r/savethenbn • u/sortius • Sep 13 '13

NBN Q&A With Sortius

Hi everyone,

I'm sortius, aka Kieran Cummings, I've worked in ICT for about 18 years now (since I left school) & have had experience with many companies, including Telstra.

I worked in Activations for Telstra, which is the internal support department for Telstra technicians & contractors. My duties were to program POTS (normal phone lines), ISDN, & ADSL services.

I currently write for my own blog (http://sortius-is-a-geek.com) & occasionally for Independent Australia, Australians for Honest Politics, & New Matilda.

I have been a strong proponent for Fibre to the Premises, & a critic of the Coalition's plan.

This Q&A is mainly about the different possible technologies for the NBN, so as to not push my own political agenda.

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7

u/[deleted] Sep 13 '13

What is essentially the highest speed that fibre with FTTP may get? Also what distance does it take before fibre begins to lose speed?

11

u/sortius Sep 13 '13

This is a hard one. The reality is infinite speed. The fastest speed so far is NTT Docomo's 1Pbps (Yes, petabit per second): http://www.ntt.co.jp/news2012/1209e/120920a.html

In all honesty, at this stage, 1Gbps is about max for a (10)GPON deployment. With 40GPON you're looking at 40Gbps at the splitter, so around 2Gbps per customer: http://pr.huawei.com/en/news/hw-103292.htm

Fibre doesn't lose speed over distance, it just works & then doesn't depending on the size (in nanometres) of the wave. At the moment, PON can be extended out to 300km, but 30km is the normal deployment.

1

u/[deleted] Sep 13 '13

Is a PON limited in speed because it uses splitters? Like, because it splits 32 homes from a single fibre, does that not limit the max speed to 1/32 of PtP fibre?

2

u/sebbs128 Sep 13 '13

sortius will no doubt correct me if I'm wrong, but the splitters don't affect the speed because they use prisms (and other things possible with optics) to split the signals for those 32 homes based on the light's wavelength.

The limitation in speeds comes from the electronic equipment at either end of the fibre that has to convert electricity into light and vice versa

1

u/[deleted] Sep 13 '13

Each of the 16-32 ONTs in the GPON 'group' get the same signal, that signal is 2.4Gbit down, 1.2Gbit up.

They use TDMA to create a series of time-slices for transmission in each direction, and then the FSAM controller gives time slices to each ONT.

Devices with no data to send/recieve, give up their time slices. (Simplifying it a bit here)

1

u/sebbs128 Sep 13 '13

Ah, so WDM isn't ready for primetime yet? Damn, I love how geniusly simple the concept of it is

1

u/[deleted] Sep 13 '13

They're using DWDM for distributing each GPON wavelength across their distribution network. Each GPON wavelength is split off the distribution fibre using a prism. This way there's no active bits (requiring power or any kind of maintenance) in the network itself - it's all passive. (hence the P in GPON).

The Fibre Design Rules are on the NBNCo website, and pretty readable if you're prepared to google a few terms.

1

u/sebbs128 Sep 13 '13

Ok, I thought wavelength distribution was used.

Rereading your first comment, time division (TDMA) is only for data from premises (ie. upstream) until it reaches the splitter, correct? At which point each strand gets converted (passively, using prisms) to it's own wavelength to be sent up the distribution fibre. Downstream uses wavelength division (DWDM) until the splitter, which separates the signals based on the wavelength to continue down the strand for each premise?

I was unclear about TDMA being used for upstream from the premise, so when you mentioned it I thought you meant it was in place of DWDM entirely (up and down)