The recent discussions around DSL over ISDN (IDSL) prompted to me to put a tutorial together on ADSL/IDSL qualification:
To understand when/if your line might qualify, consider this:
Initial I was very excited about the prospects of IDSL as I suspected it could easily serve as an interim solution for the other 45% of us. IDSL is a low-bandwidth version of DSL that runs at 144Kbps (upstream and downstream). It uses the EXACT same digital encoding protocol and frequencies as ISDN, therefore the signal CAN be run through USLC and IDLC remotes.
I had incorrectly assumed that ANYONE who qualifed for ISDN could also get IDSL (assuming there was a IDSL capable DSLAM in your central office). I now see that IDSL will NOT work in IDLC scenarios unless there is a IDSL DSLAM in the remote terminal---I suspect there are NONE installed. Since IDLC probably accounts for 25% of all loops, that means that it is not as ubiquitous as I suspected. However, I'd suspect that nearly half of those that don't qualify for ADSL, DO qualify for IDSL. Just realize that Bellsouth doesn't support IDSL, so you must seek out alternate IDSL providers (e.g. www.covad.com ).
This is also bad news for those in IFITL neighborhoods with no PCDATA (Fast Access over fiber) infrastructure (ME!). In my case, I qualify for ISDN, but all POTS service is provisioned through an IDLC. Even though Covad has a IDSL DSLAM in my CO, there is no way to get service---see diagrams on the above page for the details. Be forewarned, IDSL providers don't seem to have a way to know whether or not your loops are provisioned on IDLC. Two neighbors ordered IDSL through Zyan and Bignet, and they were both told they were qualified. Both orders are in "progress", but I already know the sad outcome.
Questions/comments/suggestions on the tutorials, please email me.
Would also be interested in talking with anyone actually using IDSL.