ISDNDigital Subsciber Line (IDSL) is a variant of the various xDSL processes with the evolution towards ISDN. The DSL process is standardized by the International Telecommunications Union( ITU) and the European Telecommunications Standards Institute( ETSI) and is ISDN-compatible in two versions: ISDN BRA (Basic Rate Access) and ISDN PRA (Primary Rate Access), i.e., for the basic access and for the primary multiplex access.
In the ISDN BRA IDSL variant, the upstream and downstream data rate is 128 kbit/s each, as with the ISDN basic rate access, or it is 64 kbit/s plus POTS, the analog trunk call, and 16 kbit/s for signaling. In the variant for the primary multiplex connection, both data rates are also identical and amount to 1,920 kbit/s plus 64 kbit/s for signaling. Both IDSL variants can bridge transmission distances of up to 5 km. 2Q/1B coding is used as the line code.
The IDSL method is suitable for connecting individual workstations to a central node on a separate site. This cost-effective approach uses all existing ISDN installations for data transfer; i.e. ISDN cards,routers andterminal adapters. IDSL can be used for file transfer, e-mail, access to the Internet, transaction processing and as a backup for leased lines.