Page 38 - DCAP207_NETWORKS_DCAP406_COMPUTER_NETWORKS

Unit 3: Physical Layer

space often is at a premium. The physical dimensions of airwave systems also must be Notes
considered, as the size and weight of the reflective dish and mounting system (e.g., bracket
and tower) may require support.
Cost and ease of Installation: Cost issues abound in the selection of an appropriate
transmission medium. Such issues include the cost of acquisition, deployment, operation,
and maintenance (O&M), and upgrade or replacement. Without a lengthy discussion of
each cost issue, it is particularly noteworthy to compare the costs of deployment of wired
versus wireless media.
Wired transmission systems require a right-of-way and this should be secured. Wired
transmission involves a cost component in the form infrastructure. The infrastructure
includes digging of trenches and boring of holes so that cable can be pulled and poles may
be mounted. In addition, amplifiers or repeaters may be placed. Such costs are not trivial.
Unlike wired system, wireless systems require secured right-of-way and antennae. It may
be inferred that the deployment of wired systems certainly speak of a set of cost issues that
often can be more problematic.
Selection criteria: When choosing the most effective transmission media, consider the
above mentioned transmission characteristics which are listed below:
Bandwidth/Transmission rate
Distances

Propagation delay
Security
Resistance to environmental conditions
Physical dimensions

Cost and ease of installation
Self Assessment

Fill in the blanks:

1. ………………………………………………. can be broadly categorized into guided and
unguided media.
2. The actual range of frequencies supporting a given communication is known as a ............

3. In general, the higher the ………………….., the more will be the data transmission rate or
throughput.
4. ……………………………………………… refers to the length of time required for a signal
to travel from transmitter to receiver across a transmission system.
5. Bandwidth may be defined as the range of ………………………………………..assigned to
a channel.

3.2 Bounded Media

Bounded media or wired transmission systems employ physical media, which are tangible.
Also known as conducted systems, wired media generally employ a metallic or glass conductor
which serves to conduct, some form of electromagnetic energy. For example, twisted pair and
coaxial cable systems conduct electrical energy, employing a copper medium. Fibre optic systems

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