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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]

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.

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.

[burakkucat]

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.

Yes, precisely.

[Weaver]

Has anyone ever seen anything written up about problems with optical links due to bad joints / fluff / crud ?

I presume if one takes the plug out and leaves it around the place so that the cat can play with it or chew it is asking for trouble because of crap on the end surface or the surface getting damaged.

I suddenly realised something. If one gets a spare ONT out of Openreach then it needs to be programmed for the slot(=line) it is living in, or does it? Is there some protocol for zero-config?

That’s because it needs to know which part of the downstream traffic is yours and how to decode whichever slice it should be looking at, no?

I don’t know if any random ONT would even work. Zeroconfig would be handy for the engineers of course.

If I were truly obsessed with having a spare, I could ask AA to get me one and I would think they would beat Openreach up for me. They are very keen on encouraging and helping you achieve top reliability. Might one way be me paying for a callout for an engineer to just come out with a new unit and that’s all? So a very quick job. Burakkucat got a unit on eBay - which either would just work with zeroconfig or would need someone to program it.

Thinking about it, it’s a security threat isn’t it? Openreach don’t want the units floating around and people fiddling with them so that they can eavesdrop on the neighbours. If you were daft enough to sell your own working unit on eBay then presumably the next door neighbours could buy it and eavesdrop you? Or would it detect that it’s on the wrong line and squeal? So in that case there would be a minimal protocol but not full zeroconfig. It would help if I had already read the standards documents but a lot of pain at times today. Poor excuse. I’ve been writing code instead of reading today though.

Sanity check: If you have an expensive business ‘ethernet’ link (eg https://www.aa.net.uk/ethernet/how-it-works/) is there no GPON? So no mux-ing of upstream so that you get full speed not a miserable 30Mbps u/s ?

[Ixel]

I suddenly realised something. If one gets a spare ONT out of Openreach then it needs to be programmed for the slot(=line) it is living in, or does it? Is there some protocol for zero-config?

As I stated earlier on, the engineer has to authorise the ONT (at least by means of a specific serial number, whether other details are taken into consideration I don't know). If I understand correctly, as I wasn't observing the entire installation process when mine was being done, they scan the bar code stuck on the ONT in order to authorise it. Even if A&A want an engineer to come out and provide a spare ONT, and they actually managed to achieve this, the ONT would still need to be authorised by an engineer which no doubt would mean they'd have to arrange an appointment and turn up at the premises. There's also another caveat, handling the fiber optic cable. The end of the cable can be sensitive to things like dust so you may need to get a special cleaning wipe to clean it before plugging it in to the replacement ONT. All it took was a slight bit of a rain drop on the end of my fiber optic cable at the connectorised block terminal to disrupt my connection completely (engineer obviously went back to pole and fixed it, as there was a bit of light rain that afternoon unfortunately).

Sanity check: If you have an expensive business ‘ethernet’ link (eg https://www.aa.net.uk/ethernet/how-it-works/) is there no GPON? So no mux-ing of upstream so that you get full speed not a miserable 30Mbps u/s ?

I believe I'm correct when I say that it doesn't go via a splitter or aggregation node, unlike FTTP. It's a direct fiber optic link from the premises to the exchange and is uncontended.

[niemand]

https://support.huawei.com/enterprise/en/doc/EDOC1000078313?section=j00k&topicName=gpon-terminal-authentication-and-management

[ahmedfarazch]

Hello!


For the HG8247H we have, authentication is via the serial number of the ONT and a configuration profile is applied by the OLT/ISP after a reset to factory defaults as soon as the PON light turns stable (green). MAC Address Binding is also used for the services provided. Usually, ISPs don't allow third party ONTs, but, ones from same vendor supporting same OLT should work. Furthermore, ones from Ubiquiti can support the Huawei's serial number authentication and can also work: https://community.ubnt.com/t5/UFiber-GPON/UFiber-Nano-G-GPON-Huawei-HG8245-Configuration/td-p/2139059 (they do however encourage seeking approval from the ISP and to verify support with the OLT)!

Regards,
Ahmed

[IanG]

Has anyone ever seen anything written up about problems with optical links due to bad joints / fluff / crud ?

If you are assembling a list of possible faults, don't forget the minimum bend radius.

[Weaver]

Ian that’s a very good point. Is there anything mechanical /structural that can help a little bit to prevent violation of the minimum bend radius constraint - unless you have an accident or go out of your way to knacker it?

[IanG]

I did look at some specifications for fibre drop cables, but found no mention of minimum bend. On reflection (no pun intended) it should not be an issue for the drop catenary, but for the extension that presumably would snake down the side of the house. Some cables allowed an unsupported drop length in excess of 100 metres.

One specification also said that the cable was resistant to gunshot, a hazard that I not considered.