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13 Fiber Optic Communication Networks
13.13 Suppose the optical power emerging from a feeder fiber is to be distributed
among eight individual houses. Assume that they are separated by 100 m and
lie along a straight line going out from the end of the feeder fiber. One way
to distribute the power is to use a 1 × 8 star coupler and run individual fibers
to each house. Why is this preferable to the configuration where a single
fiber runs along the line to the homes and individual tap couplers in the fiber
line each extract 10% of the power from the line for each house that the line
passes?
[Answer: The star coupler will distribute an equal amount of optical power to
each house. The other configuration results in dramatically different power
levels between the first and last houses on the line.]
13.14 Because the ranging procedure in a PON has limited accuracy, a guard time is
placed between consecutive bursts from the ONTs to avoid collisions of the
independent packets, as Fig. 7.18 illustrates. Verify that a 25.6-ns guard time
consumes 16 bits at 622 Mb/s, 32 bits at 1244 Mb/s, and 64 bits at 2.488 Gb/s.
[Example, at 622 Mb/s one bit occupies a 1/(622 × 106) s = 1.6 ns time slot.
Thus 16 bits occupy 25.6 ns.]
13.15 An ONT intended for indoor installation requires a 12-V dc power supply
and consumes 15 W of electric power during normal operation. If there is
an electric power outage, the ONT disables nonessential services and now
consumes 7 W of power supplied by backup batteries. Using vendor data
sheets, select an indoor uninterruptible power supply (UPS) that satisfies
these requirements.
13.16 An ONT intended for outdoor installation requires a 12-V dc power supply
and consumes 15 W of electric power during normal operation. If there is
an electric power outage, the ONT disables nonessential services and now
consumes 7 W of power supplied by backup batteries. Using vendor data
sheets, select an outdoor uninterruptible power supply (UPS) that satisfies
these requirements. Assume the UPS must operate over temperature extremes
of −25 to +35 °C.
References
1. B.A. Forouzan, Data Communications and Networking, 5th edn. (McGraw-Hill, New York,
2013)
2. The Fiber Optic Association, The FOA Reference for Fiber Optics, www.thefoa.org/tech/ref/
OSP/jargon.html. Accessed June 2020
3. T. Anttalainen, V. Jaaskelainen, Introduction to Communication Networks (Artech House,
2015)
4. ITU-T Rec. X.210, Open Systems Interconnection Layer Service Definition Conventions (Nov.
1993)
5. R. Ramaswami, K.N. Sivarajan, G. Susaki, Optical Networks, 3rd edn. (Morgan Kaufmann,
Burlington, 2009)
6. L. Peterson, B. Davie, Computer Networks, 5th edn. (Morgan Kauffman, Burlington, 2012)
13 Fiber Optic Communication Networks
13.13 Suppose the optical power emerging from a feeder fiber is to be distributed
among eight individual houses. Assume that they are separated by 100 m and
lie along a straight line going out from the end of the feeder fiber. One way
to distribute the power is to use a 1 × 8 star coupler and run individual fibers
to each house. Why is this preferable to the configuration where a single
fiber runs along the line to the homes and individual tap couplers in the fiber
line each extract 10% of the power from the line for each house that the line
passes?
[Answer: The star coupler will distribute an equal amount of optical power to
each house. The other configuration results in dramatically different power
levels between the first and last houses on the line.]
13.14 Because the ranging procedure in a PON has limited accuracy, a guard time is
placed between consecutive bursts from the ONTs to avoid collisions of the
independent packets, as Fig. 7.18 illustrates. Verify that a 25.6-ns guard time
consumes 16 bits at 622 Mb/s, 32 bits at 1244 Mb/s, and 64 bits at 2.488 Gb/s.
[Example, at 622 Mb/s one bit occupies a 1/(622 × 106) s = 1.6 ns time slot.
Thus 16 bits occupy 25.6 ns.]
13.15 An ONT intended for indoor installation requires a 12-V dc power supply
and consumes 15 W of electric power during normal operation. If there is
an electric power outage, the ONT disables nonessential services and now
consumes 7 W of power supplied by backup batteries. Using vendor data
sheets, select an indoor uninterruptible power supply (UPS) that satisfies
these requirements.
13.16 An ONT intended for outdoor installation requires a 12-V dc power supply
and consumes 15 W of electric power during normal operation. If there is
an electric power outage, the ONT disables nonessential services and now
consumes 7 W of power supplied by backup batteries. Using vendor data
sheets, select an outdoor uninterruptible power supply (UPS) that satisfies
these requirements. Assume the UPS must operate over temperature extremes
of −25 to +35 °C.
References
1. B.A. Forouzan, Data Communications and Networking, 5th edn. (McGraw-Hill, New York,
2013)
2. The Fiber Optic Association, The FOA Reference for Fiber Optics, www.thefoa.org/tech/ref/
OSP/jargon.html. Accessed June 2020
3. T. Anttalainen, V. Jaaskelainen, Introduction to Communication Networks (Artech House,
2015)
4. ITU-T Rec. X.210, Open Systems Interconnection Layer Service Definition Conventions (Nov.
1993)
5. R. Ramaswami, K.N. Sivarajan, G. Susaki, Optical Networks, 3rd edn. (Morgan Kaufmann,
Burlington, 2009)
6. L. Peterson, B. Davie, Computer Networks, 5th edn. (Morgan Kauffman, Burlington, 2012)