Fiber Optic Networks
In the telcos, singlemode fiber
is used to connect long distance switches, central offices and
SLCs (subscriber loop carriers, small switches in pedestals in
subdivisions or office parks or in the basement of a larger building).
Practically every telco's network is now fiber optics except
the connection to the home. Fiber to the home (FTTH) is now cost
effective - especially since most homes want the high speed services
that would justify fiber optics. Look for FTTH first in new home
CATV companies "overbuild" with fiber. They lash fiber
cable onto the aerial "hardline" coax used for the
rest of the network or pull it in the same conduit underground.
The fiber allows them to break their network into smaller service
areas that prevent large numbers of customers from being affected
in an outage, making for better service and customer relations.
The fiber also gives them a return path which they use for Internet
and telephone connections, increasing their revenue potential.
LANs (local area networks) use fiber optics primarily in the
backbone but increasingly to the desk. The LAN backbone often
needs longer distance than copper cable (Cat 5/5e/6) can provide
and of course, the fiber offers higher bandwidth for future expansion.
Most large corporate LANs use fiber backbones with copper wire
to the desktop. Fiber to the desk can be cost effective if properly
Lots of other networks use fiber. CCTV is often on fiber for
it's distance capability. Industrial plants use lots of fiber
or distance and noise immunity. Utilities use it for network
management, liking its immunity to noise also. The military uses
it because it's hard to tap or jam. Airplanes use it for that
reason too, but also like the lighter weight of fiber.
Designing Cable Networks
I guess this is too big a topic for a overview! But we'll pass
along some hints to make life easier. First and foremost, visit
the work site and check it out thoroughly. Know the "standards"
but use common sense in designing the installation. Don't cut
corners which may affect performance or reliability. Consider
what are the possible problems and work around or prevent them.
There ain't no substitute for common sense here!
Fiber's extra distance capability makes it possible to do things
not possible with copper wire. For example, you can install all
the electronics for a network in one communications closet for
a building and run straight to the desktop with fiber. With copper,
you can only go about 90 meters (less than 300 feet), so you
need to keep the electronics close to the desk. With fiber, you
only need passive patch panels locally to allow for moves. Upgrades
are easy, since the fiber is only loafing at today's network
Is Copper Really Cheaper Than
When it comes to costs, fiber optics is always assumed to be
much more expensive than copper cabling. Whatever you look at
- cable, terminations or networking electronics - fiber costs
more, although as copper gets faster (e.g. Cat 6) it gets more
expensive, almost as much as fiber. So isn't it obvious that
fiber networks are more expensive than copper? Maybe not! There
is more to consider in making the decision.
The TIA Fiber Optic LAN Section
(FOLS) has a cost model
that allows calculation of the relative costs of fiber and copper
which can be used to compare options for your own network.
Why Use Fiber?
If fiber is more expensive, why have all the telephone long distance
and metropolitan networks been converted to fiber - and they are
now starting on fiber to the home? And why are all the CATV systems
converting to fiber too? Are their networks that different? Is there
something they know we don't?
Telcos use fiber to connect all their
central offices and long distance switches because it has thousands of
times the bandwidth of copper wire and can carry signals hundreds of
times further before needing a repeater. FTTH allows offering new
services that require more bandwidth than copper wires and reduces
maintenance. The CATV companies use fiber because it give them greater
reliability and the opportunity to offer new services, like phone
service and Internet connections.
Both telcos and CATV operators use fiber for economic reasons,
but their cost justification requires adopting new network architectures
to take advantage of fiber's strengths. A properly designed premises
cabling network can also be less expensive when done in fiber
instead of copper. There are several good examples of fiber being
less expensive, so lets examine them.
In an industrial environment, electromagnetic interference (EMI)
is often a big problem. Motors, relays, welders and other industrial
equipment generate a tremendous amount of electrical noise that
can cause major problems with copper cabling, especially unshielded
cable like Cat 5. In order to run copper cable in an industrial
environment, it is often necessary to pull it through conduit
to provide adequate shielding.
With fiber optics, you have complete immunity to EMI. You only
need to choose a cable type that is rugged enough for the installation,
with breakout cable being a good choice for it's heavy-duty construction.
The fiber optic cable can be installed easily from point to point,
passing right next to major sources of EMI with no effect. Conversion
from copper networks is easy with media converters, gadgets that
convert most types of systems to fiber optics. Even with the
cost of the media converters, the fiber optic network will be
less than copper run in conduit.
Long Cable Runs
Most networks are designed around structured cabling installed
per EIA/TIA 568 standards. This standard calls for 90 meters
(295 feet) of permanently installed unshielded twisted pair (UTP)
cable and 10 meters (33 feet) of patchcords. But suppose you
need to connect two buildings or more? The distance often exceeds
the 90 meters by the time you include the runs between the buildings
plus what you need inside each building.
By the time you buy special aerial or underground waterproof
copper cable and repeaters, you will usually spend more than
if you bought some outside plant fiber optic cable and a couple
of inexpensive media converters. It's guaranteed cheaper if you
go more than two links (180 meters.)
Centralized Fiber LANs
When most contractors and end users look at fiber optics versus
Cat 5e cabling for a LAN, they compare the same old copper LAN
with fiber directly replacing the copper links. The fiber optic
cable is a bit more expensive than Cat 5e and terminations are
a little more too, but the big difference is the electronics
which are $200 or more per link extra for fiber.
However, the real difference comes if you use a centralized fiber
optic network - shown on the right of the diagram above. Since
fiber does not have the 90 meter distance limitation of UTP cable,
you can place all electronics in one location in or near the
computer room. The telecom closet is only used for passive connection
of backbone fiber optic cables, so no power, UPS, ground or air
conditioning is needed. These auxiliary services, necessary with
Cat 5 hubs, cost a tremendous amount of money in each closet.
In addition, having all the fiber optic hubs in one location
means better utilization of the hardware, with fewer unused ports.
Since ports in modular hubs must be added in modules of 8 or
16, it's not uncommon with a hub in a telecom closet to have
many of the ports in a module empty . With a centralized fiber
system, you can add modules more efficiently as you are supporting
many more desktop locations but need never have more than a one
module with open ports.
High Speed Networking
It was over a year after Gigabit Ethernet (GbE) became available
on fiber optics that it finally become available on Cat 5e. It
took another couple of years before GbE on copper became significantly
less expensive. In order to get GbE to work over Cat 5e, the
electronics must be very complicated, and consequently as expensive
as fiber. A newer version is in the wings, awaiting a Cat 6 standard,
but that means the version running over Cat 5e will be obsolete
before it even gets started! Finally, we went to a major distributor's
seminar on advanced cabling recently and the copper marketing
guy told us to go fiber for GbE.
So when it comes to costs, looking at the cabling component costs
may not be a good way to analyze total network costs. Consider
the total system and you may find fiber looks a lot more attractive.