trunks (E1, T1, BRI) directly on the router. The digital modems can be shared with normal voice calls if you also have PVDM2 voice modules installed - you use modem pooling to associate the modems to specific DNIS (called numbers) , the voice calls are directed to normal dial peers.

There are also analogue modem WIC's that will terminate a loop start analogue line on the router -

The comm port redirectors that Paolo suggested earlier are very useful in these kind of applications to redirect comm port traffic as telnet sessions direct to the router, the modems then pass the traffic as necessary.

If you want to use modem passthrough, remember you need a matching voip capable device with voice ports (router with FXS ports, ATA etc ...) to connect the remote modems to the IP network. Therefore it often makes sense to terminate the modems directly on the router using the digital modem modules instead of tunneling the calls across the IP cloud.

islam.irshaid Mon, 01/14/2008 - 05:33
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First, Thank you for the above informations.

Simply, i need to make dial up connection from my PC, but there is no an analog line avilable in my room,as i asked before if i can make a dialup connection like (DialoutZ Program)the connection will be digital from my PC to the Gateway then the gateway send it as analog signal,Yes Sir there is E1 PRI in our company.

pcameron Mon, 01/14/2008 - 05:51
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Ok, now we are getting an understanding of your issue :-)

So you have a PC that needs to make dial out conections.

Since you don't have an analogue line with the PC, you only have network access to the router.

In this case, Modem passthrough would not help unless you want to run a second ethernet connection to run an ATA or similar (or install a switch) AND you installed a modem card in the PC to connect to the ATA.

So if you want a simple dial in/out type access and there is a PRI connected already to the router (I am assuming for voice operation), then then best option is likely use the PVDM2 digital modem module in the router chassis and either use a comm port redirector or direct telnet/ssh to the router for dial in/out access on the E1 trunk. The modem call will be 'digital' in the sense the 'analogue' modem tones are passed as PCM, so it work with standard V90/V34bis etc ... type modems. Select a PVDM2 digital modem module depending on the number of simultaneous calls you wish to make.

Running a modem connection in this way means you would get anything up to V90 speeds (56Kbps) whereas modem passthrough can be very hit and miss in terms of connection speeds - in a lot of cases 19.2Kbps is regarded as a reliable speed for passthrough !

Rob Huffman Mon, 01/14/2008 - 06:51
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Hey Guys,

Just thought I would weigh-in for a moment :)

Paul, 5 points for this excellent description of what any "trouble report" should detail - Classic!

Paolo, 5 points for your continued and most valued participation here!

Thanks to both of you, these Forums become more and more helpful!

Take care,


marikakis Mon, 01/14/2008 - 09:57
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I could not agree more with Rob and I give my '5's to Paul and Paulo as well.

Keep up the good work!

Kind Regards,



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