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[niemand]

A bit more was discussed than is in the deck and it had to be kept simple to keep within the 25 minute time limit but just in case you're interested.

Next Generation Fixed-Line Broadband

[Alex Atkin UK]

As they move stuff away from exchanges, I wonder where LLU fits in all this?

There is potentially a very real benefit to an ISP having Netflix, YouTube, etc, caches actually in the exchanges so their customers never need to hit their backhaul at all for certain traffic.  Is doing this only in very large exchanges enough?  Although obviously a small exchange wouldn't have space for the equipment anyway, but naturally being less customers also would negate any benefit anyway.

[aesmith]

Looking at the ninth slide, and basing on the comments in one of my threads, is there really a link from Openreach's FTTP into the PSTN? 

[niemand]

Looking at the ninth slide, and basing on the comments in one of my threads, is there really a link from Openreach's FTTP into the PSTN?

Kinda - I think whomever made that image didn't want to overcomplicate things.

[niemand]

As they move stuff away from exchanges, I wonder where LLU fits in all this?

It doesn't beyond having own links to the aggregation points much as they have their own links to the existing OLT/L2S rather than having BT Wholesale deliver the traffic to them.

There is potentially a very real benefit to an ISP having Netflix, YouTube, etc, caches actually in the exchanges so their customers never need to hit their backhaul at all for certain traffic.  Is doing this only in very large exchanges enough?  Although obviously a small exchange wouldn't have space for the equipment anyway, but naturally being less customers also would negate any benefit anyway.

This is already done in a very, very few cases. Were Openreach to collapse the ~1000 headends to 200 it would make a lot of sense to do so more widely.

[Alex Atkin UK]

It doesn't beyond having own links to the aggregation points much as they have their own links to the existing OLT/L2S rather than having BT Wholesale deliver the traffic to them.

This is already done in a very, very few cases. Were Openreach to collapse the ~1000 headends to 200 it would make a lot of sense to do so more widely.

I suppose 200 is still quite a lot in the great scheme of things, if they are positioned nicely across the whole country.

I was just thinking how Zen are proposing having kit in all headends (I assume I'm understanding that right?) so that cached traffic doesn't need to waste capacity on their backhaul.  It seems a very logical thing to move as much of an ISP into the headends (including diverse local peering) as possible, rather than having a few points of failure/contention back to the ISP.

It was fascinating when I was on Digital Region with a friend on the same cabinet.  We could traceroute each other and it was as if the routing was done in the cabinet, though I assume it went to the exchange and back again?

[niemand]

Indeed. It depends how smart you want the kit at the exchanges to be. Switches are fine in many cases for right now as they just need to get the frames somewhere else. Having caching local means installing routers so it's very much about how abundant the backhaul out of the exchange is.

A reminder that Openreach charge for power and space so that does somewhat limit the kit you can colocate, however the fewer handover points there are the easier it is to rent dark fibre or lease wavelengths from them and use them to build diverse networks as you're more likely to have access to extensive metro and national networks letting a provider get to colo space and peering points relatively easily and closely to customers.

BT being obliged to sell dark fibre from some places helps a ton here, too. Renting DF and lighting it is probably going to be more efficient in many cases than putting smarter kit and caches into an exchange building.

Reaching the customers as I mentioned say 40 km for PON, 40-80 km range for the optics to the subtended cabinet. Allow some slack in the optical budget but as long as you can get a headend within say 100 km of fibre of the end users you're good to go.

[Alex Atkin UK]

Why did my brain automatically think co-location in the headend/exchange when you're right, if there is somewhere to peer with nearby then odds are its via a local data centre so you don't need the kit in the headend itself, just the fibre link and the diversity you're going to have from that data centre.

Its really fascinating to try to get my head around how an ISP network can actually be comprised, considering I can't even get VLAN tagging to work myself. 

The only time I saw ISP kit was when Plusnet were still at their original location in 2002 and I believe their whole peering were just two fibres coming into their data centre.  For all I know one was in, one was out, they never went into detail as it was just part of the tour as a new employee.

Presumably it was still fibre backhaul back then when most customers were still using 56K modems that I believe terminated at the exchange?

[niemand]

Actually dialup didn't terminate at the exchange. The signals were digitised and then sent along ISDN, potentially in bigger pipes still, to wherever they needed to go to reach the ISP's racks.

My employer purchased FRIACO from BT: calls to the FRIACO numbers were routed to us digitally where they were then demultiplexed back into individual calls, converted back to analogue and demodulated.

Yes - your digital data on dialup left your machine via DAC, digital to analogue, then ADC at the exchange, multiplexing onto a primary rate ISDN circuit for delivery to the ISP where it was demultiplexed, put through DAC, then ADC for the ones and zeroes to be fed to ongoing kit.

Same happened for non-FRIACO calls except that rather than the ISP buying the entire 32 channel primary rate ISDN bearer they went as normal calls so were billed per minute.