10BaseT: An IEEE standard (802.3) for operating 10 Mbps Ethernet
networks (LANs) with twisted pair cabling and a wiring hub.
Ad-Hoc Mode: A client setting that provides independent peer-to-peer
connectivity in a wireless LAN. An alternative set-up is where PCs communicate
with each other through an AP. See AP and Infrastructure Mode.
AP (Access Point): A hardware device, or software used in conjunction
with a computer, that serves as a communications "hub" for wireless clients
and provides a connection to a wired LAN. An AP can double the range of
wireless clients and provide enhanced security.
Application software: A software program running on top of the
operating system (Windows, UNIX, Mac) that has been created to perform
a specific task for a user. Examples include word processing software
like Word/Word Perfect, spreadsheets like Excel or Lotus 123, home finance
packages like Quicken, etc.
Client: Any computer connected to a network that requests services
(files, print capability) from another member of the network.
CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance):
CSMA/CA is the principle medium access method employed by IEEE 802.11
WLANs. It is a "listen before talk": method of minimizing (but not eliminating)
collisions caused by simultaneous transmission by multiple radios. IEEE
802.11 states collision avoidance method rather than collision detection
must be used, because the standard employs half duplex radios—radios capable
of transmission or reception—but not both simultaneously. Unlike conventional
wired Ethernet nodes, a WLAN station cannot detect a collision while transmitting.
If a collision occurs, the transmitting station will not receive an ACKnowledge
packet from the intended receive station. For this reason, ACK packets
have a higher priority than all other network traffic. After completion
of a data transmission, the receive station will begin transmission of
the ACK packet before any other node can begin transmitting a new data
packet. All other stations must wait a longer pseudo randomized period
of time before transmitting. If an ACK packet is not received, the transmitting
station will wait for a subsequent opportunity to retry transmission.
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 free. If it is not,
it waits a random amount of time before retrying. If the network is free
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.
DSSS and FHSS:
Wireless LAN products are available in three different technologies --
direct-sequencing spread-spectrum (DSSS), frequency-hopping spread-spectrum
(FHSS) and infrared. DSSS and FHSS are spread-spectrum techniques that
operate over the radio airwaves in the unlicensed ISM band (industrial,
scientific, and medical). DSSS uses a radio transmitter to spread data
packets over a fixed range of the frequency band. FHSS uses a technique
by which the signal transmitted hops among several frequencies at a specific
rate and sequence as a way of avoiding interference. WECA’s focus is on
the use of DSSS for 11 Mbps high rate wireless LAN communications.
Ethernet:
The most widely used LAN access method, which is defined by the IEEE 802.3
standard. Ethernet is normally a shared media LAN meaning all devices
on the network segment share total bandwidth. Ethernet networks operate
at 10Mbps using CSMA/CD to run over 10BaseT cables.
Gateway:
A network point that acts as an entrance to another network.
Hz (Frequency) (Hertz):
The international unit for measuring frequency, equivalent to the older
unit of cycles per second. One megahertz (MHz) is one million hertz. One
gigahertz (GHz) is one billion hertz. The standard US electrical power
frequency is 60 Hz, the AM broadcast radio frequency band is 535 - 1605
kHz, the FM broadcast radio frequency band is 88 -108 MHz, and wireless
802.11b LANs operate at 2.4 GHz.
IEEE: Institute of Electrical and Electronics Engineers, New York,
www.ieee.org. A membership organization that includes engineers, scientists,
and students in electronics and allied fields. It has more than 300,000
members and is involved with setting standards for computers and communications.
IEEE 802.11: IEEE 802.xx is a set of specifications for LANs from The
Institute of Electrical and Electronic Engineers (IEEE). Most wired networks
conform to 802.3, the specification for CSMA/CD based Ethernet networks
or 802.5, the specification for token ring networks. 802.11 defines the
standard for wireless LANs encompassing three incompatible (non-interoperable)
technologies: Frequency Hopping Spread Spectrum (FHSS), Direct Sequence
Spread Spectrum (DSSS), and Infrared. WECA’s focus is on 802.11b, an 11
Mbps high rate DSSS standard for wireless networks.
Infrastructure Mode:
A client setting providing connectivity to an AP. As compared to Ad-Hoc
Mode where PCs communicate directly with each other, clients set in Infrastructure
Mode all pass data through a central AP. The AP not only mediates wireless
network traffic in the immediate neighborhood, but also provides communication
with the wired network. See AD-Hoc and AP.
IP:
The Internet Protocol (IP) is a method or protocol by which data is sent
from one computer to another on a network, i.e. the Internet. Each computer
on the Internet has at least one address that uniquely identifies it from
all other computers on the Internet. When you send or receive data (for
example, an e-mail note or a Web page), the message gets divided into
little chunks called packets. Each of these packets contains both the
sender's Internet address and the receiver's address. Any packet is sent
first to a gateway computer that understands a small part of the Internet.
