and businesses get their Internet service
via the cable TV system or the phone
company’s DSL lines. While both are
fast, they are running out of steam,
especially DSL. The ideal high speed
service is fiber but it is more expensive
at the moment. The ultimate goal is to
run fiber to the home (FTTH) and use it
to supply fast Internet access, phone
service via voice over IP, and IPTV.
PONs make this possible because
they are fast and reasonably inexpensive
due to their totally passive nature. For
long haul fiber networks, the signals must
be converted from optical to electrical
and back to optical (OEO) to rejuvenate
them in case of fiber loss and/or distortion. Such OEO repeaters are expensive.
By eliminating them and just running the
cables only, costs are cut dramatically
making PONs a viable alternative to
current methods like DSL and cable TV.
Asia (Japan and Korea, particularly) and some parts of Europe already
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use EPON, a system based on the
Ethernet standard. Data is transmitted
at 1 Gb/s downstream over the fiber to
the home on 1,490 nm where it
encounters splitters that divide the
optical signal and send it off to multiple
homes or businesses. A splitter is just a
passive light divider with no electronics. Splitters are available to divide the
signal by a ratio of 1: 4, 1: 8, 1: 16, 1: 32,
or 1: 64. A splitter is also a combiner
where it can take multiple light signals,
add them together, and send the
combination back to a central office.
The upstream data rate is also 1 Gb/s,
but it rides on a 1,310 nm wavelength.
In the US, Verizon has initiated its
FiOS system using a PON in some
parts of the country and selling the
service as the faster alternative to cable
TV and DSL. AT&T is also testing a
similar system for IPTV. Fiber is a bit
more expensive, but the basic date
rates are in the 30 to 50 Mb/s; many
times faster than conventional services.
It can easily handle multiple HDTV
channels, as well as VoIP phone service and Internet access. Several million
homes already use it and more are
being rolled out over the coming years.
The technology is referred to as
GPON or Gigabit PON. The basic
downstream data rate is 2.488 Gb/s
on 1,490 nm with a fast 1.244 Gb/s
upstream rate on 1,310 nm. A separate downstream wavelength of 1,550
nm is reserved for TV. While each
customer does not get the full 2.488
Gb/s speed, the system divides the fast
stream among the customers who are
served by passive fiber and splitters.
Fiber is widely used in 1 Gb/s and
10 Gb/s Ethernet LANs and in Fibre
Channel — a type of network widely
used in storage area networks, large
arrays of hard disk storage systems.
The fiber provides 1, 2, 4, 8, or 10
Gb/s of speed so that servers can
access data on the disk drives fast.
As prices continue to drop and
the pressure continues to build for
IPTV and faster services, fiber will be
more widely adopted further reducing
prices. Fiber truly is the fastest data
communications medium available
and it will grow at an even faster rate
as the demand for Internet speed and
bandwidth continues. NV