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Infrared. Infrared is the type of signal used over most fiber optic links but without the fiber media. These devices can achieve speeds of 16M bits. Products available include those specifically designed for a Token Ring environment with multiple-access units. This technology is effective in environments with an unobstructed line of site.

Exhibit 2.Advantages of Fiber Optic, Microwave, and Infrared Technologies
Option 1: Fiber Optic Option 2: Microwave Option 3: Infrared

Impervious to electrical noise and interference typically present in all office environments Low signal attenuation Freedom from government regulation, no licensing or usage fees
Systems using fiber are immune to RFI Portability of equipment, owned by the organization Portability of equipment, owned by the organization
Fiber optic poses no risk of carrying lightening charges to computer equipment Cost-effective for line-of-sight connection and when frequency bank congestion is low, this is cost-effective Ease of interconnecting additional locations
Fiber is conducive to a Token Ring environment Conducive to a Token Ring environment Immunity to radio interference
Rapid installation Reasonable installation time Reasonable installation time
High data security Signal scrambling is available through some vendors Security of the data
Upwardly scalable

Microwave. Microwave technology offers speed for transmission to 6.7M bits at a range of 130 feet and supports Ethernet. This technology has the benefit of providing ownership of materials, allowing lower costs on future relocations.

Eliminating Inappropriate Connectivity Technologies

Two of the technologies described in the previous sections were eliminated from any in-depth consideration. Twisted-pair cables were dismissed as an option because the preliminary review indicated a lack of reliability at this project’s distance — 100 feet. Twisted-pair cables also have limitations in handling the anticipated data traffic.

Spread spectrum UHF was also eliminated. Even though spread spectrum UI-IF is a secure connectivity option, it is limited in speed and best suited for small LANs. Consideration of this application to future, smaller-scale projects was recommended.

The three options given serious consideration are discussed in the following sections. Exhibits 2 and 3 summarize the advantages and disadvantages of each technology.

THE FIRST OPTION: FIBER OPTICS

Fiber optics is a communications media linking two electronic circuits by a strand of glass. It is lightweight and small, making it more attractive for projects in which space is at a premium. A graded index fiber performs best, because of its ability to carry multiple signals, with the least amount of signal loss, due to dispersion. Wide bandwidth, low signal loss, and electromagnetic immunity are the three most outstanding features of fiber optics.

Exhibit 3. Disadvantages of Fiber Optic, Microwave, and Infrared Technologies
Option 1: Fiber Optic Option 2: Microwave Option 3: Infrared

Additional repeaters are needed to boost the signals for long distances The capacity of 6.7M bits is less than the 16M-bit needed at its peak times Atmospheric conditions affect reliable data transmission
Fiber cable runs cannot be subjected to sharp turns Outside installation support required and no existing training available High up-front equipment investment and installation support
Cable terminations and splices must be specially prepared Signal or transmission unreliability during excessive rains Potential safety issue for retina damage caused by looking directly into the beam
The materials belong to the property Potential delay of licensing from the FCC, possible installation delay

Fiber Optic Data Transmission

Fiber optic systems transmit data as a series of light pulses, generated either by light- emitting diodes (LED) or lasers. The bit error rates (BERs) for fiber optic cabling are as much as 10,000 times lower than standard electrical media. The connections are further simplified by the absence of ground loops, crosstalk, ringing, and echoing.

Light propagation through fiber depends principally on three factors, including the composition, size, and light injected into the fiber. Transmitting sources commonly use LED in place of laser. With a longer lifetime than a laser light, LED is easier to use and maintain. A LED source has a higher and broader output pattern but is not capable of single-mode compatibility. The transmitter output power is coupled with the diameter of fiber, so that power increases with core diameter.

Detectors perform the opposite function from the source by converting optical energy to electrical energy. The photo diode produces current in response to incident light. Detectors are typically packaged in the same receptacles as sources. Receiver sensitivity specifies the weakest optical signal it will receive. This is affected by the amount of noise, or signal clarity, during signal receipt as measured by bit error rate (BER) or the signal-to-noise ratio (SNR).

Fiber Optic Cabling

Fiber optic cable is available in either single mode or multimode. Single mode has an aperture of about nine microns, has a low attenuation rate, and is ideally suited for long-distance networks. Multimode is available at apertures from 50 to 100 microns and has a higher attenuation rate, because signals enter at an angle and bounce off the fiber walls as they travel. This allows for use of multiple paths, making it best suited for short-distance applications. Fiber cable comes in simplex (containing one fiber), duplex (containing a sending and receiving fiber), or hybrid, in which duplex is combined with twisted pair.

A network requires only two strands of fiber; however, a multiple strand cable is often used for backup reliability for transmission. The fiber diameter is used for this type of connection is 62.5 m and has a standard cladding diameter of 125 mm. This combination offers high speed, low attenuation (3.75 dB/km), and a high bandwidth of 1,000 MHz/km at 1,300 nm.

Fiber optic cabling is versatile, with the ability to serve as a backbone, front-end, and back end of LAN networks. Both Ethernet and Token Ring network configurations are adaptable to fiber optic cabling in place of standard copper wiring. The cost of this media typically makes it best suited to campus, building, and data center network environments. Exhibit 4 displays the potential connection configuration considered for this project.

Advantages

Fiber optic connections offer a wide variety of advantages over other hardwire and wireless options. Fiber:

  Transmits data as a series of light pulses, making it impervious to electrical noise and interference typically present in all office environments.
  Is immune to radio frequency interference (RH).
  Does not conduct electricity, thus protecting computer equipment from lightning charges.
  Is a highly secure data transmission medium, because it does not radiate energy, and tapping data from it is extremely difficult.
  Is conducive to an Ethernet or Token Ring environment, as with most hardwire installations.
  Is upwardly scalable.

In addition, the installation of fiber is rapid.

Disadvantages

The disadvantages of this technology include:

  Additional repeaters are needed to boost the signals over long distances, which incurs costs.
  Fiber cable runs cannot be subjected to sharp turns.
  Cable terminations and splices must be specially prepared.
  Materials cannot be removed once they are installed.


Exhibit 4.  Fiber Optic Cable Run.


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