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Glossary
120 EN/LZT 108 6492 R2 - October 2003
The DNS system is, in fact, its own network. If one DNS server doesn't
know how to translate a particular domain name, it asks another one, and
so on, until the correct IP address is returned.
Domain name
A domain name is a user-friendly name used in place of its associated IP
address
Downstream
The direction of a downstream signal is from the ISP/service provider to the
user's computer (downloading).
DSL
Short for Digital Subscriber Line, which is a data communications
technology that transmits information over the existing copper telephone
lines (POTS). DSL takes existing voice cables that connect customer
premises (CPE) to the phone company's central office (CO) and turns them
into a high-speed digital link. There are many types of DSL and ADSL is
one of them.
- E -
Encapsulation
A technology that enables one network to send its data via another
network's connections. Encapsulation works by encapsulating a network
protocol within packets carried by the second network. Encapsulation is
also called tunneling.
Ethernet
A local-area network (LAN) architecture that uses a bus topology and
supports data transfer rates of 10 Mbps. It is one of the most widely
implemented LAN standards.
A newer version of Ethernet, called 100Base-T (or Fast Ethernet), supports
data transfer rates of 100 Mbps. And the newest version, Gigabit Ethernet,
supports data rates of 1 gigabit (1,000 megabits) per second.
- F -
Filtering
To screen out selected types of data, based on filtering rules. Filtering can
be applied in one direction (upstream or downstream) or in both directions.
Filtering rule
A rule that specifies what kinds of data a routing device will accept and/or
reject. Filtering rules are defined to operate on an interface (or multiple
interfaces) and in a particular direction (upstream, downstream or both).
Firewall
A system designed to prevent unauthorized access to or from a private