What Does ISDN Digital Subscriber Line Mean?
ISDN Digital Subscriber Line (IDSL) is a technology that provides DSL over an ISDN line. IDSL transmits data at a rate of 144 kbps and was originally developed by Ascend Communications, which was acquired by the company that is now Alcatel-Lucent.
Techopedia Explains ISDN Digital Subscriber Line
IDSL is basically a cross between xDSL and ISDN. Transfer rates are slightly higher than ISDN (144 kbps vs 128 kbps), but much slower than standard DSL connections. In addition, a major benefit of switching to IDSL from ISDN is the always-on connection.