Appendix 16. Glossary
Internet Security Router User
’s Manual
144
See also DNS.
download
To transfer data in the downstream direction, i.e., from the Internet to the user.
DSL
Digital Subscriber Line
A technology that allows both digital data and analog voice signals to travel over
existing copper telephone lines.
Ethernet
The most commonly installed computer network technology, usually using twisted pair
wiring. Ethernet data rates are 10 Mbps and 100 Mbps. See also 10BASE-T,
100BASE-T, twisted pair.
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 the 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
Any method of protecting a computer or LAN connected to the Internet from intrusion or
attack from the outside. Some firewall protection can be provided by packet filtering
and Network Address Translation services.
FTP
File Transfer Protocol
A program used to transfer files between computers connected to the Internet.
Common uses include uploading new or updated files to a web server, and
downloading files from a web server.
hop
When you send data through the Internet, it is sent first from your computer to a router,
and then from one router to another until it finally reaches a router that is directly
connected to the recipient. Each individual
“leg” of the data’s journey is called a hop.
hop count
The number of hops that data has taken on its route to its destination. Alternatively, the
maximum number of hops that a packet is allowed to take before being discarded (see
also TTL).
host
A device (usually a computer) connected to a network.
HTTP
Hyper-Text Transfer Protocol
HTTP is the main protocol used to transfer data from web sites so that it can be
displayed by web browsers. See also web browser, web site.
ICMP
Internet Control Message Protocol
An Internet protocol used to report errors and other network-related information. The
ping command makes use of ICMP.
IGMP
Internet Group Management Protocol
An Internet protocol that enables a computer to share information about its membership in
multicast groups with adjacent routers. A multicast group of computers is one whose
members have designated as interested in receiving specific content from the others.
Multicasting to an IGMP group can be used to simultaneously update the address books
of a group of mobile computer users or to send company newsletters to a distribution list.
Internet
The global collection of interconnected networks used for both private and business
communications.
intranet
A private, company-internal network that looks like part of the Internet (users access
information using web browsers), but is accessible only by employees.
IP
See TCP/IP.
IP address
Internet Protocol address
The address of a host (computer) on the Internet, consisting of four numbers, each