Phone Cable Question

[SUNRAY]

Fair enough - so they haven't implemented the back-up facility which, as above, I would have thought was desirable.

I feel that is just a little understated

In practice, of course, it's likely that in a fair proportion of cases, failure of the mains supply to the cabinet would be associated with failure also of the mains supply to the relevant customers - so the lack of battery back-up in the cabinet would make no difference.

Bearing in mind the potential for urgent comms requirements in the event of a power outage I'd have thought that shouldn't even be considered.

 

[Murdochcat]

So going back to very early in this thread, this photo shows how the BT full fibre appears inside my son’s place. It was installed in December last year

 

[JohnW2]

I feel very cleverly constructed "lump of glass" is just a little understated

Well, if that's what it is, that's what it is - even if it is extremely cleverly designed and constructed!

Countless things in this world are, in a literal sense, "a lump of something", but sometimes extremely cleverly designed and constructed.

 

[JohnW2]

I feel that is just a little understated ... Bearing in mind the potential for urgent comms requirements in the event of a power outage I'd have thought that shouldn't even be considered.

Things have changed in moire recent times with the ubiquitous possession of mobile phones, but if you go back a little earlier than that, countless people seemed happy to have only cordless landline phones (which would not function in the event of a power outage).

 

[SUNRAY]

I would still be intrigued to know how on earth it works. On the face of it, I would have thought that each such "lump of glass" would probably have to be 'bespoke' in every case (e.g. according to the number and identity of the individual customers and/or PoCs), but I can't believe that woud be practicable?

yes but those bespoke situations occur on pretty much every fibre circuit

Things have changed in moire recent times with the ubiquitous possession of mobile phones, but if you go back a little earlier than that, countless people seemed happy to have only cordless landline phones (which would not function in the event of a power outage).

Annnnnnnnd how many cell sites have battery backup?

 

[JohnW2]

Annnnnnnnd how many cell sites have battery backup?

We've been through that before, and I personally have no idea but I understand that you think the answer is "not many" (if any?).

If you're right, then, for a start, I would be a bit surprised. The government seem to have bought into the concept of using the mobile phone network to circulate 'emergency messages' in the event of, say, 'national disasters'. That being the case, one might have expected that they wouldin sist on those networks being resilient in the face of power outages.

 

[endecotp]

The splitters don't just split, they do WDM mux and demux.

My understanding is that what BT (and CityFibre, etc?) are currently deploying is GPON, “gigabit passive optical network”.

GPON - Wikipedia

en.wikipedia.org

The splitters are all passive, and it all uses two wavelengths, one for upstream and one for downstream. Multiple users are segregated using time-division multiplexing only.

I’m surprised by your comment about WDM in this context. I was under the impression that it was not used on these fibres. I do know that 10GPON uses different wavelengths, so in principle you could have gigabit and 10G on the same fibres for different customers.

 

[SUNRAY]

My understanding is that what BT (and CityFibre, etc?) are currently deploying is GPON, “gigabit passive optical network”.

GPON - Wikipedia

en.wikipedia.org

The splitters are all passive, and it all uses two wavelengths, one for upstream and one for downstream. Multiple users are segregated using time-division multiplexing only.

I’m surprised by your comment about WDM in this context. I was under the impression that it was not used on these fibres. I do know that 10GPON uses different wavelengths, so in principle you could have gigabit and 10G on the same fibres for different customers.

I must be honest and say I thought this was the more likely option purely on the grounds of cost but Dave's post seemed to carry authority.

 

[JohnW2]

The splitters are all passive, and it all uses two wavelengths, one for upstream and one for downstream.

That makes sense, but I'm not sure that I would call it 'multiplexing'

Multiple users are segregated using time-division multiplexing only.

Again that makes sense, and that multiplexing (and demultiplexing) is presumably is achieved by the electronics at each end, not (somehow?) happening passively within the light signal?

 

[JohnW2]

The splitters are all passive, and it all uses two wavelengths, one for upstream and one for downstream.

I should perhaps have added ... despite what has been suggested, I'm not sure that it requires a particularly cleverly-constructed l'ump of glass' to split a light beam (potentially very many ways) by frequency, does it? - I would have thought that a moderate grade in GSCE and a prism would probably be enough

Mind you, I'm still not sure I'd call that 'de-multiplexing' (or the converse 'multiplexing') - it would seem analogous to different users using different bits of the radio spectrum simultaneously, but I've never heard that called 'multiplexing'!