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Chapter 9
Glossary
A
Address mask
A bit mask used to select bits from an Internet address for subnet addressing. The
mask is 32 bits long and selects the network portion of the Internet address and
one or more bits of the local portion. Sometimes called subnet mask.
AAL5
ATM Adaptation Layer - This layer maps higher layer user data into ATM cells,
making the data suitable for transport through the ATM network.
ADSL
Asymmetrical Digital Subscriber Line is an asymmetrical technology, meaning that
the downstream data rate is much higher than the upstream data rate. ADSL
operates in a frequency range that is above the frequency range of voice services,
so the two systems can operate over the same cable.
ATU-C and ATU-R
ADSL Transmission Unit, Central or Remote: the device at the end of an ADSL line
that stands between the line and the first item of equipment in the subscriber
premises or telephone switch. It may be integrated within an access node.
