Integrated Services Digital Network (ISDN) is made up of digital telephony and data-transport services that are offered by local telephone carriers.
ISDN often involves digitization of telephone network that allows voice, data, text, graphics, music, video, and any other source material to be transmitted over to any existing telephone wire.
ISDN Adapter is a device that allows a computer to transmit over ISDN lines. ISDN lines are digital telephone lines that are capable of transferring speeds in the range from 57.6K to 128K. They provide two data channels, each having its own phone number that allow simultaneous voice and data as well as higher speed data transfers using both lines for data.
There are two basic types of ISDN service:
Basic Rate Interface (BRI): this is the basic service and is intended to meet the needs of most individual users, and
Primary Rate Interface (PRI): it is intended for users with greater capacity requirements.
ISDN adapters operate at the Data Link layer of the OSI model.
