Upstream utilisation/ downstream utilisation - which is which?

[Retrovertigo]

Sorry for sounding a bit glum, but wanted to know which is which when it comes to download speeds.

Following on from my well documented speed woes, tech support are now giving me the runaround again.

For the past few months they have been saying my speed problems are down to downstream utilisation issues on the UBR I am on (and also confirmed by the area manager)

However, when I contacted tech support again (via the newsgroups) for an update, they are now saying I am not on the UBR that has downstream issues. Instead, they have decided my problem is now an upstream issue.

Rather conveniently for them, this means the slate is wiped clean with my waiting for the old problem to be fixed, and my "new" problem has been passed on the the relevant team. All rather handy from VM's perspective.

But which is which, and which is easier to fix? Or are they both sides of the same coin, and in fact are just as difficult to sort as each other?

It seems clear they are just going to keep throwing problems my way. Seems very strange tech can say they are looking at my modem, seeing me be on a busy UBR, then a few months later, decided I'm not on that UBR at all :/ Thanks

I should add that at this time of day I normally experience normal speeds. But I'm currently looking at a speed of 5meg off the newsgroups, and it is only 11:30 :(

[Ignitionnet]

Upstream 'issue' or upstream utilisation?

With the new overlay network both are possible to fix, depending on if you're already on the new platform (your downstream frequency will tell you this) and what modulation is being used upstream (your upstream info will tell you this).

[Retrovertigo]

They said it was upstream utilisation.

However, following a phonecall just now, I am switching to 50meg. I can't stand it any longer. I need decent speeds if only for using xbox live with no lag of an evening. It has been highly annoying having Forza 3 and Modern Warfare 2 sat here and not been able to play because of lag. So I've bitten the bullet.

[Sephiroth]

Upstream 'issue' or upstream utilisation?

With the new overlay network both are possible to fix, depending on if you're already on the new platform (your downstream frequency will tell you this) and what modulation is being used upstream (your upstream info will tell you this).

BB, it would be helpful if you could provide a table of frequencies and what they mean to someone trying to decipher them and investigate a problem.

Likewise the maning of the modulation - which some of us understand but which others would be keen to learn.

Cheers

---------- Post added at 12:36 ---------- Previous post was at 12:33 ----------

They said it was upstream utilisation.

However, following a phonecall just now, I am switching to 50meg. I can't stand it any longer. I need decent speeds if only for using xbox live with no lag of an evening. It has been highly annoying having Forza 3 and Modern Warfare 2 sat here and not been able to play because of lag. So I've bitten the bullet.
I'm not sure that 50 Mbps will per se help. The bit of luck you should hope to have is that your 50 Mbps circuit does not suffer from serious contention. If it does, then your game packets will be subject to discard and lag will remain a problem.

You could ask VM what the contention is in your area. They do know and some persistence might get you an answer to that question.

[caph]

I'm not sure that 50 Mbps will per se help. The bit of luck you should hope to have is that your 50 Mbps circuit does not suffer from serious contention. If it does, then your game packets will be subject to discard and lag will remain a problem.

You could ask VM what the contention is in your area. They do know and some persistence might get you an answer to that question.

Seph, as far as I've seen/heard there have been no reports at all of oversubscription by anyone on 50Mb. Have you heard of any? There are unfortunately a load of other problems with 50Mb that we seem to read about with alarming regularity and for that reason I would also say that 50Mb will not help per se.

Retro, it might be worth using the "Connection" link on this page to find out which UBR you are on for future reference, then you'll know if and when you get moved. It can save you time in diagnosing problems you experience in the future.

[Sephiroth]

Caph - I think we can deduce from a large number of 50 Mbps reports on this forum, particularly from the Manchester area, where contention is a very clear problem.

Although I never mentioned oversubscription, you might be right in a narrower sense that oversubscription hasn't occurred at least at the point where VM entered into contracts with customers (after all VM don't know what the customers will be doing). Thereafter the area is open to contention.

I still believe that, excepting bad circuitry, dropped lines are principally a contention issue.

[Ignitionnet]

If OP isn't on the overlay network already 50Mbps should resolve the congestion problem.

Contention is not a cause of connection drops except in the most extreme cases of upstream congestion.

[Ignitionnet]

Anyway..

3 things decide how much upstream bandwidth (bandwidth from customer's modem to Virgin Media) there is available to a particular area:

1) How many upstream channels are in use.
2) How wide these upstreams are.
3) How dense these upstreams are.

