y codes, city codes, area codes, prefixes, and the subscriber number. ADM (add/drop multiplexer) A device that facilitates easy dropping and adding of pay- load by converting one or more lower-level signals, such as T-1 or E-1 signals, to and from one of the optical carrier levels. administrative domain A collection of hosts, routers, and networks governed by a single administrative authority. ADPCM (Adaptive Differential Pulse Code Modulation) An encoding technique, standardized by the ITU-T, that allows analog voice signals to be carried on a 32Kbps digital channel. The voice input is samples at 8KHz with 4 bits used to describe the difference between adjacent samples. ADSL (Asymmetrical Digital Subscriber Line) A technology for supporting high band- width over conventional twisted-pair local loop lines that enables subscribers to access multimedia- based applications such as video-on-demand. ADSL supports a downstream channel of up to 7Mbps, with an upstream channel of up to 800Kbps. ADSL2 A technology standardized under ITU G.992.1 that supports a downstream channel of up to 12Mbps and an upstream channel of up to 1Mbps. ADSL2+ A technology standardized under ITU G.992.5 that supports a downstream channel of up to 24Mbps and an upstream channel of up to 1Mbps. ADSL2-RE A reach-extended version of the ADSL2 specification that is standardized under ITU G.992.3. ADSL2-RE allows DSL systems to reach up to 3.75 miles (6 km). While it can sup- port up to 8Mbps downstream and 1Mbps upstream, when taking advantage of its main feature, ADSL2-RE extends a 768Kbps downstream service by approximately 0.5 mile (1 km), to 3.5 miles (5.5 km). AES (Advanced Encryption Standard) An encryption algorithm for securing sensitive material, both unclassified and classified, by U.S. government agencies; replaces the previously sanctioned standard, DES. It may eventually become the de facto encryption standard for com- mercial transactions in the private sector. AES uses the Rijndael algorithm to specify three key lengths-128 bits, 1