ISDN
ISDN, or Integrated Services Digital Network, uses dedicated high-quality phone lines to provide higher internet access speeds than dial-up modems.
As new lines must be installed to provide the clarity required on the line for ISDN signals, this type of service is quite expensive and has generally been suited only for business use.
ISDN also tends to be reasonably slow compared to ADSL and only slightly faster than dial-up modems, with speeds ranging from 64Kbps up to 192Kbps. In fact it does not qualify as broadband based on common international standards.
With the widespread availability of faster and cheaper broadband solutions, ISDN is now largely used for specialised purposes and by companies who wish to be able to exchange digital information without having it accessible from the internet.