A glossary
of terms related to wireless network technologies
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 define 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 passes 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:
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): protocol A 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.
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.
WECA: Short for Wireless Ethernet Compatibility
Alliance, The
Wi-Fi Alliance is a nonprofit international association formed in 1999 to
certify interoperability of wireless Local Area Network products based on IEEE
802.11 specification. Currently the Wi-Fi Alliance has 202 member companies
from around the world, and 580 products have received Wi-Fi certification since
certification began in March of 2000. The
goal of the Wi-Fi Alliance's members is to enhance the user experience through
product interoperability.
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.
Wi-Fi: It's powerful. Wi-Fi networks use radio technologies called IEEE
802.11b or 802.11a to provide secure, reliable, fast wireless connectivity. A
Wi-Fi network can be used to connect computers to each other, to the Internet,
and to wired networks (which use IEEE 802.3 or Ethernet). Wi-Fi networks
operate in the unlicensed 2.4 and 5 GHz radio bands, with an 11 Mbps (802.11b)
or 54 Mbps (802.11a) data rate or with products that contain both bands (dual
band), so they can provide real-world performance similar to the basic 10BaseT
wired Ethernet networks used in many offices.
Wi-Fi
Alliance: An organization made up of leading
wireless equipment and software providers with the missions of certifying all 802.11-based
products for interoperability and promoting the term Wi-Fi as the global
brand name across all markets for any 802.11-based wireless LAN products.