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Topic # 79880 23-Mar-2011 21:48
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http://www.nzherald.co.nz/business/news/article.cfm?c_id=3&objectid=10714414

What does "segment will be shared between as many as 24 residential customers" mean? I thought fibre is like copper and that everyone gets a single line. Don't tell me fibre is like cable where everyone shares a line.

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  Reply # 451261 23-Mar-2011 22:21
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the P in GPON is for passive, it splits the one signal passively with low cost stuff in the street and the same signal goes to several customers with it being shared between them, not like ethernet which is a 1:1 connection on a single fiber




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  Reply # 451274 23-Mar-2011 22:58
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To elaborate,

Im not an expert but
At the Head unit it has something like 2gbit of transmission capacity
And that is shared among the attached users - like 30mbit each or 100mbit each depending upon the configuration. I think you can assign different capacities to different nodes to create tiered service or plans.

As the trunk fibre cable goes up the street, optical light splitters then divide the light and send it down a branch to a reciever box at the patch panel in your garage.

Also unlike cable - you have a maximum of something like 128 client nodes. Copper cable can have something like 200 nodes attached - They just put in RF amplifiers and extend the signal until the line noise doesnt allow them to extend it any further. I cant find an exact number but with high quality cable I would expect maybe 200 nodes or more - with the much more limited bandwidth of ~300mbit - and thats if they use all 8 downstream channels.


Edit: Just checked the wikipedia - http://en.wikipedia.org/wiki/Gpon
Its TDMA so you can get some very high speeds.

http://www.pmc-sierra.com/ftth-pon/ftth_overview.html
GPON = 2.25 gbit total downstream transmission / 1.25gbit upstream

http://en.wikipedia.org/wiki/DOCSIS
DOCISS 3 - The current modern cable system uses up to 8 channels each carrying 38mbits so a maximum downstream transmission capacity of 300mbits - 100mbit upstream


So some ratios:
A 100 node DOCISS 3 cable network using 4 channels = 1.5mbit per customer
A 128 node GPON fibre network = 17.57mbit per customer.

I suspect that even 1.5mbit is overkill and they probably wouldnt even need that on the cable.




Ray Taylor
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  Reply # 451291 24-Mar-2011 02:08
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GPON (one fibre passively split between x customers) vs Active Ethernet (one fibre to every customer back to a local active switch/router).

We've had a few long threads on it before.

The cliff notes are: GPON is slightly cheaper to deploy upfront and supposedly much cheaper to run (lower power) over time.

Personally I think it's a mistake and short sighted!

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  Reply # 451310 24-Mar-2011 08:28
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its ok, once gpon is incapable in a few years time, we can dig everything up and put in more cables.

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  Reply # 451314 24-Mar-2011 08:31
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So if I plugged my own kit into the fibre I could then snoop on all my neighbors traffic? And potentially use their internet?




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  Reply # 451430 24-Mar-2011 13:31
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exportgoldman:
So if I plugged my own kit into the fibre I could then snoop on all my neighbors traffic? And potentially use their internet?


Yes but they must use some sort of massive encryption system.
Also i imagine its possible that only certain bands of lightwave get split off. Dont know for sure tho.




Ray Taylor
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  Reply # 451475 24-Mar-2011 14:50
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exportgoldman:
So if I plugged my own kit into the fibre I could then snoop on all my neighbors traffic? And potentially use their internet?


No, it'll be encrypted. Depending on the implementation, each premises will have a separate light frequency for the upstream.
 

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  Reply # 451565 24-Mar-2011 19:27
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GPON has an encapsulation method that isolates each drop, so no you cannot snoop. And no its not light channel isolation, all down and upstream traffice share the same light channel, the isolation/encapsulation below that.

Cyril

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  Reply # 451989 26-Mar-2011 11:00
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kyhwana2:
exportgoldman:
So if I plugged my own kit into the fibre I could then snoop on all my neighbors traffic? And potentially use their internet?


No, it'll be encrypted. Depending on the implementation, each premises will have a separate light frequency for the upstream.
 


All downstream traffic transmitted by the OLT shares 1490nm wavelength, and upstream uses 1310nm. 1550nm is available for video if connected to a headend. You could potentially snoop on downstream traffic only, since the splitters don't redirect any upstream traffic.

Singlemode optics are not like copper, so you can upgrade the terminals while using the same fibre. 10 Gigabit PON (1577 nm down / 1270 nm up) can be shared with GPON wavelengths to allow for incremental upgrades without disruption to other users.

If the fibre has been designed with enough cores in the feeder cable then you can use that same fibre to get an Active Ethernet link dedicated just to your connection. You might still have to share the bandwidth but maybe your ISP will give you a better contention ratio since Ethernet is more expensive.

Fibre does not carry electricity of course, so your power supply and battery backup etc are likely to be more important than any bandwidth issues.




Qualified in business, certified in fibre, stuck in copper, have to keep going  ^_^

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  Reply # 452455 27-Mar-2011 16:49
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raytaylor:
exportgoldman:
So if I plugged my own kit into the fibre I could then snoop on all my neighbors traffic? And potentially use their internet?


Yes but they must use some sort of massive encryption system.
Also i imagine its possible that only certain bands of lightwave get split off. Dont know for sure tho.


GPON uses AES-128.

However, layer 1 encryption should never be relied upon for security. 

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  Reply # 453650 30-Mar-2011 22:48
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Ragnor:
The cliff notes are: GPON is slightly cheaper to deploy upfront and supposedly much cheaper to run (lower power) over time.

Personally I think it's a mistake and short sighted!


This is probably getting into off topic and (unintentional) flame-baiting territory, but I couldn't agree more.

*ducks out of thread*

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  Reply # 453652 30-Mar-2011 22:56
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Perhaps it's time for a super ultra mega UFB/RBI Thread?

GPON offer's better uptimes if only for the fact that from the OLT to the ONT is passive, An active network would require UPS's up poles etc etc. I remember well the amount of citylink outages caused by power faults affecting only a couple of streets yet taking out fibre for blocks.

But anyway, Time for a combined thread? There is alot of misinformation and speculation flying around




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  Reply # 453655 30-Mar-2011 23:02
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Wasnt the original spec ment to be dark fibre only, then changed so a wholesale layer 2 service could be provided, but dark fibre still avaliable for those who want to build their own layer 2 service by renting the dark fibre and colocating switcing gear inside the fibre co's cabinets?




Ray Taylor
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There is no place like localhost
For my general guide to extending your wireless network Click Here




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  Reply # 453659 30-Mar-2011 23:13
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My memory is a little rusty but I believe so but then someone worked out the numbers aswell since the initial spec called for unconstrained 100mbit between 2 homes in the same UFB zone. IIRC someone worked out that Hamilton would require 200 gbit/sec of switching fabric which and this was based on 50% uptake in Hamilton (50,000 homes) alone. This number also factored in for 10:1 contention so real raw layer 2 would be 2 tbit/sec uncontrained - As you can gather this just wasn't realistic

Dark Fibre is still and option from what I've seen, Anyone on PON can have their strand removed from the optical splitter and feed into either your gear at OS site or plugged into the backhaul cable and spat out at the OLT site, Do this again on the other leg and you can have Dark Fibre from anywhere to anywhere within the network for cheap




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All comment's I make are my own personal opinion and do not in any way, shape or form reflect the views of current or former employers unless specifically stated 

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