Integrated Services Digital Network (ISDN)
ISDN has long been an alternative to the slower modem WAN connections but at a higher cost. ISDN allows the transmission of voice and data over the same physical connection.
ISDN connections are considerably faster than regular modem connections. To access ISDN, a special phone line is required, and this line is usually paid for through a monthly subscription. You can expect these monthly costs to be significantly higher than those for traditional dial-up modem connections.
To establish an ISDN connection, you dial the number associated with the receiving computer, much as you do with a conventional phone call or modem dial-up connection. A conversation between the sending and receiving devices is then established. The connection is dropped when one end disconnects or hangs up. The line pickup of ISDN is very fast, allowing a connection to be established, or brought up, much more quickly than a conventional phone line.
ISDN has two defined interface standardsBasic Rate Interface (BRI) and Primary Rate Interface (PRI).