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EYE ON FIBER
Knowledge Required For Designing The Fiber Optic
Network
Subtleties, Specifications, Process,
And Cost Estimates
Introduction
The simple way
to design a fiber optic network is to reference TIA/EIA-568-B. While such a
reference works, this approach does not allow the designer to achieve the
highly desirable goals of maximum ROI, minimum total installed cost, optimum
design and maximum reliability. To design a high ROI, cost effective, optimum
and reliable fiber network, the designer needs to understand the basics of
fiber optic networks, the design process and the cost impact of design
decisions.
The Basics
And Important Subtleties
The basics
include the language of fiber optic components, the optional performance
numbers of those components, and the performance numbers that result from use
of TIA/EIA-568-B. While the performance numbers of TIA/EIA-568-B are
reasonable, their use rarely results in an optimum network design.
Heresy you say?
Not at all. All standards are politically negotiated compromises.[1] As such they can never be technical or
cost optimal solutions. To achieve an optimum network design, the designer must
know the benefits and drawbacks inherent in TIA/EIA-568-B and the optional
specifications available. Two examples will help.
Example 1: fiber
characteristics such as core offset, cladding non-circularity, core diameter
tolerance, and cladding diameter tolerance are critical to achieving
sufficiently low connector loss. These characteristics are set by TIA/EIA-568-B
through reference to two international cable standards, ICEA S-83-596-2001, for
premises distribution cable and ANSI/ICEA S-87-640-1999, for outdoor cable. As
international standards, the values of these four characteristics have been
established through political compromise between international fiber
manufacturers. Did you know that these characteristics of US-made fiber and
much of the overseas-made fiber are superior to those in these two standards?
Without knowledge of these characteristics, the designer can, through
blindness, allow reduced reliability and increased connector loss into his
design.
Example 2: blind
adherence to TIA/EIA-568-B fiber performance values can result in less than
ideal life cycle. Use of laser optimized, 50 µm fiber can result in increased
life cycle and reduced life cycle cost. Again, without such knowledge of
options, the designer can create a less than optimum design.
These two
examples are of the subtlety of the design process. Often, I find that highly
experienced network designers benefit from knowledge of the many subtleties in
the fiber optic network design process.
In addition, subtle knowledge of potential fiber specifications allows
designers to create networks that would be impossible with straight
TIA/EIA-568-B specifications.
The Nine-Step
Design Process
The process of
designing a fiber optic network can be organized in many ways. I have chosen to
organize it as a series of nine steps (Table 1).
Table 1: The Nine-Step Design Process
Define basic
requirements
Map the
network
Make the
multimode/ singlemode decision
Determine
optical requirements
Determine
non-optical requirements
Future proof
the network
Identify
potential components
Choose
components
Determine
acceptance requirements
Each of these steps
is a series of questions. Each question has multiple answers possible,
depending on the specific network to be designed. For instance, a building
riser network will have answers different from those of a process control
network in a steel mill.
Of these eight
steps, the second and ninth have the most common difficulties.
Step 2: Map
the Network
Step two
requires the designer to map the network. On this map, he indicates the
installation and environmental conditions. It is not unusual for the designer to
overlook important environmental conditions and specify the cable performance
inadequately.
For example, a
building-to-building network in a hospital facility may have a link through a
tunnel. As is common in medical facilities, this tunnel may have steam pipes.
If the steam pipes, commonly located at the top of the tunnel, create a
temperature above the maximum operating temperature range of the cable, as
specified by TIA/EIA-568-B through its reference to ICEA S-83-596-2001, the end
to end power loss will be higher than expected. More importantly, the cable
materials may experience degradation that can result in cable failure years
after the installation. In this case, the reference to TIA/EIA-568-B will not
provide the desired reliability.
Step 9: Determine
Acceptance Requirements
Step 9 requires
the designer to specify the maximum power loss that will be acceptable at the
completion of the installation. While TIA/EIA-568-B allows this power loss to
be at the maximum power loss values of cables and connectors, this maximum loss
will not be reached unless the installer makes mistakes. Such mistakes result
in reduced reliability. In other words, setting maximum power loss values with
the maximum loss values from TIA/EIA-568-B can result in reduced reliability.
