[AusNOG] Why not Symmetric ingress and egress?

[Paul Brooks]

On 17/06/2010 11:22 AM, Tim McCullagh wrote:
>
> ----- Original Message -----
>
>     *From:* John Lindsay <mailto:JLindsay at internode.com.au>
>     *To:* ausnog at ausnog.net <mailto:ausnog at ausnog.net>
>     *Sent:* Thursday, June 17, 2010 9:59 AM
>     *Subject:* Re: [AusNOG] Why not Symmetric ingress and egress?
>
>
>     There are also some limits in the FTTH network architecture that
>     mean there is less total bandwidth in the back channel.
>     *Not necessarily,  that may be true for GPON which is what NBN is
>     going to use, but GEPON equipment has no such limitation.   Even
>     for GPON it can hardly be used as an excuse to have a 25 down 5 MB
>     up etc.  Unfortunately with NBN we will be locked into GPON. *
>
Which variant of GEPON did you have in mind Tim? 802.3ah GEPON provides 
1.25 Gbps in both upstream and downstream directions. GPON has the same 
upstream capacity, with double the downstream capacity. Thats hardly "no 
such limitation".

As far as speeds and up/down ratios for individual services go, you have 
to look at the RSP's choice of packaging more than the choice of PON 
technology - and also recognise that the RSP (not NBN) has to backhaul 
all the traffic over the water to Tasmania which aint cheap, so may have 
very good reasons to currently offer a variety of speeds, at a variety 
of price points, to ensure there is something to suit everybody's budget.

>     *Some of the issues has come down to the choice of equipment
>     vendors.   As always in choosing a vendor big is not always better. *
>     **
>     *Much of the equipment deployed (presently) in Australia is not
>     the same vendor as NBNs choice. Other than Telstra, most
>     deploy Wave7 / Enablence kit in either GPON or GEPON or both
>     varieties.  Then there is some hills equipment.  Personally I
>     don't see why a GPON solution was chosen over a GEPON solution
>     other than that the GPON vendor was familiar to the powers to be
>     at NBN.   In fact I think it was a dumb choice, but that is just
>     my 2 bobs worth.  This is all really back to the future stuff.  I
>     wonder how long it will take to hear the cries from the public re
>     lack of competition and choice re NBN, in the same way as happened
>     in the 1970s. *
>

GPON provides twice the downstream capacity, the same upstream capacity, 
as GEPON. On the other hand, GEPON gear may be cheaper than GPON gear. 
GPON supports TDM services for legacy migration, GEPON does not. These 
are tradeoffs which will come out in the selection RFP process. NBNCo 
hasn't made a vendor choice yet for the main mainland rollout as far as 
I know, perhaps you have better inside insight.


>     **
>     *It strikes me that there are too many so called experts that have
>     never done any FTTH deployments that simply do not understand the
>     issues.  Fibre is sexy so we should do it stuff, when fibre should
>     be driven by a business case. *
>     **
>     *I really do pity the 55% of homes that are going to get aerial
>     FTTH, talk about recipe for disaster.  It isn't the same as
>     copper, you can't just scotch lock a bit into it when it gets
>     brought down by wind, fires trucks etc.   For those that want to
>     remind me about backhoe fade, yes that happens in one spot.   In
>     the case of fire and wind it will happen in many spots, over large
>     geographic areas.  Trying to reconstruct quickly will take time. 
>     You cant run fibre acress a driveway to effect quick repairs like
>     copper.  I could go on but I am already off topic.
>     *
>
I'm confused by this Tim - you first say that fibre should be driven by 
a business case, then in the next breath argue for underground 
deployment which is significantly more expensive than overhead. You 
worry about wind, and ignore that aerial fibre cable is lighter than 
aerial copper cable, and less affected by strong wind. You worry about 
overhead cabling and bushfires, ignoring that most suburban areas aren't 
close to any bush, and haven't seen bushfires for a hundred years - and 
in bushfire-prone rural areas, fibre is usually ploughed safely 
underground. In fact, all the downsides with overhead cabling you raise 
- which are all valid concerns by the way - apply equally to copper 
cables as well as fibre cables, so overhead fibre will not be any less 
reliable than the current overhead copper network.

The two countries with highest FTTP deployment are Sth Korea and Japan. 
Over 95% of Japan's FTTP deployment is on overhead cable. They've been 
doing it for a while now, I'm happy to call a few of them experts.

I realise your main point is that a fibre core takes longer to repair 
than a copper pair - which in an emergency can be quickly twisted or 
soldered to a new cable segment - but it also only takes 3 minutes to 
put on a couple of field-installable fibre terminations and plug them 
into a joiner. Quicker than waiting for the soldering iron to heat up.

Its not a black-and-white, right-or-wrong issue. There will be areas 
where overhead makes more sense than underground, and areas where the 
opposite is true. You use the most appropriate construction technique to 
suit the local conditions, which vary enormously across the country.

BTW Tim, which FTTH deployments have you done, and which GPON and GEPON 
gear did they each use??

Paul.

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