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Important Information
90 EN/LZT 108 6377 R4 - September 2003
DNS
Short for Domain Name System (or Service), an Internet service that
translates domain names into IP addresses. Because domain names are
alphabetic, they're easier to remember. The Internet however, is really
based on IP addresses. Every time you use a domain name, therefore, a
DNS service must translate the name into the corresponding IP address.
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 name that identifies one or more IP addresses. For example, the domain
name microsoft.com represents about a dozen IP addresses. Domain
names are used in URLs to identify particular Web pages. Because the
Internet is based on IP addresses, not domain names, every Web server
requires a Domain Name System (DNS) server to translate domain names
into IP addresses.
DOS attack
DOS (Denial of service) attack is a method of flooding a site with "spoofed"
(artificially generated) packets. A DOS tries to generate enough traffic deny
service to legitimate users. One recent method has been called "smurfing".
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.
DSLAM
Short for Digital Subscriber Line Access Multiplexer, a mechanism at a
phone company's central location that links many customer DSL
connections to a single high-speed ATM line. When the phone company
receives a DSL signal, an ADSL modem with a POTS splitter detects voice
calls and data. Voice calls are sent to the PSTN, and data are sent to the
DSLAM, where it passes through the ATM to the Internet, then back
through the DSLAM and ADSL modem before returning to the customer's
PC.