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

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Dial-up backup for Frame relay using PTSN

Hi folks,

Probably a real simple question and answer to this one, but I would like to see if i can get DDR happening if, and when the frame goes down between two 1720 routers. Id ideally like to use the Cisco WIC modems, but realise that this can be done using the AUX ports and standard modems.

Im looking for any help on this one, and any links to the TAC would be helpful. I cant seem to find the one I need and was hoping someone would have found it in their travels.

Secondly, If I use the WIC modems, does this give me full 56K V.90 symetrical data flow (56K up and down) rather than a Asymetrical 56K down and 33K up?? My understanding is that I can only get 33K if i connect 2 asymetrical modems back to back (ie one dials the other).

Currently Im not using sub serial interfaces for the frame as I have a very simple network, and its not envisaged that we are going to require further connections.The dial backup is purely as a frame backup, to keep comms happening. Most of our frame outages only last about 30 mins to 1 hours, so any more speed (ie ISDN) is really overkill.

Can anyone put me on the right track?? is there a simple way of testing this without bringing down the frame until Ive tested it and 99% certain it will dial on failure of the frame??

Any links, pointers and help will be most appreciated....

Many thanks


New Member

Re: Dial-up backup for Frame relay using PTSN

Long day...PSTN...not PTSN!!

Cisco Employee

Re: Dial-up backup for Frame relay using PTSN

Connecting two analog modems (using WIC-2AM or any 56K analog modems) over PSTN or POTS line will give you only V.34 (33K down) speed..

In order to get V.90 (56K down 33K up) you need digital modems and digital path at other side of PSTN( like T1 or E1)...Pl visit here for more info on that.

For backup, first evaluate which scheme will be the best for your netowork, here is the link which will help you to decide that

Now here is the link which discuss DDR backup using AUX to AUX port of the routers.

You can use "backup interface xxx" command instead of dialer-watch..

Another one

Useful link for DDR backup troubleshooting

New Member

Re: Dial-up backup for Frame relay using PTSN

Thanks very much for those links. I have some reading to do!!!.

Wish I could use the V.90 56K down, but the frame goes to a pretty remote area as well. Hence why we need to find a backup as it goes down pretty regular.

Is there such thing as an analogue modem that can be 'switched'?? ie swap the 56K down to a 56K up and vice versa???

Once again, thanks for the info.