Wholesale FTTH implementation
jfmezei_nanog at vaxination.ca
Fri Oct 26 08:12:49 UTC 2012
In Canada, there is an emerging wholesale ISP model where the regulator
(CRTC) forces incumbents to make their last mile available for
competitive retail services. This regulatory regime does not YET
include FTTH last mile.
To this end, I have some questions about FTTH deployments. Any answer to
any of the topics is appreciated as it will give me better understanding
of some of the technical aspects.
*** 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 ?
*** 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 ?
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 ?
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 ?
>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
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.
*** 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 ?
**** 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 ?
>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
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 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.
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