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[Weaver]

If Virgin claims to deliver say 200 Mbps downstream, what happens if two users do a download simultaneously? What throughput does each user see?

I'm just wondering if 200Mbps translates into 2Mbps max per user if you have 100 users in your area all downloading from say Akamai at the same time because of Windows Update or such.

Is there any real chance of ever seeing anything even close to 200 Mbps unless for somehow th network is deserted? Or am I just completely misunderstanding?

[mrpops2ko]

No nothing like that. Think of each DSLAM / CTMS like big really fast modems split between many. I can't remember where I read it (or if these numbers are accurate) but each CTMS was rated for 3.6 gb/s DS and 600 mbit US. [these values probably aren't correct, i'm recalling from memory but it was a much higher DS allocation than US]

Thats the max throughput potentially. We don't know subscriber contention ratios, so you can't really work anything out. You'd start to experience congestion though if at peak times 16~ people were maxing their throughput for some reason. (which can happen in some circumstances, due to the 9-5 lifestyle and kids coming home around the same time all downloading from steam game servers etc)

When I was with VM, i'd see the full speed 24/7. Only recall 4-5 times where i'd seen congestion occur. VM have this cycle where they upgrade speeds and then play catch up with the network to handle throughput.

[Weaver]

That makes sense - it's not anywhere near as bad as it might sound to the ignoramus wot is me !
Many thanks

[Chrysalis]

the capacity is higher than 200mbit, but it isnt great, I think if I remember right what ignition posted its about 30-40% of capacity for top tier customers.  That to me is a quite a bad ratio and spells trouble for heavy take up areas.

Compare that to the much more favourable ratios on FTTC, with end users with a max possible 40/80mbit sharing 2.4gbit backhaul, also consider many lines dont sync at full speed making it even more favourable.

Sky also dont like selling 80mbit FTTC, so I expect their customers are mostly a mix of adsl and 40mbit FTTC, with their 10gbit exchange backhauls its a good contention ratio.

[Weaver]

How many punters are there sharing a particular pipe of size x on VM and on BT FTTC!

[guest]

When Virgin were punting 152Mbps as the top speed then the overall downstream bandwidth for that node/segment was 440Mbps with 50Mbps upstream. That could be shared (IIRC) between up to 32 customers with 3 customers being capable of totally saturating the downstream.

In addition not all areas of cable are equal - a lot of the area around Leics is still running docsis rather than eurodocsis (eurodocsis has higher downstream & upstream) and Cat-C resegmentation isn't likely to happen soon as the current wiring would shame even Kellys.

You takes your chances etc.....

[Weaver]

I wonder how many punters who are thinking about this service know that it might only be 13.75 Mbps d/s sometimes then, not 150 Mbps as advertised. The figures have so much variance behind them as to be completely useless, you never know from one minute to the next what you're going to get.

It seems very much a matter of where you are as well, from the experience of other posters.

<rant>
I only get 5.25 Mbps, but it pretty much never varies even slightly, unless there's some exceptional reason, such as an attack in progress. (I get people scanning my IPv4 range at a high rate, lots of TCP connection attempts per second, which can easily saturate my poor pipe and stop me watching Netflix, so I could do with setting up an ISP-end firewall in addition to my local one.) But my service never changes according to time of day. Even during the men's final of Wimbledon, the BBC iPlayer service held up 100% during the match so congrats to the BBC's content server farms and to A&A who I know bought extra capacity from BT well in advance. I pay for x and I get it, 100% of it. Can't imagine paying for a completely random, unpredictable, effectively unspecified service. </rant>

[Chrysalis]

yeah cable in leics is bad in just about every city area I have checked.  The only consistently good VM connection I have seen is just outside leics forest east.

[guest]

That's odd because the wiring there (LFE/Braunstone Crossroads) is 30 years old & was installed by LCL. The coax cable is the cheapest stuff you can imagine & I can't believe that it'll work with eurodocsis 3 frequencies, they had a hard enough time getting it to work with docsis 2.0

For anyone wondering - cable is very sensitive to the voltage levels presented to the CM. Docsis 3.0 will sometimes desync at around 8dBmV at the upper end (Virgin allow 10dBmV) and at the lower end there's some variability regarding increased codeword erroring. Installers will often have to put an inline attenuator in place as there's very limited attenuation tap points in most cabs.

Cable is not a panacea & has its own set of issues as its always used higher frequencies than xDSL. Some of those issues are going to affect g.fast more & it'll be interesting to see if Openreach technicians can cope with them on a day to day basis - I suspect not.

[Chrysalis]

it is possible the VM connection is just lucky with who else is on the node? (light users), the address is on kirby lane in kirby muxloe.