The gateway computer reads the destination address and forwards the packet
to an adjacent gateway that in turn reads the destination address and
so forth across the Internet until one gateway recognizes the packet as
belonging to a computer within its immediate neighborhood or domain. That
gateway then forwards the packet directly to the computer whose address
is specified. Because the data is divided into a number of packets, each
packet can, if necessary, be sent by a different route across the Internet.
A packet is treated as an independent unit of data so packets can arrive
at their destination in a different order than they were sent in. Another
protocol, the Transmission Control Protocol, (TCP) then reassembles the
packets in the right order.
IP Address:
An IP address is a 32-bit number that identifies each sender or receiver
of information that is sent across the Internet. An IP address has two
parts: the identifier of a particular network on the Internet and an identifier
of the particular device (which can be a server or a workstation) within
that network.
ISA (or PCI):
A local bus standard for connecting peripherals to a personal computer.
Within a computer, the bus is the transmission path on which signals and
data transfers occur between the CPU, system memory, and attached devices
such as a network card, sound card, or CD-ROM drive.
ISO Network Model:
The International Standards Organization (ISO) has developed a network
model that consists of seven different levels, or layers. By standardizing
these layers, and the interfaces in between, different portions of a given
protocol can be modified or changed as technologies advance, or systems
requirements are altered. The seven layers are:
Physical
Data Link
Network
Transport
Session
Presentation
Application
The IEEE 802.11 Standard encompasses the physical layer (PHY) and the
lower portion of the data link layer. The lower portion of the data link
layer is often referred to as the Medium Access Controller (MAC) sublayer.
ISP (Internet Service Provider):
An organization that provides access to the Internet. Small ISPs provide
service via modem and ISDN while the larger ones also offer private line
hookups (T1, fractional T1, etc.). The major online services such as America
Online provide Internet access but are still known as "online services",
not ISPs. They offer the members only content, forums and services in
addition to Internet access.
LAN (Local Area Network):
A communications network that serves users within a defined geographical
area. The benefits include the sharing of Internet access, files and equipment
like printers and storage devices. Special network cabling (10BaseT) is
often used to connect the PCs together. Wireless LANs use wireless communications,
in a home or office, to network all PCs together so there is no need to
run an extra set of cables.
MAC (Medium Access Control):
In a WLAN network card, the MAC is radio controller protocol. It corresponds
to the ISO Network Model's level 2 Data Link layer. The IEEE 802.11 standard
specifies the MAC protocol for medium sharing, packets formats and addressing,
and error detection.
NAT (Network Address Translation):
The translation of an Internet Protocol address (IP address) used within
one network to a different IP address known within another network. One
network is designated the internal network and the other is the external.
The internal network then appears as one entity to the outside world.
In the case of wireless LANs with an outside Internet connection, the
NAT capability of Internet sharing software allows the sharing of one
Internet connection among all the wireless PCs connected.
PCI (or ISA):
A local bus standard for connecting peripherals to a personal computer.
Within a computer, the bus is the transmission path on which signals and
data transfers occur between the CPU, system memory, and attached devices
such as a network card, sound card, or CD-ROM drive.
PHY (Physical Layer):
The PHY is the lowest layer within the OSI Network Model. It deals primarily
with transmission of the raw bit stream over the PHYsical transport medium.
In the case of wireless LANs, the transport medium is free space. The
PHY defines parameters such as data rates, modulation method, signaling
parameters, transmitter/receiver synchronization, etc. Within an actual
radio implementation, the PHY corresponds to the radio front end and baseband
signal processing sections.
Roaming:
Moving seamlessly from one AP coverage area to another with no loss in
connectivity.
TCP (Transmission Control Protocol):
A protocol used along with the Internet Protocol (IP) to send data in
the form of individual units (called packets) between computers over the
Internet. While IP takes care of handling the actual delivery of the data,
TCP takes care of keeping track of the packets that a message is divided
into for efficient routing through the Internet. For example, when a web
page is downloaded from a web server, the TCP program layer in that server
divides the file into packets, numbers the packets, and then forwards
them individually to the IP program layer. Although each packet has the
same destination IP address, it may get routed differently through the
network. At the other end, TCP reassembles the individual packets and
waits until they have all arrived to forward them as a single file.
WEP (Wired Equivalent Privacy):
WEP data encryption is defined by the 802.11 standard to prevent (i) access
to the network by "intruders" using similar wireless LAN equipment and
(ii) capture of wireless LAN traffic through eavesdropping. WEP allows
the administrator to define a set of respective "Keys" for each wireless
network user based on a "Key String" passed through the WEP encryption
algorithm. Access is denied by anyone who does not have an assigned key.
WAN (Wide Area Network):
A wide area network connects local area networks together. Typical WAN
interfaces include plain old telephone (POT) lines, digital subscriber
lines (DSL), cable, T1/T3 and ISDN, T1/T3.
Quellen: Siemens |
