Copper Mountain DSLAMs support IDSL at 64 kbps, 128 kbps and 144 kbps payload data rates.

While we haven't had a chance yet to do any thorough examination of CM IDSL, we can already see one thing they've done as an extra twist relative to generic IDSL. Just like on SDSL they've made an extension to the standard startup sequence to convey the data rate for which the CPE should configure the bitpump so as to not have user configuration for it, they must have a corresponding mechanism for IDSL CPE to select between 64, 128 and 144 kbps modes, i.e., between using B1, B1+B2 or B1+B2+D out of the ISDN frame. CM IDSL CPE doesn't have any user configuration of the data rate either, especially the CopperRocket!

It appears that the mechanism for conveying the payload data rate on IDSL is via the ISDN EOC, i.e., they must have added a proprietary message or two. They use CMCP on IDSL as well, but since it's an in-band HDLC protocol, they have to get the HDLC link going at the correct data rate first, just like on SDSL.

How would CM's proprietary hacks in the ISDN EOC affect our open source generic IDSL CPE? Since it appears that CM had actually made an effort to make their SDSL interoperable with generic or vanilla CPE which doesn't understand the special CM quirks, let's hope that the same holds for IDSL and that CPE support for their proprietary EOC messages is optional as long as the user is willing to set the correct data rate manually.