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FTTP network edge hardware

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Weaver:
If you have some sort of FTTP, what is the ONT / ONU hardware that you have?

Do Openreach users have PONs?

If someone does, they need the ONT to run the PON protocol, to split apart, decrypt the broadcast downstream and handle the time slots in the TDMA for the upstream, so there’s quite a lot in it.

Has anyone seen anything about the optical-to electrical very lowest interface layer and the PHY protocol layer if any immediately above it? I’m wondering about coding (or any possible modulation ?) on the wavelength(s) and I realise I don’t know the first thing about it.

Has anyone got straight optical link, ie without any PON-style sharing/broadcast/splitting/TDMA, so that you get the full capacity in both directions?

What about B4RN NICs? I know that you get the full 900Mbps upstream as well as downstream with B4xx, but I don’t know about any sharing with neighbours, at the optical level or in ethernet domains or wherever.

I’m amazed at how little I know about this so any links would be good.

What exactly do we call the types of optical access interfaces, direct or PON or whatever, and the nomenclature for types of PON if different variants are around. And what does one call the different types of ONT?


If I were ever lucky enough to get an optical interface, then I would want to put a serious lightning surge protector on the ONT’s mains and put it on its own huge UPS. I would also really want to try and beg a spare ONT (not for free) as well, in case it went belly up for any reason.

I realise that they have batteries in them. With a spare ONT, perhaps a UPS would be overkill, apart from its own anti-surge properties. I do of course realise that there is a dramatic reduction in lighting risk because there’s no longer any possibility of damage through the network, but my mains is still vulnerable of course. I wouldn’t need to worry about GPR/EPR anymore.

Ixel:
If you have some sort of FTTP, what is the ONT / ONU hardware that you have?

I have the 1+1 ONT supplied by Openreach, with the battery backup unit, connected via a UPS (my own of course). I presume if, for some reason, I ordered a second FTTP service then I'd be upgraded to a 4+2 ONT. This would be handy if I wanted a bonded or load balanced connection I guess, and if this option worked out more cost effective and/or reliable than just paying for one faster FTTP package (the pricing for 500/165 and 1000/220 is a bit steep for the moment).

Do Openreach users have PONs?

Other than the 1+1 ONT, my network is currently ethernet copper with a mixture of Cat6a and Cat5e cables.

Has anyone seen anything about the optical-to electrical very lowest interface layer and the PHY protocol layer if any immediately above it? I’m wondering about coding (or any possible modulation ?) on the wavelength(s) and I realise I don’t know the first thing about it.

I don't know a huge amount about Openreach's specifications and acceptable thresholds, other than -15 dB possibly being the minimum acceptable light level? I've obviously read up how some of the FTTP stuff works though, mainly for curiosity.

I doubt you'd ever be able to ask for a spare ONT, given they have to authorise the device for usage on their (Openreach) network, however you might be able to pay for some form of 'critical care' care level which has a fast turnaround time.

niemand:

--- Quote from: Weaver on May 25, 2019, 01:24:14 AM ---If you have some sort of FTTP, what is the ONT / ONU hardware that you have?

Do Openreach users have PONs?

If someone does, they need the ONT to run the PON protocol, to split apart, decrypt the broadcast downstream and handle the time slots in the TDMA for the upstream, so there’s quite a lot in it.

Has anyone seen anything about the optical-to electrical very lowest interface layer and the PHY protocol layer if any immediately above it? I’m wondering about coding (or any possible modulation ?) on the wavelength(s) and I realise I don’t know the first thing about it.

Has anyone got straight optical link, ie without any PON-style sharing/broadcast/splitting/TDMA, so that you get the full capacity in both directions?

What about B4RN NICs? I know that you get the full 900Mbps upstream as well as downstream with B4xx, but I don’t know about any sharing with neighbours, at the optical level or in ethernet domains or wherever.

--- End quote ---

Openreach supply FTTP over GPON.

Optical to electrical there's not much to say. It's not using any exotic higher order modulations. There is plenty of capacity available on the TX and RX wavelengths to ensure there's no need for phase shift keying or quadrature amplitude modulation. All binary, specifically scrambled Non-return-to-Zero code.

https://www.itu.int/rec/T-REC-G.984.1 - general characteristics
https://www.itu.int/rec/T-REC-G.984.2 - PHY/PMD

EDIT: Just FYI the scrambling doesn't refer to encryption but to scrambling the binary signal to ensure there's no profound bias towards zeroes or ones - without this any time the PON is sending nothing there'd be a series of null frames which isn't desirable, much better for transceivers to have a mix of 1s and 0s.

Optical link - B4RN use 1000BaseBX, single fibre, WDM to separate TX and RX, a media converter to present the connection to customer equipment as 1000BaseTX. This is point to point Ethernet, not a lot else to say. Ports will I presume be in the same broadcast domain though don't know for sure - depends on configuration.

Weaver:
I just realised that B4xx might well just be a giant fibre LAN, with straight ethernet and so fibre media converters.

I assumed that there wasn’t any higher modulation as I could not think of any need.

That scrambling is the usual thing then, to remove the danger of dc bias or at least very low frequencies caused by pathological data such as long runs of zeros or ones, as you say. DSL has the same thing does it not?

Many many thanks to all for the info and esp for the links.

If you have a bad joint optically, or dust in the physical interface, on the plug or inside the socket despite the door, then I suppose one could get errors. It is going to start relying on ethernet CRCs? (And then IP checksums)

niemand:
GPON transmission convergence layer, covering transmission error detection and correction - https://www.itu.int/rec/T-REC-G.984.3-201401-I/en

1000Base-BX does indeed use the mechanisms in 802.3z, the Gigabit Ethernet standard.

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