1 and 2 go together. Under the USA standards there's an RF (http://en.wikipedia.org/wiki/Radio_frequency) band available to upstream traffic between 5 and 40MHz giving a total theoretical RF bandwidth available of 35Mhz. On networks fully built to European standards, EuroDOCSIS this increases to 5 - 65MHz giving theoretically 60MHz. However it's not the case that all this bandwidth will be available, simply due to noise on the network. Baby monitors, pagers, power supply interference, many reasons can cause noise spikes on a network meaning that upstream channels have to be placed around them. In addition some networks don't have optics that can handle too many channels so how heavily these optics are being loaded also has to be a consideration.

Modems at the moment can only use 1 upstream channel at a time. Modems are load balanced between however many channels there are to try and spread load evenly, hence why number of channels is also an issue.

Channel width is a big part of bandwidth. How wide a channel is decides how many symbols it can carry per second, these symbols carry data as follows:

Channel Width 800kHz (0.8MHz) = Symbol Rate 640ksym/s (640 thousand symbols per second)
Channel Width 1.6MHz = Symbol Rate 1.28Msym/s (1.28 million symbols per second)
Channel Width 3.2MHz = Symbol Rate 2.56Msym/s
Channel Width 6.4MHz = Symbol Rate 5.12Msym/s

Increasing the width of a channel leaves it more vulnerable to noise, there's more of it to be interfered with, and in addition in some cases it lowers the quality and strength of the signal coming from the modem as well.

Density, this is how much data each symbol carries and is decided by the modulation being used. This runs as follows:

QPSK = 2 bits per symbol
8QAM = 3 bits per symbol
16QAM = 4 bits per symbol
32QAM = 5 bits per symbol
64QAM = 6 bits per symbol

Better quality networks and better quality signals (higher SNR) are required as you work up the chain of modulations / densities, QPSK will run as low as 12dB while 64QAM will be wanting closer to 27dB to run without severe issues.

There are 4 DOCSIS standards relevant to upstream, 1.0, 1.1, 2.0 and 3.0. 8, 32 and 64QAM and 6.4MHz wide channels are available to networks running in DOCSIS 2 or DOCSIS 3 mode only.

Apart from trial areas Virgin Media run DOCSIS 1.0 and 1.1 upstreams only which limits them to the following which can be seen running on the network right now:

1.6MHz 16QAM = 1.28 million (symbol rate for a 1.6MHz channel) * 4 (bits per symbol on the modulation 16QAM) = 5.12Mbit/s per channel (rare)
3.2MHz QPSK = 2.56 million * 2 = 5.12Mbit/s per channel
3.2MHz 16QAM = 2.56 million * 4 = 10.24Mbit/s per channel

The aim of most cable companies is to move to either 6.4MHz 64QAM or at least 3.2MHz 64QAM, this will likely be what is being used in the Huddersfield trial:

3.2MHz 64QAM = 15.36Mbit/s per channel
6.4MHz 64QAM = 30.72Mbit/s per channel

https://www.cableforum.co.uk/images/local/2009/11/14.gif

The amount of upstream channels available decides the total bandwidth and how many modems can run, the amount of bandwidth on each channel both has an influence on total number of modems as a higher bandwidth channel can handle more modems than 2 smaller channels even if they add up to the same bandwidth due to some statistical gubbins and also strongly influences how much bandwidth can be provisioned to each customer, IE how phat your upload speeds are!

In the future there will also be the capability to bond upstream channels. In the same way that the current DOCSIS 2 series is delivered by up to 4 channels of about 50Mbit/s each bonded together cable companies will be able to bond upstreams. When this happens you'll probably see a number of them using 3.2MHz wide 64QAM channels bonded together as they are so much more forgiving of bad networks than 6.4MHz 64QAM, however for all cable companies with DOCSIS 3 networks the 'gold standard' is to bond 4 6.4MHz 64QAM channels together:

4 x 6.4MHz 64QAM = 4 x 30.72Mbit/s = 122.88Mbit/s

Errors and omissions excepted, this was typed fairly quickly and in a rush.

[Retrovertigo]

I have had a message on the newsgroups that the migration in my area is now complete and speeds should be back to normal (Fallowfield, Manchester)

But this contradicts what the news team told me only yesterday morning, as far as I can tell. They gave me a new ref number and then an hour or so later are telling me work is done.

Speeds are worse than they have ever been. I tried last night at 3am and again this morning at 10am, and couldn't even manage 10meg.

To make matters worse, something that was being done to help me, has so far not happened. I was supposed to have been called by someone yesterday and today is almost over and no phonecall.

It kind of feels like I'm just being told whatever they need to, in order to put off actually letting me know they aren't willing to do anything.

[Ignitionnet]

Yes, well, arse and elbow come to mind when it comes to Virgin communicating internally.