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Networking Fundamentals
a 56 k modem, could be used to prevent jitter in the transmission of the video. But
this can only be used in one direction. Two-way transmissions in real time could
not take advantage of buffering to eliminate jitter. Delays of 250 milliseconds (ms)
or less are tolerable for live telephone conversations and low-resolution graphics.
Delays above 250 milliseconds (ms) are generally unacceptable.
Infrared Transmission and Networking
Infrared transmission is used in point-to-point communications, which
are also known as direct line of sight. Direct line of sight means that both devices
are in direct alignment with each other and that there are no objects between
the two devices. The infrared light beam is positioned to aim directly at the
receiving device. Each device must be oriented in a position that aims toward the
other device. This is one of the main limitations to using infrared in networking
applications.
Infrared is typically used for point-to-point communications between
two devices such as a personal digital assistant and a desktop computer.
Infrared point-to-point communications can also be used in place of radio wave
communications where there might be excessive interference, such as in factory
or manufacturing settings.
Advantages and Disadvantages of Wireless
Technology
Wireless technology can be cost-effective as compared with cable-based
network media when spanning long distances such as continents or oceans.
Spanning across a city, a business district, or across a college campus can be
diffi cult and expensive with copper-core cable or fi ber-optic cable. The installation
of landlines are not only expensive, they can cause major disruption while digging
up streets and parking lots for installation. When installing a temporary network,
wireless technology can be much more cost-effective than remodeling a building
to accommodate wiring. Wireless technology is most appropriate for mobile
devices such as palmtops, communicators, personal digital assistants, and laptops.
Handheld scanners used to scan bar codes on product packages also use wireless
technology to transmit data to a computer or cash register system.
Certain wireless technologies are also affected to various degrees by
atmospheric conditions such as rain, lightning, fog, and sunspots. The greatest
disadvantage or concern for wireless technology is security. Network signals
are transmitted in the open air and are capable of being picked up by an
unauthorized receiver. Of course, data transmission may be encrypted for
security, but even the best security can sometimes be compromised.
Wireless Security
One major concern of wireless networks is security. Network infrastructures
designed to use cable are inherently more secure than wireless networks.
Cable can be installed so that it is physically secured. Cables can be installed
inside walls, pipes, and locked server rooms. Because cables can be physically
secured, cabled networks are considered more secure than wireless networks.
Unauthorized persons cannot readily connect physically to a private, cabled
network system. Wireless networks, on the other hand, transmit data through