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If a receiver is not tuned to the right frequency, a spread-spectrum signal looks
like background noise. There are two main alternatives, Direct Sequence
Spread Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS).
SPI (Stateful Packet Inspection) - A firewall technology that monitors the state
of the transaction so that it can verify that the destination of an inbound pack-
et matches the source of a previous outbound request. It examines not just the
headers of the packet, but also the contents, to determine more about the pack-
et than just its source and destination information. It is called "stateful" because
verifies that the stated destination computer has previously requested the cur-
rent communication. In this way, it verifies that all communications are initiat-
ed by the recipient computer and are taking place only with sources that are
known and trusted from previous interactions. In addition to being a more rig-
orous inspection, stateful packet inspection closes off ports until connection to
the specific port is requested. This allows an added layer of protection from the
threat of port scanning.
SSID (Service Set IDentifier) - A unique name shared among all points in a
wireless network. The SSID must be identical for each point in the wireless net-
work and is case-sensitive.
Static IP Address - A permanent IP address that is assigned to a node in an IP
or a TCP/IP network.
Static Routing - Forwarding data in a network via a fixed path. Static routing
cannot adjust to changing line conditions as can dynamic routing.
Subnet Mask - The method used for splitting IP networks into a series of sub-
groups, or subnets. The mask is a binary pattern that is matched up with the IP
address to turn part of the host ID address field into a field for subnets.
Switch - 1. A data switch connects computing devices to host computers,
allowing a large number of devices to share a limited number of ports. 2. A
device for making, breaking, or changing the connections in an electrical cir-
cuit.
TCP (Transmission Control Protocol) - A method (protocol) used along with
the IP (Internet Protocol) to send data in the form of message units (datagram)
between network devices over a LAN or WAN. While IP takes care of handling
the actual delivery of the data (routing), TCP takes care of keeping track of the
individual units of data (called packets) that a message is divided into for effi-
Wireless Access Point Router with 4-Port Switch
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Router - Protocol-dependent device that connects subnetworks together.
Routers are useful in breaking down a very large network into smaller subnet-
works; they introduce longer delays and typically have much lower throughput
rates than bridges.
RTS (Request To Send) - An RS-232 signal sent from the transmitting station
to the receiving station requesting permission to transmit.
Server - Any computer whose function in a network is to provide user access
to files, printing, communications, and other services.
SMTP (Simple Mail Transfer Protocol) - The standard e-mail protocol on the
Internet. It is a TCP/IP protocol that defines the message format and the mes-
sage transfer agent (MTA), which stores and forwards the mail.
SNMP (Simple Network Management Protocol) - A widely used network
monitoring and control protocol. Data is passed from SNMP agents, which are
hardware and/or software processes reporting activity in each network device
(hub, router, bridge, etc.) to the workstation console used to oversee the net-
work. The agents return information contained in a MIB (Management
Information Base), which is a data structure that defines what is obtainable
from the device and what can be controlled (turned off, on, etc.).
Software - Instructions for the computer. A series of instructions that performs
a particular task is called a "program." The two major categories of software are
"system software" and "application software." System software is made up of
control programs such as the operating system and database management sys-
tem (DBMS). Application software is any program that processes data for the
user.
A common misconception is that software is data. It is not. Software tells the
hardware how to process the data.
Spread Spectrum - Spread Spectrum technology is a wideband radio frequen-
cy technique developed by the military for use in reliable, secure, mission-crit-
ical communications systems. It is designed to trade off bandwidth efficiency
for reliability, integrity, and security. In other words, more bandwidth is con-
sumed than in the case of narrowband transmission, but the trade off produces
a signal that is, in effect, louder and thus easier to detect, provided that the
receiver knows the parameters of the spread-spectrum signal being broadcast.
Instant Wireless
®
Series
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