Regis, MikeM, Thread,
One cannot compare ONUs to PONs, for they are two
distinctly different types of network elements.
An optical network unit or ONU is a field node that
terminates fibers from the passive star couplers upstream, in
the case of PON networks, and may contain channel units which
are I/O ports for specific types of services. POTS, ADSL, T1,
VDSL, ISDN, etc. We have to be careful here, because ONUs are
also used in topologies other than PON.
A passive optical network, or PON, in contrast, is the fiber
distribution component of the deep fiber neighborhood
network which is comprised of fiber optic strands and
passive star couplers. The couplers do not use
amplification, thus they are considered passive. And this is
where PON derives its passive name.
The coupler may have a single strand going into it (from the
central office or HDT) and up to 32 strands coming out. Each
of the 32 strands coming out in turn, terminates into a field
Optical Network Unit, or ONU. From the ONU individual
conductors of various types are sent to businesses and
residences. The type of media is specific to the type of
service; the distances involved; and the manufacturers' and
providers' preferences, where options are available.
Whereas ATM Passive Optical Networks or APONs use this
topology, other direct means are available, using similar
approaches. I am not certain what the DISC*S range of options
is, but you can get a sense from the following:
From the Marconi site:
Integrated Voice, Video and Data Over a Single Fiber
The Marconi Fiber-to-the Curb (FTTC) approach - DISC*S
FiberStar -- is unique and innovative. A single-mode,
bi-directional optical fiber carries voice, video and data signals
between the DISC*S Host Digital Terminal (HDT) and an
Optical Network Unit (ONU) located near the customer
premises. Each ONU can serve seven to eight single-family
homes or 10 to 12 apartments.
[[fac edit: Note, at this juncture is where the passive 12-
strand/or 12-port coupler may be used.]]
The ONU is positioned within 500 feet of the end-user, so no
passband modulation is required (eliminating the attenuation
and crosstalk problems of competitor systems located at
greater distances). The 500-foot proximity of the DISC*S
ONU enables virtually unlimited, symmetrical high-bandwidth
transport over existing twisted-pair copper wire or coaxial
cable."
--------
The "low powered" ONU has no special (or comparative)
significance vis a vis PONS, here. It's called low powered
simply because it consumes far less power than previous (or
other manufacturers') ONUs, according to the claims of the
vendor.
---------
Do I think that the variety of speeds and contrasting standards
is all marketing hype? Absolutely not, although I have some
doubts as to the affordability of the higher rates to residential
users.
But for the business variety of users, and for schools and
municipal offices, etc., I can certainly see GE being deployed
at some point in time, and certainly 100 Mb/s now. Maybe the
100 Mb/s to SOHOs, and definitely 10 BaseT to residentials
now. What I suspect, however, is that the ILECs will continue
to cling to the DS-0 value basis, and charge inordinately high
prices for the higher speeds, in comparison to the decreasing
costs which they will enjoy through optical economies. I have
no foundation for this yet, but it's just a gut, and I hope I'm
wrong.
You must remember that when you consider the range of
services available from FTTC architectures, you have to
divorce your present thinking from your your previous notions of
what the cable modem model based on HFC ystems are capable of in
the data services space.
Where HFC normally only delivers up to 38 Mb/s maximum,
over a single 6 MHz channel, which is then reduced radically
to something less than 30 Mb/s, and must then be shared by
500 to 2000 users, FTTC now brings the potential for
multi-hundred gigabits per second to the ONU, to be
distributed to a comparatively smaller number of users over
shorter distances. Night and Day, and whole new vistas open
up.
You can think of FTTC in some ways as a fiber optic
backbone extension to a LAN closet in a corporate setting,
say, on the 15th floor of an office building, or a multiple media
access unit on a trading floor which is no different than those
bay/nortel and 3com 100 mb hubs being used there today.
There would be no material difference, save for possibly
some penalties incurred in the way of diminishing bit rates
(still in the multi-gigabit aggregate range potential, however) if
distances were severe, causing the fiber optic loss budget to
begin to suffer.
Some helpful links from the Marconi site follow.
marconicomms.com
The option exists to use either fiber or copper to the user
termination point, as stated:
"Most communications services can be deployed directly
from the DISCHS Host Digital Terminal (HDT). Or, to
extend the reach and optimize the speed and reliability of
service delivery, use DISC*S FiberStarTM or DISC*S
CopperStarTM technology."
marconicomms.com
I would look for a little peer review here, folks. Tim,
Bernard, Denver... speak up. I know that I must have some
of the Marconi issues either overly abbreviated, or
misconstrued. Then again, maybe not. I did not find the level
of detail in their description on their web site, to be
absolutely comfortable and sure.
Comments welcome.
Regards, Frank Coluccio
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