Open Forum → DSL and ISDN Interference?

My DSL installer told me recently that there was a good chance that my SDSL service wouldn't work, or would sync at a speed lower than the 768K I ordered, since I also have an ISDN line.

The SDSL line will run next to the ISDN and my voice line underground, and into the phone box (or NID or demarc) in the garage, but will NOT run near the ISDN from that point on.

Does this guy know what he's talking about? Is it likely that my ISDN line will cause interference with the SDSL line?

Thanks!

In my unscientific hunt for an answer, I found this:

quote:

---

Finally, there's concern that ADSL lines sharing the same cable bundle with T1, ISDN, HDSL, or possibly other ADSL wire pairs will experience some level of crosstalk. Spectral compatibility with T1 services isn't a big issue in suburban and rural America, but many metropolitan subscribers may be sharing a wire bundle with a nearby business that has a T1 or ISDN line.

Also, Europe and Asia have lots of residential ISDN lines, which will require some accommodation to coexist with ADSL. For example, ISDN lines employ 2B1Q encoding in the U.S., and 4B/3T encoding in Germany to deliver 128 kbits/s to homes and offices. Both schemes have spectral components that extend up to 100 kHz, well into the normal ADSL band. Recent analysis has shown that ADSL must relocate its operation above 80 kHz to become compatible with the 2B1Q coding scheme used in many U.S. T1 lines. Solutions under consideration include shifting up the entire ADSL spectrum, or simply turning off the bottom five or so tones.

---

This is from a rather good but old page: http://www.elecdesign.com/magazine/1998/oct2298/comtech/1022ct1.shtml

At the time I had my ADSL line installed from Sprint, I also had an ISDN line. We couldn't get the ADSL line to sync, so the Sprint Tech thought it might have something to do with the ISDN line. He disabled the ISDN line and it didn't make a difference. In the end we got the line to sync, but the installer said that the ISDN line shouldn't have anything to do with an ADSL line not working. As a matter of fact I asked him whether it would degrade my service and he said "no, it shouldn't". This is from my Telco, Sprint, so I don't know if that makes a difference or not.

Ran into a few situations like this in the field... So far the only thing i have been able to find out is in the way of how the CO is setup(what type of hardware is running their side of things, One Provider here in my state is moving all existing equipment from one Manufacturer to another because of similair problems of this nature) the switching of equipment has reduced these kind of problems.. So without relaying to much info... If your CO is setup with Hardware A it may not be affected at all. If Hardware B is used, this may cause some problems for certain areas. Some states make it a requirement for all CO's to run compatible if not the same equipment in uniform. I the southwest up till DSL lines came into the arena.. they have whatever, wherever, whenever and are working hard at coming up with a standard.
Hope this helps...

------------------
DSL Installer/Tech/Web Dev
Always looking to help....

I have seen ADSL work within the same 25 pair binder as T1 and IDSN. But, I have also seen it not work in the same 25 pair binder. I think it realy has to do with how good of a signal the DSL is.
ADSL can handle some RFI.
It takes your bandwidth (upstream and downstream) and it splits into 256 mini channels. It then monitors these channels for problems. When it sees that a channel is having RFI it will shut off that channel and bit stuff the data into other channels.

It is possible for ISDN to interfere with SDSL, because they run on the same lower frequencies (which is why SDSL can't be run on the same line as voice), but whether it will or not depends on the amount of crosstalk between the wiring.

ADSL is less likely to have problems because it can shift the frequencies it uses, thereby lessening the effect of interference.

OK, so it's possible that there will be a problem. I may be able to give up my ISDN line, and get a second DSL line to connect to my employer's network.

It seems that the two DSL lines may interfere with each other as well, correct?

Thanks for the help!

It is possible, but there is a very good chance that you won't have any trouble anyway, because if the cables are twisted and in decent shape, it shouldn't interfere.

Not that I have seen.
Engineers here like to put all the ADSL lines in the same 50 pair group.
So I would have to say no, ADSL lines will not have problems with each other. Or at least that I have seen.

[This message has been edited by Zane0 (edited 16 June 2000).]