Fiber optics 1-5

1. FIBER OPTIC BASICS
Part 5 - Networks

2. Fiber Optic Networks
Each application of fiber optics has unique
characteristics as a result of their
applications. Lets examine a few of them.
• Telecom
• CATV
• LAN
• Others
An overview of how fiber is used in today’s
communication networks.

3. Networks - Telecom Technology
Fiber optics has become widely used in tele-
communications because of its enormous bandwidth
and distance advantages over copper wires. The
application for fiber in telephony is simply connecting
switches over fiber optic links.

4. Networks - Telecom Technology
Commercial systems today
carry more phone
conversations over a
single pair of fibers than
could be carried over
thousands of copper pairs.
Material costs, installation
and splicing labor and
reliability are all in fiber's
favor - not to mention
space considerations. In
major cities today,
insufficient space exists in
current conduit to provide
communications needs
over copper wire.

5. Networks -
Telecom
Technology
While fiber carries over 90% of all
long distance communications and
50% of local communications, the
penetration of fiber to the curb
(FTTC) and fiber to the home (FTTH)
has been hindered by a lack of cost
effectiveness. These two final
frontiers for fiber in the phone
systems hinge on fiber becoming
less expensive and the customer
demand for high bandwidth
services impossible over current
copper telephone wires.
Telecom systems operate at bit
rates up to 10 gigabits per second
and many links use WDM -
wavelength division multiplexing -
to put several channels of signals
over one fiber.

6. Wavelength-
Division
Multiplexing
It is easy to understand WDM. Consider the fact that
you can see many different colors of light - red, green,
yellow, blue, etc. all at once. The colors are
transmitted through the air together and may mix, but
they can be easily separated using a simple device like
a prism, just like we separate the "white" light from the
sun into a spectrum of colors with the prism.

7. Wavelength-Division Multiplexing
The input end of a WDM system is really quite simple. It
is a simple coupler that combines all the inputs into one
output fiber. These have been available for many years,
offering 2, 4, 8, 16, 32 or even 64 inputs. It is the
demultiplexer that is the difficult component to make.
The demultiplexer takes the input fiber and collimates the
light into a narrow, parallel beam of light. It shines on a
grating (a mirror like device that works like a prism,
similar to the data side of a CD) which separates the light
into the different wavelengths by sending them off at
different angles. Optics capture each wavelength and
focuses it into a fiber, creating separate outputs for each
separate wavelength of light.

8. Wavelength-Division Multiplexing
Current systems offer from 4 to
32 channels of wavelengths.
The higher numbers of
wavelengths has lead to the
name Dense Wavelength
Division Multiplexing or DWDM.
The technical requirement is
only that the lasers be of very
specific wavelengths and the
wavelengths are very stable,
and the DWDM demultiplexers
capable of distinguishing each
wavelength without crosstalk.

9. CATV Technology
Today's CATV Systems include:
Hybrid-Fiber-Coax (HFC)
Overbuild on coax
Singlemode fiber
Lasers
Protocol: AM-Analog, digital
Mix video/data/voice

10. CATV Technology
The reason fiber is used in CATV
networks is that the fiber pays for
itself in enhanced reliability. The
enormous bandwidth requirements
of broadcast TV require frequent
repeaters. The large number of
repeaters used in a broadcast cable
network are a big source of failure.
And CATV systems' tree and branch
architecture means and upstream
failure causes failure for all
downstream users. Reliability is a
big issue, since viewers are a vocal
lot if programming is interrupted!

11. CATV
Technology
Applications in CATV were slow until
the development of the AM analog
systems. By simply converting the
signal from electrical to optical, the
advantages of fiber optics, especially
reliability, became cost effective. Now
CATV has adopted a network
architecture that overbuilds the normal
coax network with fiber optic links.
The HFC network lets the CATV
provider have a two-way connection to
the subscriber that allows them to offer
broadband Internet connections at a
low cost. The fiber network will also
allow easy conversion to digital TV
when it’s ready.

