Linksys WAP54G Quick Installation Manual page 63

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.
Driver - A workstation or server software module that provides an interface
between a device and the upper-layer protocol software running in the comput-
er; it is designed for a specific device, and is installed during the initial instal-
lation of a network-compatible client or server operating system.
DSSS (Direct-Sequence Spread-Spectrum) - DSSS generates a redundant bit
pattern for each bit to be transmitted. This bit pattern is called a chip (or chip-
ping code). The longer the chip, the greater the probability that the original data
can be recovered. Even if one or more bits in the chip are damaged during
transmission, statistical techniques embedded in the radio can recover the orig-
inal data without -the need for retransmission. To an unintended receiver, DSSS
appears as low power wideband noise and is rejected (ignored) by most nar-
rowband receivers.
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.
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Instant Wireless ® Series Wireless-G Access Point
Dynamic IP Address - An IP address that is automatically assigned to a client
station in a TCP/IP network, typically by a DHCP server. Network devices that
serve multiple users, such as servers and printers, are usually assigned static IP
addresses.
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 - More than one BSS in a 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
the center frequency of a conventional carrier several times per second accord-
ing to a pseudo-random set of channels, while chirp spread spectrum changes
the carrier frequency. Because a fixed frequency is not used, illegal monitoring
of spread spectrum signals is extremely difficult, if not downright impossible
depending on the particular method.
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.
Fragmentation - Breaking a packet into smaller units when transmitting over
a network medium that cannot support the original size of the packet.
Gateway - A device that interconnects networks with different, incompatible
communications protocols.
Hardware - Hardware is the physical aspect of computers, telecommunica-
tions, and other information technology devices. The term arose as a way to dis-
tinguish the "box" and the electronic circuitry and components of a computer
from the program you put in it to make it do things. The program came to be
known as the software.
Hub - The device that serves as the central location for attaching wires from
workstations. Can be passive, where there is no amplification of the signals; or
active, where the hubs are used like repeaters to provide an extension of the
cable that connects to a workstation.
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