ADSL (Asymmetric Digital Subscriber Line) - Transports information to and from
customers and networks. ADSL employs different upstream and downstream data
rates. The “asymmetric” name refers to these differing rates.

AH (Authentication Header) – RFC2402 defines AH. AH provides integrity and
authentication through the shared key hashing algorithms (HMAC-MD5, HMAC-
SHA1). AH provides authentication for as much of the IP header as possible. AH also
authenticates upper level protocol data.

AM (Amplitude Modulation) Modulation method used by modems, radio, and DSL
equipment. The signal modulates or alters the amplitude or intensity of the carrier. In
regular AM, the carrier is a sinewave. The amplitude of the modulated carrier changes
in proportion to signal amplitude. AM creates two identical sidebands on either side of
the carrier. These sidebands contain the signal data. Either sideband can be
attenuated or suppressed without harming the signal data. With an equivalent signal,
AM tends to require less bandwidth than FM does. AM's disadvantage is that it’s more
subject to impulse noise and static than FM is.

ATM (Asynchronous Transfer Mode) - Protocol that packs digital information into 53-
byte cells. The cells switch throughout a network over virtual circuits.

Average Cell Rate - Maximum sustainable or average rate (Cells/second) for sending
cells to the network. Average Cell Rate specifies bandwidth utilization. This value
must always be less than or equal to Peak Cell Rate.

file:///P|/T_WRITER/Documentation/Released/900...003%20(Guiness)%20prac%20template/glossary.htm (1 of 11) [11/6/2002 9:02:38 AM]

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