Bandwidth : commonly it is the size of the channel used by
the radio (the amount of frequency available to the system). By
extension, it can also sometimes refer to the speed of the system (the
Bit-rate : speed at which bits are transmitted over
the physical layer, also called signalling rate. Quite different from
throughput (see chapter 5.4.1).
Carrier : the base frequency used by the system. The
modulation process will generate a signal centered on the carrier, of
width equal to the bandwidth.
Carrier Sense : checking the transmission medium to assess
if it is free or if there is a transmission going on. Usually measure
of the received power. See CSMA.
CDMA (Code Division Multiple Access) : technique used
to share the same bandwidth between different channels using
codes. The code is a signature multiplexed with the signal and used to
recover it. See chapter 4.3.1.
CSMA (Carrier Sense Multiple Access) : using carrier sense
to access the medium. One of the main MAC methods, see a verbose
explanation in chapter 5.1.2.
Cell : radio neighbourhood, area where all nodes can
communicate with each other. As the range over radio is limited, the
network is split into independent cells and a cell to cell
communication is provided (via access point or internal routing).
Channel : On the radio, this is usually synonym of a
specific frequency, and by extension the communication medium. It can
also mean a stream of data between two nodes (a point to point link in
connection oriented systems).
dB (decibel) : logarithmic way to express a value. Usually
the signal strength (transmitted and received power) is expressed in
dBm (the reference is 1 mW - 0 dBm). A difference between two values
in dBm is without unit, in dB (in fact, this is a factor between the
two values). See chapter 4.6.
Ethernet : standard wired LAN protocol. Includes physical
and link layers.
Fading : variation in channel performance due to the
dynamicity of the environment, make the receive signal strength
change. See chapter 4.8.1.
FEC (Forward Error Correction) : technique used to
overcome some type of errors created by transmission on noisy
channels, by adding redundancy bits to the main data transmission. See
Frequency band : portion of the radio spectrum delimited
for a particular use. For example, most wireless LANs use the 2.4 to
2.48 GHz band. A frequency band is usually divided in channels.
Header : informations added by the protocol in front
of the payload in the packet for its own use (addresses, packet type,
sequence number, CRC...). Each protocol adds a different header, so in
a typical TCP/IP packet as transmitted, we have a MAC header, an IP
header and a TCP header, followed by the payload.
IP : see TCP/IP.
IPX : network protocol used in Netware, usually with SPX.
LAN (Local Area Network) : network on a short
distance, as opposed to WAN (typically inside a building).
Latency : measure of the performance of a network for
short requests and multimedia traffic. There is no real standard
measurement, it might be the time to send and transmit a packet, or
the time spent in the transmit queue, or the time for an answer to
come back, or a number of requests per second...
Layer : this terminology comes from the OSI
specification. It divides any communicating system into 7 layers, each
having a different functionality. Layer 1 is the physical layer, and
layer 2 is the link layer. IP could be assimilated as layer 3 (network
layer), and TCP as layer 4 (transport layer).
Link layer : This is the part of the protocol managing
the direct delivery between two devices on a specific physical layer
(coaxial bus, point to point link, radio...). This includes
packetisation and addressing. Most of this is implemented in the MAC.
MAC (Medium Access Control) : this is the part of the
radio device managing the protocol and the usage of the link. The MAC
decides when to transmit and when to receive, creates the packets
headers and filters the received packets. See chapter 5.1 for the
main examples of MAC protocols.
Medium : name to describe the mean used to transfer
information. This could be a wire (twisted pairs, coax...), an optic
fibber, the radio waves (the air), infrared light...
Modem (modulator/demodulator) : in a radio device,
this is the part converting the bits to transmit into a modulation of
the radio waves and the reverse at the reception. It does the analog
to digital conversion, the generation of the frequency, the modulation
and the amplification.
Modulation : specific way of coding information on a
radio frequency. Basically, there is amplitude modulation (AM - change
waveform strength) and frequency/phase modulation (FM - change
waveform timing), but there exist many variations and combinations
each designated by a specific acronym. See chapter 4.7.
NetBeui : network protocol used in Lan Manager.
Node : a device part of the network, source or
destination of the data. For us, a computer with a radio card in it.
Noise : any unwanted signal. Background noise,
interferences, transmissions from nodes not belonging to the
network... See chapter 4.8.
Packet : Unit of transmission over the network. The
data to be transmitted is split into packets, which are sent
individually over the network.
Protocol : specification of the interactions between
systems and the data manipulated. This describes what to do and when
(the rules), and the format of the data exchanged on the lower
Physical layer : this is the part of the device
interacting with the medium. For a radio LAN, the physical layer is
also called modem.
Radio : electromagnetic waves. By extension, a device
transmitting or receiving radio waves.
Roaming : ability to move between cells of the same
network. See chapter 5.3.2.
SNR (Signal to Noise Ratio) : difference in strength
between the signal we want to receive and the background noise (or any
unwanted signal). See chapter 4.6.4.
TCP/IP : network protocol used by Unix and
Internet. Better in some respects than NetBeui and IPX (allows
routing, for example).
TDMA (Time Division Multiple Access) : technique used
to share the same bandwidth between different channels using periodic
time slots. See chapter 5.1.1.
Throughput : measure of the performance of a network
for large data transfer (such as FTP, NFS, HTTP 1.1). This speed is
expressed in bits per seconds or a multiple.
WAN (Wide Area Network) : network on a large
scale : a town, a country or the world. Definitely not a LAN.
Wired : using a wire.
Wireless : not using a wire. For networks, it might be
radio or infrared.