Fiber U

Fiber Optic Network Design Lesson Plan No. 8: Case Studies

Note: When you finish this lesson, you may take the online exam for your Fiber U Certificate of Completion.

Objectives: From this self-study lesson you should learn:
  • How to Apply your knowledge from lessons 1-7 on a number of different case studies
  • How to choose components and calculate loss budgets
  • How to calculate a loss budget
  • How to specify tests of a completed network.

Now it is time to apply what you have learned. The case studies are descriptions of networks that are typical for fiber optic installations that will require you to choose the proper components, calculate loss budgets and make other decisions as to how the cable plants should be designed.
CFOS/D Course Case Studies
These are a series of case studies created for use as laboratory and homework exercises as part of classes preparing for the FOA CFOS/D Fiber Optic Network Design Certification. Each case study presents a scenario that is relevant to the actual work of designing a fiber optic network.

For each case study, a schematic of the network or system is given, along with some basic information on the proposed communications equipment and a series of questions on the scenario presented. Each system is described generally, assuming that the student is familiar with various types of fiber optic communications systems, including what type of equipment is required and the specifics of most communications equipment transceivers. Students should use the information provided to create a basic system design, choose components, do a loss budget analysis, create a test plan and look at some alternative scenarios. All the questions should be answered.

A reference table of typical specifications for fiber optic components and communications systems is given below for use in the exercises but most case studies will give specifications appropriate for the case study itself.


References needed are available online as well as in the FOA textbooks.

Student Assignment:
Complete the case study exercises below. You may not want to complete all of them, but should complete the ones most relevant to your work.

Note: If you are working on FOA certification, print out (PDF) your completed case studies and save along with your Fiber U Certificate of Completion for your application for certification.

Case Study No. 1: Fiber To The Home  
Case Study No. 2: Metropolitan Telecom Network  
Case Study No. 3: Long Distance Telecom Network  
Case Study No. 4: Corporate LAN Backbone  
Case Study No. 5: Campus LAN Backbone  
Case Study No. 6: Industrial Link  
Case Study No. 7: Data Center  
Case Study No. 8: CCTV Surveillance Link 
Case Study No. 9: Metropolitan Government Network  
Case Study No. 10: Optical LAN (OLAN) 

Typical Specifications

Representative component specifications for typical products on the market are included in the table below, but do not necessarily have to be used.


Component Specifications



Fiber Loss


Multimode GI @ 850 nm

3 dB/km (TIA 568: 3.5 dB/km)

Multimode GI @ 1300 nm

1 dB/km (TIA 568: 1.5 dB/km)

Singlemode at 1310 nm

0.4 dB/km (TIA 568: 1 dB/km)

Singlemode at 1550 nm

0.25 dB/km



Splice Loss

(TIA 568: 0.3 dB, all types)

Multimode, fusion

0.1 dB

Multimode, mechanical

0.3 dB

Singlemode, fusion

0.05 dB

Singlemode, mechanical

0.3 dB



Connector Loss

(TIA 568: 0.75 dB, all types)

Multimode, adhesive/polish

0.3 dB

Multimode, prepolished/splice

0.75 dB

Singlemode, adhesive/polish

0.3 dB

Singlemode, prepolished/splice

0.75 dB



Coupler  (PON)

Coupler Loss (includes typical excess loss)


4 dB










Active Device and System Specifications


Digital Transceiver Specs

Power (dBm), T=transmit, R=receive

850 nm LED (up to 10 Mb/s)

T: -15 / -25 (into 62.5 / 50 fibers)


R: -20 > -30

1300 LED (100-200 Mb/s)

T: -15 / -20 (into 62.5 / 50 fibers)


R:  -20 > -30

850 VCSEL (>1 Gb/s)

T: -3 > -10


R: 0 > -10

1310 laser  (>1 Gb/s)

T: 0


R: -10 > -20

1550 laser  (>1 Gb/s)

T: 0


R: -10 > -20

 1550 laser with fiber amplifier

T: +10 > +20


R:  -10 > -20

Video Link Specs


850 nm LED

T: -15 / -20 (into 62.5 / 50 fibers)


R: -25

1310 laser

T: 0


R: -10 > 0

1550 laser

T: 0


R: -10 > 0

 1550 laser with fiber amplifier

T: +15 > 20


R: -10 > 0


LED, Laser and receiver specifications are typical numbers for use in course case studies but do not reflect any actual product specifications.

LEDs couple about 5 dB less power into 50/125 fiber than 62.5/125 fiber, while it makes no difference for lasers.

Higher receiver power should be considered the point at which receivers are over-driven and require attenuators.

Link margin specifications for most standardized fiber optic networks are on the FOA Tech Topics Site ( It should be used as a reference for designers and for the courses. Remember supportable distances for some links at > 1 Gb/s are bandwidth limited.

Fiber U Certificate
Get a "Certificate of Completion" When You Complete The Course
After you complete the Fiber U Basic Fiber Optics online self-study course, you can now take an online exam and, when you pass the exam, get a "Certificate of Completion" for this course. You should complete all lessons including taking the quiz ("Test Your Comprehension") at the end of every lesson. When you think you are prepared, you can take an online exam for a nominal fee ($20) which will give you
a "Certificate of Completion" for this course.

If you are working on FOA certification, print out (PDF) your completed case studies from Lesson 8 and save along with your Fiber U Certificate of Completion for your application for certification.

Read more about the Fiber U Certificate of Completion program.

For more information on the FOA and its certification programs, go to the FOA page on certification.

For information on the FOA "Work to Cert" direct certification program for those with industry experience, go here.

When you finish all lessons, go here to take the Fiber U Design Certificate of Completion Exam  

Return To Fiber Optic Network Design Self Study Program Home Page


Table of Contents: The FOA Reference Guide To Fiber Optics

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