Glossary
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. CCK: Complementary code keying 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: Direct Sequence Spread Spectrum
and Frequency Hopping Spread Spectrum 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. 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抯
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:
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 also an RF device. 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. Mcps: Mega chips per second Msps: Mega symbols per second 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.
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