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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.
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.
Dual-Band Wireless Access Point
3938
Instant Wireless
TM
Series
considered by the buffer designer. Like a cache, a buffer is a "midpoint hold-
ing place" but exists not so much to accelerate the speed of an activity as to
support the coordination of separate activities.
CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) - In local
area networking, this is the CSMA technique that combines slotted time-divi-
sion multiplexing with carrier sense multiple access/collision detection
(CSMA/CD) to avoid having collisions occur a second time. This works best if
the time allocated is short compared to packet length and if the number of sit-
uations is small.
CSMA/CD (Carrier Sense Multiple Access/Collision Detection) - The LAN
access method used in Ethernet. When a device wants to gain access to the
network, it checks to see if the network is quiet (senses the carrier). If it is not,
it waits a random amount of time before retrying. If the network is quiet and
two devices access the line at exactly the same time, their signals collide. When
the collision is detected, they both back off and each wait a random amount of
time before retrying.
CTS (Clear To Send) - An RS-232 signal sent from the receiving station to the
transmitting station that indicates it is ready to accept data.
Database - A database is a collection of data that is organized so that its con-
tents can easily be accessed, managed, and updated.
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-