Wholesale FTTH implementation
khelms at ispalliance.net
Fri Oct 26 17:10:49 UTC 2012
On 10/26/2012 4:12 AM, Jean-Francois Mezei wrote:
> *** Wavelengths (ok, this is a newbie question :-)
> It was my understanding that lasers were on/off devices which
> transmitted bits very fast. But I suspect I am very wrong on this
> because this doesnt seem to support RFoG deployment by cable, nor the
> Verizon FIOS which allocates some spectrum to TV and some to data.
> Anyone have a good pointer on how the lasers in an FTTH/GPON function ?
> Are they able to produce a wide range of "colours" and modulate signals
> ? Or are they really a bitstream with a single narrow colour and it is
> the hardware at both ends which converts between multi frequency
> broadcast signals and light pulses ?
Ok, the first thing to understand is that there are a lot of FTTH
technologies and they really work very differently from each other. I'll
describe three of the more common ones, but these are far from the only
RFoG (RF over Glass) is simply taking the DOCSIS HFC network to the
extreme where each home has its own fiber node in the nid. In this case
there are generally only two wavelengths active on the glass, one for
the upstream side and one for the down stream. Inside of those
wavelengths things are further sub-divided into 6 Mhz (8 for EuroDOCSIS)
wide channels on the downstream and 6.4 Mhz on the upstream. (3.2 if
you're running modems older than DOCSIS 2.0). You can run RFoG as an
overlay on an existing GPON installation and in that case the DOCSIS
signalling is encapsulated inside of the PON layer 1 and layer 2
transmissions, but in my experience this is relatively uncommon.
GPON (Gigabit Passive Optical Networking) is a technology that allows
for multiple wavelengths to be sent down a strand (16/32/64) which is
then split by a passive prism (no power or brains) to serve the
households attached to that splitter. This is a pure data delivery
mechanism so in many cases TV line ups are done as IP streams, however
you can work with specific vendors to have the TV channels delivered
separately in a normal MPEG2/4 stream that "normal" digital set top
boxes can handle once its been converted to RF in the home. (This is
the approach that Verizon took). Its also common to keep some amount of
copper in the loop and instead of running fiber all the way to the home
its run to a cabinet in a neighborhood and from there VDSL2 (with
vectoring if possible) is the local distribution loop. This gets rid of
the need for batteries in customer's homes and doesn't create a big drop
in speed. This can only be done within about 4000 feet of the cabinet.
Active Ethernet is yet another way of delivering services over a fiber
plant and it requires the least amount explanation since it really works
very similar to how ethernet works in normal enterprise networks and its
a baseband technology. Having said that it can (and often is) combined
with either course or dense WDM (Wave Division Multiplexing) to help
keep the fiber count down and that does use multiple wavelengths.
> *** ONT Selection
> Are there standards similar to DOCSIS where in theory, any ONT *should*
> work on any GPON system ? (with carriers only qualifying a limited
> number of models on their system). Or does the selection of the OLT and
> line cards determine a narrow set of ONTs that are compatible ?
> Or does it get down to each carrier getting custom made ONTs for the
> system they are deploying ?
In general you find out from your OLT vendor what ONTs they work with
other than their own. If you're in an open network scenario you'll have
to get this from the infrastructure owner.
> Do most ONTs on the market generally allow end user access to some of
> the config/status data to help in debugging problems ? or are they
> generally inaccessible by users ?
They seldom if ever allow end user access. You should find out exactly
what technology is being used, since some have decent stat reporting
(DPoE) via SNMP while others use TR-069.
> In the case of Bell Canada, I have obtained the following 2 images:
> http://www.vaxination.ca/temp/ont1.jpg outside equipment
> http://www.vaxination.ca/temp/ont2.jpg indoors equipment
> The ONT appears to be the alcatel-lucent equipment indoors. Would this
> mean that the outdoor equipment really acts only as a demarc which would
> be just a passive optical connector to join the patch cord to indoors
> CPE with the optical cable coming from the telephone pole ?
