user manual

AT-TQ2403 Management Software User's Guide 279
trans
national authorities such as the Federal Communications Commission (FCC),
the European
Telecommunications Standards Institute (ETSI),
the Korean Communications Commission, or the Telecom
Engineering Center (TELEC).
CSMA/CA
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is a low-level network arbitration/
contention protocol. A station listens to the media and attempts to transmit a packet when the channel is
quiet. When it detects that the channel is idle, the station transmits the packet. If it detects that the channel
is busy, the station waits a random amount of time and then attempts to access the media again.
CSMA/CA is the basis of the IEEE 802.11e Distributed Control Function (DCF). See also RTS and CTS.
The CSMA/CA protocol used by 802.11 networks is a variation on CSMA/CD (used by Ethernet networks).
In CSMA/CD the emphasis is on collision detection whereas with CSMA/CA the emphasis is on collision
avoidance.
CTS
A clear to send (CTS) message is a signal sent by an IEEE 802.11 client station in response to a request to
send (RTS) message. The CTS message indicates that the channel is clear for the sender of the RTS message
to begin data transfer. The other stations will wait to keep the air waves clear. This message is a part of the
IEEE 802.11 CSMA/CA protocol. (See also RTS.)
D
DCF
The Distribution Control Function is a component of the IEEE 802.11e Quality of Service (QoS) technology
standard. The DCF coordinates channel access among multiple stations on a wireless network by controlling
wait times for channel access. Wait times are determined by a random backoff timer which is configurable by
defining minimum and maximum contention windows. See also EDCA.
DHCP
The Dynamic Host Configuration Protocol (DHCP) is a protocol specifying how a central server can
dynamically provide network configuration information to clients. A DHCP server "offers" a "lease" (for a
pre-configured period of time—see Lease Time) to the client system. The information supplied includes the
client's IP addresses and netmask plus the address of its DNS servers and Gateway.
DNS
The Domain Name Service (DNS) is a general-purpose query service used for translating fully-qualified
names into Internet addresses. A fully-qualified name consists of the hostname of a system plus its domain
name. For example, www is the host name of a Web server and www.alliedtelesis.com
is the fully-qualified
name of that server. DNS translates the domain name www.alliedtelesis.com
to some IP address, for
example 66.93.138.219.
A domain name identifies one or more IP addresses. Conversely, an IP address may map to more than one
domain name.
A domain name has a suffix that indicates which top level domain (TLD) it belongs to. Every country has its
own top-level domain, for example .de for Germany, .fr for France, .jp for Japan, .tw for Taiwan, .uk for the
United Kingdom, .us for the U.S.A., and so on. There are also .com for commercial bodies, .edu for
educational institutions, .net for network operators, and .org for other organizations as well as .gov for the
U. S. government and .mil for its armed services.
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