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Media installation
It is important to calculate all costs involved when designing networks.
The impact of building design and construction must be considered when
installing LAN media. Some important factors to consider include existing
heating, ventilation, and air conditioning (HVAC), water, drain, lighting, and
electrical systems. The structural materials such as drywall, concrete, wood,
and steel, as well as fire codes, must also be considered. Many walls have a
structural and a fire containment role, and cannot be punctured without taking
special steps to restore their integrity.
LANs will quickly become a
mixture of wired and wireless systems, depending on the network needs and
design constraints. In larger enterprise networks, the core and distribution
layers will continue to be wired backbone systems, typically connected by fiber
optics and UTP cables. The layer closest to the end user, the access layer,
will be the one most affected by wireless deployment.
Building-to-building Wireless Links
Building-to-building
connections are typically made using fiber optics, because of the high
available speeds and the avoidance of the ground protection measures required
with copper media. Installing fiber-optic cable between buildings is very
expensive and time consuming. Even short distances are difficult to cover due
to existing underground utilities, concrete, and other structural obstacles.
Lashed aerial installation is an alternative installation choice. WLANs have
currently become a popular choice since installation is limited to building
mounted antennas. What about building-to-building connections where distances
exceed property bounds or cabling limitations? Most businesses utilize WAN
connectivity between distant metropolitan sites. Some businesses use microwave
between distant sites. With wireless LAN bridges, buildings up to 32 km (20
miles) away can be connected at speeds up to 11 Mbps.
Typically, the
greater the distance between buildings the higher the cost of wireless LAN
installation. The standard, rubber duck antennas will not be adequate. Towers
and special high-gain antennas are required. Tower installations can be
expensive, depending on the height and construction requirements. The initial
cost may be recovered within the first year. Savings are generated from
increased productivity using greater bandwidth and discontinued monthly
leased-line fees.
Cisco wireless bridges offer many advantages over more
costly alternative connections. For example, a T-I line typically costs
approximately 400 to 1000 U.S. dollars per month. For a site with four
buildings, that could cost anywhere from 15,000 to 36,000 U.S. dollars per
year. With a wireless system, payback for the hardware costs could actually
occur in less than a year.
If a T-I line is not available or the
buildings are located on the same property, an underground cable could be put
in place. However, trenching can cost over 100 U.S. dollars for every 0.3 m (1
ft), depending upon the task. To connect three buildings located 305 m (1000
ft) apart from each other, the cost could exceed 200,000 U.S. dollars.
Microwave is a possible solution. With microwave a government license is
usually required. In the United States, this is obtained from the Federal
Communications Commission (FCC). This license serves as a registration process
that allows the license holder to take legal action against those who
interfere. The cost of the equipment is typically over 10,000 U.S. dollars per
site, which does not include the cost of installation items. Performance may be
severely degraded in the event of heavy fog, rain, or snow. Microwave also
tends to be point-to-point. Multipoint connections are usually not possible.
Regardless of whether they are wired or wireless, modern networks must
be able to handle higher bandwidth, more users, more applications, and more
mobility. Mixtures of both wired and wireless technologies are required to
provide the solutions. The network designer is responsible for providing the
most cost-effective design and solution that meets or exceeds the
organizational needs.
A site survey must be completed before deployment
decisions are made. For instance, initial plans may include a wireless
solution, but the site survey could indicate that wireless will be ineffective.
Conversely, a wired solution may be initially planned and the final survey may
prove wireless to be a better choice. Site design, preparation, and survey will
be covered in detail later in the course.
Lab Activity
Lab
Exercise: Wireless Component and Media Identification
The student will
identify the basic media characteristics of WLANs and the components of a WLAN.
Students will also describe the functions of these wireless components.
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