In reply to a post by WWWombat:

That's perfectly reasonable when you look at averages - especially at 1 Mbps per user.

It's still a bit worrying that only 3 users - out of hundreds - can saturate things.

It is but it generally works fine. It probably won't be more than 200 - 250 users and remembering that VM's top product has the lowest uptake of the product set the maths get more and more sane as you go.

Saturating 300Mb for any length of time isn't something that most do

Plenty of operators have been selling 300Mb+ on just over 600Mb of capacity with largely okay results, Virgin sold 100Mb on 152Mb in some areas without too much pain, small nodes.

Virgin's tests in Cardiff have been a good example of this - the areas in Cardiff have access to 800Mb however individual modems only have access to 400Mb of this, but it seems to be working even though it's far from ideal.

In reply to a post by Ignitionnet:

It is but it generally works fine. It probably won't be more than 200 - 250 users and remembering that VM's top product has the lowest uptake of the product set the maths get more and more sane as you go.

True - less than 20% takeup of the 100Mbps+ tiers will indeed make the maths more sane.

It raises a question as to what speed packages BT would intend to put over the G.fast nodes. Having lower packages will change the equation there too.

Saturating 300Mb for any length of time isn't something that most do

Also true. I take your point about the effect seeding has on upstream though. I can imagine that has a greater impact, both percentage-wise and overall duration.

Plenty of operators have been selling 300Mb+ on just over 600Mb of capacity with largely okay results, Virgin sold 100Mb on 152Mb in some areas without too much pain, small nodes.

I wonder how far BT will push it. Will they even endure a "little pain"?

Virgin's tests in Cardiff have been a good example of this - the areas in Cardiff have access to 800Mb however individual modems only have access to 400Mb of this, but it seems to be working even though it's far from ideal.

Interesting. How does the 800 get split? 2 distinct banks of 400? Or each modem randomly gets assigned 8 out of 16 possible channels?

In reply to a post by WWWombat:

Interesting. How does the 800 get split? 2 distinct banks of 400? Or each modem randomly gets assigned 8 out of 16 possible channels?

Usually load balanced into a pre-configured bank of 400, say a group on channel ID 1-8, another channel ID 9-16 and a last one 5-12 however vendors can implement as they please.

In reply to a post by Ignitionnet:

There's no CWDM splitter in the cabinets as far as I'm aware. They run on point to point Ethernet backhaul over a single fibre from what I gather which each connection running on a dedicated fibre, 1000Base BX-10. A CWDM splitter is not required to run GPON and XGPON on the same fibre. To backhaul the cabinets with XGPON requires new line cards as the existing ones do not support it.

Answered my own question.

There are CWDM muxes in some cabinets, however this is not the case for the vast majority. Where there are restrictions on deploying new fibre there's sometimes a 'parent' cabinet which takes a single fibre from the headend and feeds child cabinets via the different colours.

This is in no way related to PON of any kind. PON doesn't need CWDM, the kit is there because the cabinets are expecting point to point Ethernet, PON ensures they get what they expect. Were PON in use there would be simple passive splitters, not a powered multiplexer.

Every day is a school day.

Edited by deleted (Wed 09-Sep-15 14:25:36)

I am hearing words like "some areas" "largely ok" instead of "perfect".

I think VM are a bad example to say it works because it seems congested everywhere I look round here I see them as an example of failure not success. I know people first hand who get under 20mbps every evening e.g. on a 150mbit package. VM is ok if you pretend the bad areas dont exist.

On a national average people tend to not max out that sort of bandwidth you are right, but when you analyse things locally, you might e.g. have 10 people on one street doing what you said mirroring a news group or downloading every 4k torrent they can get their hand on. I do know a few people who seem "addicted" to downloading all the time.

I think 300mbit on 1 gigabit shared would work if policed, so e.g. if the unused capacity drops below 20% or 10% then police the downstream on users to drop the utilisation, this keeps latency and packet loss at proper levels, then I am ok with it.

Whilst if its left as a free for all I forsee problems. I do suspect openreach do have policing policies in place on cabinets which is why they quote prioritized speeds?

I cannot see myself ordering g.fast based on what I am hearing, I prefer 80mbit on shared 2.5gbit to 300mbit shared on gigabit. There is a reason openreach have no cabinet backhaul congestion, they got the contention levels right. Also I think they will be pushing for 500mbit at some point on g.fast and also trying to push for higher density nodes?

Edited by Chrysalis (Wed 09-Sep-15 14:34:29)

In reply to a post by Chrysalis:

I prefer 80mbit on shared 2.5gbit to 300mbit shared on gigabit. There is a reason openreach have no cabinet backhaul congestion, they got the contention levels right. Also I think they will be pushing for 500mbit at some point on g.fast and also trying to push for higher density nodes?

G.fast has a 'prioritised' rate of 80Mb.

Under congestion conditions it'll perform better than FTTC, it has far more bandwidth per subscriber and people don't suddenly start downloading the Internet when their speeds go up. The jump from 80Mb to 300Mb is far smaller, functionality wise, than for example the one I had from 1.3Mb to 60Mb.

300Mb on 1Gb will work fine regardless of policing until such a time when usage per subscriber rises dramatically. Right now it averages sub-1Mb/s per modem on FTTC. If super-busy areas are going enough to congest with 80Mb prioritised rate it's probably best to let them get on with it rather than trying to deliver 3-figures Mb/s per modem to deliver a congestion free service.

there may be higher "potential" speeds under congestion, but latency and packet loss is what I am referring to which happens when a host link gets full, these then can have unpredictable affects on traffic.

How often do you see "acceptable" levels of congestion? I only tend to see "acceptable" levels when policing is carried out. Sadly once congestion starts to occur things can go downhill very fast when is no policing system in place.

Is burst speed more important than everything else

You have to look past the averages, peak time demand is more important. Of course we will disagree on VM, I seen them as a failure in capacity management whilst you dont.

If we look past the people who download the internet (which I think is a fair few of them around me), the typical user's increase will probably come from with what they can get away with so e.g. in the past it may be the case the bill payer would ban kids from downloading in the evening so his/her netflix/iplayer works properly, but lets them rip over night, something like g.fast may stop households needing to do that kind of thing so as such peak time demand jumps up. It may also be we see 4k streaming become more popular (which is inevitable, youtube and netflix already involved in 4k streaming) this ultimately increases bandwidth consumption, we are also in an era where games distribution is fast moving to digital on consoles, things dont stay stagnated as you are suggesting, and if this is how isp's approach things its no wonder they keep getting caught out, you said it yourself both VM and BT have been caught out by utilisation at different points of time.

Where I agree with you is if there is only typical users on a node, there wont be a problem, that I am not arguing. The problem is if there is a bunch of people insisting on getting the max out of their connection clustered together on one node, then we have a problem without policing or extra capacity. I think this is especially possible when you have crowded households where can be easily 4 to 5 devices downloading at the same time. As it wont be that easy for a single device to pull 300mbit+ but quite easy for a few to do it.

So as i said I will keep my VDSL line maybe I will claw crosstalk back also if people hop onto the g.fast service.

Edited by Chrysalis (Wed 09-Sep-15 20:30:58)