Short for ISDN Digital Subscriber Line, a method of providing DSL technology over existing ISDN lines. Even though the transfer rates for IDSL are about the same as ISDN (144kbps v. 128kbps), and IDSL circuits typically only carry data (not voice), the major benefits of switching to IDSL from ISDN are always-on connections, thus eliminating call setup delays; flat rate billing, instead of per minute fees; and transmission of data over the data network, rather than the PSTN.
IDSL was developed by Ascend Communications, now part of Lucent Technologies.
