Linksys WAP55AG User Manual page 23

Database - A database is a collection of data that is organized so that its con-
tents can easily be accessed, managed, and updated.
Data Packet - One frame in a packet-switched message. Most data communi-
cations is based on dividing the transmitted message into packets. For example,
an Ethernet packet can be from 64 to 1518 bytes in length.
Default Gateway - The routing device used to forward all traffic that is not
addressed to a station within the local subnet.
DHCP (Dynamic Host Configuration Protocol) - A protocol that lets network
administrators manage centrally and automate the assignment of Internet
Protocol (IP) addresses in an organization's network. Using the Internet's set of
protocol (TCP/IP), each machine that can connect to the Internet needs a
unique IP address. When an organization sets up its computer users with a con-
nection to the Internet, an IP address must be assigned to each machine.
Without DHCP, the IP address must be entered manually at each computer and,
if computers move to another location in another part of the network, a new IP
address must be entered. DHCP lets a network administrator supervise and dis-
tribute IP addresses from a central point and automatically sends a new IP
address when a computer is plugged into a different place in the network.
DHCP uses the concept of a "lease" or amount of time that a given IP address
will be valid for a computer. The lease time can vary depending on how long a
user is likely to require the Internet connection at a particular location. It's espe-
cially useful in education and other environments where users change fre-
quently. Using very short leases, DHCP can dynamically reconfigure networks
in which there are more computers than there are available IP addresses.
DHCP supports static addresses for computers containing Web servers that
need a permanent IP address.
Download - To receive a file transmitted over a network. In a communications
session, download means receive, upload means transmit.
DSSS (Direct-Sequence Spread Spectrum) - DSSS generates a redundant bit
pattern for all data transmitted. This bit pattern is called a chip (or chipping
code). Even if one or more bits in the chip are damaged during transmission,
statistical techniques embedded in the receiver can recover the original data
without the need for retransmission. To an unintended receiver, DSSS appears
as low power wideband noise and is rejected (ignored) by most narrowband
receivers. However, to an intended receiver (i.e. another wireless LAN end-
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Instant Wireless ® Series Dual-Band Wireless A + G Access Point
point), the DSSS signal is recognized as the only valid signal, and interference
is inherently rejected (ignored).
DTIM (Delivery Traffic Indication Message) - A DTIM field is a countdown
field informing clients of the next window for listening to broadcast and mul-
ticast messages. When the AP has buffered broadcast or multicast messages for
associated clients, it sends the next DTIM with a DTIM Interval value. AP
Clients hear the beacons and awaken to receive the broadcast and multicast
messages.
Encryption - A security method that applies a specific algorithm to data in
order to alter the data's appearance and prevent other devices from reading the
information.
ESS (Extended Service Set) - A set of more than two or more BSSs (multiple
access points) forming a single network.
Ethernet - IEEE standard network protocol that specifies how data is placed
on and retrieved from a common transmission medium. Has a transfer rate of
10 Mbps. Forms the underlying transport vehicle used by several upper-level
protocols, including TCP/IP and XNS.
FHSS (Frequency Hopping Spread Spectrum) - FHSS continuously changes
(hops) the carrier frequency of a conventional carrier several times per second
according to a pseudo-random set of channels. Because a fixed frequency is not
used, and only the transmitter and receiver know the hop patterns, interception
of FHSS is extremely difficult.
Firewall - A firewall is a set of related programs, located at a network gateway
server, that protects the resources of a network from users from other networks.
(The term also implies the security policy that is used with the programs.) An
enterprise with an intranet that allows its workers access to the wider Internet
installs a firewall to prevent outsiders from accessing its own private data
resources and for controlling what outside resources to which its own users
have access.
Basically, a firewall, working closely with a router, examines each network
packet to determine whether to forward it toward its destination.
Firmware - Code that is written onto read-only memory (ROM) or program-
mable read-only memory (PROM). Once firmware has been written onto the
ROM or PROM, it is retained even when the device is turned off.
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