ISDN stands for Integrated Services Digital Network. It is used to bridge the Central Office's local loop and the premise connection (home). ISDN uses the existing wiring so that no new cabling is required. It is a digital service that restores the analog plain old telephone set.
An Integrated Digital Network (ISDN) is a network in which digital switching connections are used to transmit digital signals. Integrated Services refers to ISDNs ability to deliver two simultaneous connections, in any merging of data, voice, video and fax, over an individual line. Multiple devices can be connected to the line and sent as needed.
An ISDN is a network, in general evolving from telephony ISDN, which provides end-toend digital connectivity to provide a broad range of services such as voice and non-voice services, to which customers have to create by a limited set of standard multipurpose user network interfaces.