You'll have to get the details on this from the infrastructure owner,
there are tons of options for operators to choose from on indoor versus
outdoor using the same technology.
> >From what I have seen, Verizon FIOS uses an "all-in-1" ONT that is
> outdoors and provides ethernet, POTS phone and coax for TV services. So
> each carrier appears to have different approaches. (and Verizon also has
> spectrum dedicated to TV, spectrum to data and some to voice, which
> looks like a hybrid RFoG system).
> *** IPTV and packet priority/QoS/rate-limit
> In the case of Bell Canada, they have an IPTV service and they use twin
> PPPoE sessions on twin VLANs. One is the data connection to/from the
> BRAS, and the other is the IPTV stream from the Mediaroom data centre.
> (in the second picture, this would be handled by the black equipment on
> the left which would be the router that does the PPPoE sessions and
> outputs ethernet data and MoCA)
> In their VDSL2 environment, the DSLAM enforces QoS to give IPTV packets
> priority, reducing data througput to ensure it fits within the limited
> copper speeds.
> In an FTTH system, how would this be accomplished ? Would QoS and rate
> limiting be done by the ONT (since it is the new choke point where
> subscription speed is imposed), or would the OLT rate limit each end
> user's total bandwidth and prioritise IPTV packets to ensure it all fits
> whn it gets to the ONT's rate-limit ?
> Based on what I heard, those on Bell's FTTH have their IPTV streams fit
> within their subscription speed, so if they only subscribe to 16mbps
> service, and use 7mbps for IPTV, they only have 9mbps left for data.
It _CAN_ be done by the ONT/OLT together, but that's a
> *** POTS Service
> >From a POTS service point of view, is it easy to specify that customer
> X's SIP traffic goes to server A, while customer Y's traffic goes to
> server B ? (aka: allow CLECs to provide VoIP service to end users)
> Does the ONT get the SIP server destination when it is provisioned or
> does it talk to the OLT and it is the OLT which routes voice traffic to
> the SIP server assigned to that customer ?
Again, this one just depends on how the underlying carrier built it.
Having said that if its not prioritized SIP traffic (unless the operator
prioritizes all RTS data) it will simply be IP traffic that will go to
where ever the SIP endpoint (phone, ATA, etc) is programmed to send it.
If that route crosses the Internet WAN connection it can have QoS issues.
> **** Installation costs
> If a carrier has been installing FTTH systems for about 2 years now,
> would its installation costs have become fairly stable by now, or would
> they still be going down as the carrier optimises its processes and has
> more trained crews ? How long does it generally take before they have
> stable installation costs ?
It goes down some past the first two years but generally the biggest
drop is during the first 12-16 months and those are process and crew
experience related while the costs that drop after that tend to be
driven by CPE costs dropping.
> >From the information I have gathered, Bell uses Corning Flexnap on the
> telephone poles to connect lines to individual homes. Those are custom
> made at the factory for each street block (based on distances where each
> line to home will be). Is this fairly common method ? Or is it
> considered a more expensive method used by carriers with fewer trained
> employees ?
> If a carrier is using Flexnap to save on cable termination/connection
> manhours, would they also order pre-cut fibre cable runs between the
> flexnap on the telephone pole and each home ? Or would those be cut and
> terminated on the field ?
> And out of curiosity, in a Flexnap setup, what happens if a couple of
> fibre strands between two poles are damaged by a squirrel ? Does this
> mean that they have to manually splice the lines from the affected homes
> into spare strands on the cable ?
I don't know enough about Flexnap to comment.
> I appreciate any guidance/information you may provide. The more
> information I can provide to the regulator, the more informed a debate
> there can be and thus a better regulatory decision.
> Jean-François Mezei
> Vaxination Informatique
> Montréal, Canada
Vice President of Technology
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