Fiber Optics and Premises Cabling
Fiber Optic Architecture For Local Area Networks (LANs)It’s
fairly obvious that fiber optics is not copper wiring. The advantages
of fiber include the capability of going longer distances at higher
speeds, plus immunity to electromagnetic radiation. These advantages
overcame fiber’s disadvantage in cost to make it the cabling of choice
for telcom and CATV. While fiber is still primarily limited to
LAN backbones in the premises cabling market, new methods and components
are increasing its acceptance.
From
the beginning, the EIA/TIA committees wrote the “568” standards around
copper wiring. There was no logical reason to limit fiber to the
architecture of UTP copper. While copper was technically limited to 100
meter links, fiber could go 2,000 meters or more at 100 Mb/s. But the
architecture of 568 was written around copper, with a backbone cable to
a telecom closet connecting the desktop over a horizontal cable of no
more than 100 meters. As LAN speeds continued rising to
gigabits/second, fiber became the media of choice for backbones,
allowing easy upgrades and more flexibility in placing telecom rooms,
as they became known, instead of "closets."
Several years ago,
fiber’s capabilities were recognized in the TIA-568 standard with the
addition of a centralized fiber architecture standard. The standard
covered a network architecture that would place fiber hubs in the
computer room and run backbone fiber to the telecom room, then through
passive interconnects to the desktop. By allowing a direct to the
desktop connection, there was no need for electronics in the telecom
room. This meant that a data ground, conditioned, uninterruptable
power, and air conditioning were also not needed, greatly reducing the
cost to the end user and making fiber cost effective compared to
copper.
The copper people learned a lesson from fiber and
created zone cabling. Zone cabling adds an additional consolidation
point near desktops. Rather than the usual run of up to 90 meters of
permanently-installed horizontal cabling using a single cable for every
desktop, zone cabling uses a backbone cable from the telecom closet to
the consolidation point, then short individual cables to the desktop.
Zone
cabling creates a “mini telecom closet” near the user. It’s a terrific
solution for modular furniture designs that include pathways for
cables. When the offices move, the furniture can be unplugged and moved
but the wiring from the telecom closet to the consolidation point
remains for future use. The modular furniture can be moved to another
point where it again connects to a local consolidation point.
Another
useful gadget is the MUTOA or "multi-user telecom outlet assembly." It
is a patch panel or box with up to 12 connections that can be installed
near a number of users who make their connections to that instead of a
wall outlet. With proper design, it can not only simplify installation,
but it can make MACs (moves, adds and changes) much easier.
There
can be a big advantage in installation, where only one cable is pulled
to an area, then shorter cables are used to connect to the desktop.
This works for fiber optics and multi-pair telephone cabling, but may
not be possible for all copper data cabling. For example, one can buy
25 pair Cat 5E cable, but not Cat 6, so if the user decides to install
Cat 6, the cable runs to the zone box must be individual Cat 6 cables.
Fiber
optics and zone cabling work well together. Using multifiber cables, a
single cable can connect multiple desktops to a backbone cable with
minimal bulk and weight, often a big problem in offices with many
desktop connections. Overhead cable trays can become filled with many
Cat 5E or Cat 6 cables, but one small, lightweight fiber cable can
connect dozens or even hundreds of desktops.
Zone cabling works well with prefabricated fiber optic cable systems
also. Cables can be factory terminated and the connectors enclosed in a
protective boot for pulling. After the cable is pulled and secured, the
boot is removed and connected to the zone box or MUTOA, and the cable
is ready for use.
These prefabricated
cable assemblies offer several advantages. They are faster to install
and have no yield problems on the connectors since every one is factory
made and tested. The total installed cost of the components is often
less than field termination, but the price to the customer is the same,
so they can be more profitable for the contractor. As a downside, they
do require more care in installation to prevent damage to the
connectors.
End users choose zone cabling for fiber to the
desk applications because it reduces cable clutter and saves them
money. It is not hard to design such a network if you know the basic
layout and choose cabling hardware early in the process. Cable
installation is easy since fewer cables are required but may require
additional terminations at the zone boxes or MUTOAs. Like all
installations, careful planning will yield an easier, neater
installation.
Is Wireless Replacing Cable To The Desktop?
For
LAN applications, it appears that the choice of copper vs. fiber to the
desktop may be neither. While these two have been trading claims over
cost, technology and power, WiFi wireless networks have been developed
to provide high quality connections at speeds that are more than
adequate for most users and security issues have been addressed.
The
move to wireless connectivity has happened because most corporate users
now prefer laptops (with built-in WiFi) to desktop computers for
mobility. Many people also own portable mobile devices like smart
phones, iPhones and Blackberries with wireless access that are becoming
almost as powerful as a laptop.
Within the enterprise LAN, the
backbone is primarily fiber, with new installations mostly using OM3
laser-optimized 50/125 variety capable of being upgraded from today’s 1
to 10 gigabits per second to 40 or even 100 in the future. The
remaining desktop computer users will still get Cat 5e or Cat 6 to the
desktop since it’s cheaper.
The new generation of higher
bandwidth wireless requires more access points which have traditionally
been connected over copper, and recently have been powered over the
same copper cables also. But there seems to be some question about
whether adequate power for these new wireless access points can be
carried over the same copper cables that must provide Gigabit Ethernet
connectivity. Fiber may prove to be a better choice here too.
Data Centers
Data
centers are comprised of many computers acting as servers, pulling data
from storage disks and sending it to routers for transmission over the
Internet. Because of the massive amounts of data served, data center
links use the highest speeds available, currently 1 gigabit or 10G
Ethernet or Fibre Channel at 1, 2, 4, 8 or 10 Gb/s.
At 1 Gb/s
the choice for connections are fiber or UTP copper, with copper
probably being more popular. As data centers migrate to links with
speeds above 1 Gb/s, UTP cabling must be upgraded to Cat 6A (augmented
Cat 6) which is expensive, much larger than Cat 5e or Cat 6, and
requires transceivers that consume 4-8 times as much power as
fiber transceivers, a big problem in data centers where power
consumption - and the heat generated - cause problems. Other choices
are coax copper for short links or fiber for any length of link. Most
data centers use those two choices, with the fiber being high bandwidth
laser-optimized 50/125 OM3 fiber.
More on Data Centers.
The FOA Reference Guide on Premises Cabling.
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