GPON - How many houses on a port?

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Yabanize

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#190817 13-Jan-2016 18:37

Hi, I've been reading about how GPON shares a single OLT port with multiple houses, Im wondering how many a single port is shared between in NZ?
In Christchurch (Enable) if that is any different

Also, How does collision avoidance work? Because there are multiple houses, and each house has to transmit and receive at the same time

Talkiet

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#1470255 13-Jan-2016 18:58

http://lmgtfy.com/?q=how+does+gpon+work

The split is I believe either 24 or 32 depending on the LFC. Not 100% sure on that .

Some of the details at the link above (And I did check, most of the top hits are relevant and suitable) will tell you about the way it works. It's different up and downstream but I don't want to give away the whole plot...

Cheers - N

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Behodar

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#1470256 13-Jan-2016 19:02

I believe that each house uses different colour light. The difference is (probably) imperceptible to the human eye (not that you should be shining it into your eye in the first place!) but the equipment is sensitive enough to figure it all out.

DarkShadow

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#1470274 13-Jan-2016 19:05

Not that you can see it - it's infrared.

Publius

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#1470275 13-Jan-2016 19:06

GPON in nz generally has no contention issues, at least up to 100Mbps anyway (the dunedin gigatown is in theory completely over-contented in terms of GPON bandwidth, but hey it's cheap!)

The split is up to each LFC, i've heard Chorus are doing 16-way (IIRC), I think 24-way would be the max i've heard, although GPON allows higher.

GPON is curious beast, collusion avoidance is needed only on the upload leg which is a shared laser frequency. It's like mobile in that you get allocated time slices to talk on. Sounds simple right, but each upload laser can be different distances from the receiver, so has to take that into account too.
All in all, it works very well as the LFC's control the ONTs so everything remains compatible and well tested. I can't see them ever welcoming a world like dsl where you could provide your own ONT.

Talkiet

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#1470286 13-Jan-2016 19:06

Please note all comments are from my own brain and don't necessarily represent the position or opinions of my employer, previous employers, colleagues, friends or pets.

Chorusnz

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Chorus

#1470536 14-Jan-2016 09:12

We got Elliott Bonnett (Cheif Network Architect at Chorus) to provide a response.

>>

Upstream and downstream multiplexing uses two different techniques to share the common fibre communication channel. In the downstream direction each ONT is addressed individually. Frames are transmitted on the PON from the OLT and are received at all ONTs. Only the ONT the information is addressed to passes this to the end user, all other ONTs drop the information (this functions much as early multiaccess Ethernet configurations do). In the upstream direction a TDM protocol is used, where timeslots are allocated to each ONT as required, and only one ONT then transmits at any one time.

Initially Chorus' most common optical split ratio was 1:32 for the initial couple of years of deployment. The ITU GPON standard supports up to 1:128, but the physical limitation is an optical budget of 28dB.

We moved to 1:16 in conjunction with an Architectural change which also saw us move from housing splitters in above ground cabinets to smaller below ground fibre closures.

We also use a range of split ratios, down as low as 1:2 in rural, to increase reach. Each 1:2 split reduces power levels by 3dB. At an average loss of 0.4dB per km, each halving in the reduction in the split ratio gives us around 7 to 8km of extra reach in rural.

>>

^GL

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johnr

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#1470543 14-Jan-2016 09:24

Talkiet:

LOL love it

Publius

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#1474185 18-Jan-2016 21:42

@Chorusnz Thanks to you both for that awesome reply! Interesting about rural and split ratios. I understand rural copper is thicker than urban which has the side affect of dsl going further (db loss per m is lower with thicker copper), is there not some "low loss" fibre equivalent for rural?

Edit: spelling

toejam316

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#1474251 18-Jan-2016 22:56

Pretty sure for the Huawei stuff used by UFF (and I'm gonna venture a guess that it's similar for Enable) they use a 1:16 split, too. I don't know what the initial split was, it might've always been 1:16, but I'm pretty sure that's the current.

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Intravix

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#1484032 3-Feb-2016 08:25

toejam316: Pretty sure for the Huawei stuff used by UFF (and I'm gonna venture a guess that it's similar for Enable) they use a 1:16 split, too. I don't know what the initial split was, it might've always been 1:16, but I'm pretty sure that's the current.

Splitter ratio is quite often up to 1:32 for UFF.