The question becomes: how does the designer calculate acceptance values. This
subject requires more space than we have in this article. In FiberPro
5, we address possible
strategies and a recommended strategy.
Cost Analysis
Essential To High ROI And Minimum Cost
No design should
be finalized until the designer performs at least two cost analyses. In many
cases, the designer will perform four or five cost analyses to determine the
combination of components and installation methods that result in either the
lowest total installed cost and/or the highest ROI.
Cast In
Concrete Rule 1: Choose Products With Lowest Total Installed Cost
Corollary to
Rule 1: Never Choose Products With Lowest Cost
There is a tendency
to choose products based on product cost. This tendency can, and often does,
result in a hidden increase in cost. Four examples will help.
Example 1: some
connector installation methods offer increased installation rate (Figure 1).
Such methods tend to require connectors that have costs higher than those of
connectors with reduced installation rates. If the reduction in labor cost is
more than the premium paid for the connector method with the increased
installation rate, the higher cost connector will result in a reduced total
installed cost.
Does this type
of cost comparison sounds simple? It is. Reality is never this simple. In any
installation, there is factor I call labor utilization. Utilization (Figure 2)
is the ratio of time spent in the specific activity to the total time required
for that activity. If we consider connector installation, there is time for
travel to the installation site, time for setting up the installation
equipment, time for cleaning up and packing the installation equipment, and the
time for installing the connectors. Obviously the labor utilization will be
less than 100 %.
In addition,
this utilization will vary from situation to situation. For example, an
installer who installs four connectors at a location will experience a lower
utilization than an installer who installs 48 connectors at a location. This
subtle factor of labor utilization can influence the connector installation
method, favoring one method in one design and a different method in a second
design. The designer needs to understand and include consideration of
utilization in both his total cost estimate and in his choice of connector
installation method. Without such consideration and multiple cost analyses, the
designer can underestimate the total cost of the network and unknowingly choose
a design or product a hidden excessive cost.
Example 2: some
building-to-building networks require termination of cables at a location other
than the basement entry location. With this requirement, an indoor cable will
connect to an outdoor cable. This connection has a cost that can be
$20-$40/fiber. An alternative configuration can use an indoor-outdoor cable.
Such a cable will eliminate the connection cost but can require an
indoor-outdoor cable with a cost higher than the cost of the indoor and outdoor
cables. In this situation, the designer will perform two total installed cost
analyses to determine the alternative with the lowest total installed cost. In
one case, a designer paid $700 more for the indoor-outdoor cable. This designer
saved $7200 in connection costs.
Example 3: a
designer chose break out cable without any cost analysis. This blind choice
resulted in a total installed cost that was 50 %, and $100,000, higher than an
alternative cable choice. Without
multiple cost analyses, the designer risks a network with excessive cost and
the resultant reduced ROI.
Example 4: fiber
to the desk is commonly viewed as too expensive. Yet for new builds, many FTTD
networks have initial installed costs that are less than those of traditional
horizontal UTP, vertical riser fiber networks.
FiberPro 5
Provides The Needed Knowledge
In its three
major sections, FiberPro 5 addresses the main issues of fiber optic
network design: the basics, the design process, and cost analysis. As part of
the cost analysis section, attendees receive three complex spreadsheets[2] that allow attendees to choose the
lowest total installed cost based on the specifics of their networks. Attendees
practice what they learn through development of a comprehensive design package,
complete with fiber, cable, connector and optoelectronic specifications,
certification specifications, and cost estimates. As tools for use in this
development, attendees receive five additional computer files that can be used
as specification forms in designs performed after the program. FiberPro
5 is a four-day program
with BICSI CECs as shown in Table 2.
Table 2: CECs Available From FiberPro
5
RCDD 28
NTS 7
OSP 28
ITS Installer 12
Technician 12
BICSI Master
Instructor, Eric R. Pearson, CPC, CFOS, developed and delivers FiberPro 5. Mr.
Pearson is a 29-year veteran of fiber optic communications.
Respectfully submitted for your consideration,
Eric
R. Pearson, CPC, CFOS
President
Pearson
Technologies Inc.
For
Mr. Pearson contact information, click
here.
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