Technologies that do not require a user to go through a dial-up procedure to connect to a service providers central office are referred to as always-on technologies. Attackers like these systems because they are always available to be attacked and to be used to attack others. Which of the following is not considered an always-on technology?

A.
ADSL

B.
Cable modem

C.
ISDN

D.
SDSL

Explanation:
ISDN emulates a dial-up connection and requires the user to go through
a dial-up procedure.