12. LANs
There are a large number of LAN standards today. The
most widely used, called Ethernet or IEEE802.3 after
it's standards committee, is a 10 MB/s LAN that
operates with a protocol that lets any station
broadcast if the network if free.
Token ring (most often referred to as IBM Token Ring
after its developer) is a 4 or 16 MB/s LAN that has a
ring architecture, where each station has a chance to
transmit in turn, when a digital "token" passes to
that station. Token ring has been abandoned by IBM
and is basically obsolete, although many networks
are still in operation.

13. LANs
Fiber Distributed Data Interface (FDDI) is a high speed
local area network standard that was developed
specifically for fiber optics. FDDI has a dual counter-
rotating ring topology with dual attach stations on
the backbone that are attached to both rings and
single attached stations that are attached to only
one of the rings, through a concentrator. It has a
token passing media access protocol and a 100-
Mbit/s data-rate. Like Token Ring, it is obsolete but
still in use for its fault tolerance.

14. LANs
ESCON )is a IBM-developed network that connects
peripherals to the mainframe, replacing "bus and
tag" systems. The network is a switched star
architecture, using ESCON directors to switch
various equipment to the mainframe computers.
Data transfer rate is 10 Mbytes/second. Newer
mainframes use Fiber Channel at higher speeds.
Fiber penetration in LANs is very high in long distance
or high bitrate backbones in large LANs, connecting
local hubs or routers, but still very low in
connections to the desktop. When simply replacing
copper cables, fiber is more expensive in a LANs,
but using a centralized fiber architecture makes fiber
more cost effective than copper in most cases.
Rapidly declining costs of the installed fiber optic
cable plant and adapter electronics combined with
needs for higher bandwidth at the desktop are also
making fiber to the desk more viable.

15. Centralized Fiber Architecture

16. Centralized Fiber Architecture
The traditional LAN cabling layout as described in the
original EIA/TIA 568 standard and shown on the left of
the drawing, follows telephone system designs from
decades ago. It divides the LAN into “horizontal”
cabling no longer than 90 meters, connecting the
desktop to a hub in a wiring closet. The horizontal
distance limitation is based on the maximum
performance of the UTP cables.
The “horizontal” cabling connects to a “backbone,”
which by virtue of bandwidth and distance
requirements, is generally fiber optics already. The
backbone connects all the hubs to a central
communications facility, usually called a main telecom
closet, where the complete LAN is managed and
connections to the outside world are terminated.

17. Centralized Fiber Architecture
Every closet must have a hub to interconnect the
desktop to the backbone, which requires space,
power, UPS, air conditioning and installation. Most
closets have punchdowns, patch panels and other
passive hardware too.
With fiber optic cabling, you aren’t limited to 90
meters. With fiber, you don’t need horizontal and
backbone links, you don’t even need a telecom
closet! You just need one link, a pair of fibers
straight from the desktop to the main telecom closet.

18. Centralized Fiber Architecture
You don’t need a hub, power and backup power for the
hub, racks and space for all that or installation and
maintenance labor. At most, with fiber you have an
intermediate passive patch panel to connect desktop
cables to the backbone cable and some extra (and
cheap!) fibers in the backbone cables.
With this architecture, fiber is usually much less
expensive than copper and will support new networks at
higher speeds for a long time in the future.

19. Links
Most datalinks are used
to connect two devices
point-to-point and lack
the protocols of a
network. Most of these
links offer fiber optics as
an option - and some are
only fiber.
RS232 and RS422 are
industrial links that have
been around for many
years. They have been
available on fiber since
fiber got started.
Types of Links:
RS232, 422
Fiber Channel
HIPPI
IEEE 1394 (Fire Wire),
Toslink
MOST, Flexray
(automotive, POF)
Video (analog or digital)

20. Links
Fiber Channel is a high speed link connecting
computers to peripherals like disk drives and printers.
HIPPI is a similar (and fairly obsolete) link.
Fire Wire and Toslink used in consumer applications
like digital audio.
Most and Flexray are automotive networks, where
fiber’s lighter weight and immunity to electrical noise
make it a better choice than copper.
Many video links are available on fiber optics, from
remote security cameras to broadcast TV cameras in
studios.