200M : Single thread/stream download problems

[downupload]

This is more of a call for input given a fairly specific problem myself and a bunch of other people, both local and those who've been posting on VM's own forums, have been unsuccessful in trying to get resolved. I'll try to be brief!

Basically, as the thread title says, performance of single-thread downloads is extremely poor, but because VM's only recognised diagnostic tool speedtest.net uses dozens of simultaneous network threads, it hides the problem, making it extremely difficult to get VM support to accept a problem and leading them to blame the Internet in general for not living up to their network's uber speeds.

Weirdly, this doesn't affect every website equally e.g. I found downloads from the Cachefly CDN and Virtualbox's website to be generally quite fast. Comparing traceroutes, they both seem to avoid going via London interconnection points; I'm not sure if that has anything to do with it.

But in general, I've found most single-thread downloads e.g. normal web browser downloads, to max at something like 10 megabits (I'm not confusing bits and bytes BTW), on a 200 megabits package.

About the simplest way of testing this is a decent speed tester like the one at thinkbroadband: http://www.thinkbroadband.com/speedt...01515763067203

Speedtest reports 200Mb/s on this connection so VM phone support refused to open a congestion ticket - forum staff agreed there's a problem and opened a ticket (well more than one actually) but they always get closed with no resolution.

Has anyone else here encountered this issue? There are some sizeable threads over on VM's forums discussing the issue. Run a TBB speed test if you're not sure.

Thanks!

[david_w2k]

I didn't know there was a difference until you posted this. I get 200 mbps on the multithread test... but 55-60 mbps on the single thread!

[downupload]

Thanks for checking! See, I think that's part of the problem - most people won't be aware of the difference and so won't be complaining about it (it took some digging for me to figure out what was going on when it got bad enough to cause real problems on a regular basis). Or, when people do notice poor file download speeds and try to complain, VM support will point them to speedtest.net and blame the website for the poor speed. Just, that doesn't wash when it's nearly *every* website that's affected, and those same websites perform just fine for other ISPs.

It does vary in severity and seems to depend what CMTS you're connected to. From the very limited sample size of people who've posted on the VM forum thread, most people affected seem to be on a CMTS with a MAC address owned by RiverDelta (a company acquired by Motorola), but recently at least one person has the same problem on a Cisco one. I've not seen anyone on an Arris CMTS affected yet, but again it's a very limited sample size so it's hard to be sure.

[Kabaal]

We're probably all affected by it to some degree or another but personally i don't find it an issue. I rarely download things through the browser these days and when i do it's usually just small files anyway.

Single threaded FTP downloads from my remote server come in at the full 100mbps of my connection nowadays so I can't really complain. In years past i'd usually only get around around 2-3MB/s with single threaded FTP to the same location.

If it's a big issue to someone there are plenty of download managers you can replace the default browser download with that will let you do segmented instead.

[david_w2k]

Originally Posted by downupload

Thanks for checking! See, I think that's part of the problem - most people won't be aware of the difference and so won't be complaining about it (it took some digging for me to figure out what was going on when it got bad enough to cause real problems on a regular basis). Or, when people do notice poor file download speeds and try to complain, VM support will point them to speedtest.net and blame the website for the poor speed. Just, that doesn't wash when it's nearly *every* website that's affected, and those same websites perform just fine for other ISPs.

It does vary in severity and seems to depend what CMTS you're connected to. From the very limited sample size of people who've posted on the VM forum thread, most people affected seem to be on a CMTS with a MAC address owned by RiverDelta (a company acquired by Motorola), but recently at least one person has the same problem on a Cisco one. I've not seen anyone on an Arris CMTS affected yet, but again it's a very limited sample size so it's hard to be sure.

Yeah that is really interesting - how do you get the MAC of your CMTS?

I do not know if I can face trying to explain this issue to Virgin first line support - sounds like you have a lot of patience ;-).

Any Virgin Media techs on here have any ideas?

EDIT - I haven't actually had any noticeable performance issues, I guess because I don't download files that often.

[downupload]

Originally Posted by Kabaal

We're probably all affected by it to some degree or another but personally i don't find it an issue. I rarely download things through the browser these days and when i do it's usually just small files anyway.

The problem is the single thread speed is drastically below the advertised speed, and browser downloads are far from the only thing affected - Windows Updates, PS4 game downloads, Streaming Youtube and Netflix, etc are all affected, and while download managers can alleviate the problem for some sites - many do not allow segmented downloads (Google Drive for example), and even with segments set to max it still doesn't achieve good speeds.

Originally Posted by david_w2k

Yeah that is really interesting - how do you get the MAC of your CMTS?

I do not know if I can face trying to explain this issue to Virgin first line support - sounds like you have a lot of patience ;-).

Any Virgin Media techs on here have any ideas?

EDIT - I haven't actually had any noticeable performance issues, I guess because I don't download files that often.

It depends on your modem/router setup. If you're using modem mode with your own router, the CMTS MAC address will be in the ARP table if you can access it. In router mode, I'm not sure if there's a way to find it on the SH2 but on the SH3 it is usually displayed on the logs page in the DHCP messages.

[Kabaal]

Originally Posted by downupload

The problem is the single thread speed is drastically below the advertised speed, and browser downloads are far from the only thing affected - Windows Updates, PS4 game downloads, Streaming Youtube and Netflix, etc are all affected, and while download managers can alleviate the problem for some sites - many do not allow segmented downloads (Google Drive for example), and even with segments set to max it still doesn't achieve good speeds.

Which is why i said I personally don't find it an issue.

Steam maxes my connection, Origin maxes it, Netflix and Amazon stream at the highest quality with no problems as does every other streaming service including YouTube, single threaded FTP downloads max me out. It's basically not an issue for anything i use other than the once in a blue moon i'm downloading something via the browser, and even then it only affects a percentage of those not all of them.

[downupload]

Oh I did forget to mention in the OP - it does seem area-related, some areas are completely unaffected, hence the point about it possibly being related to the CMTS. Locally, I know quite a few people on the same CMTS, both on the same line card and different line cards, all are affected equally, regardless of subscribed package. Since you're getting full speed over FTP you're most likely unaffected.

[General Maximus]

Originally Posted by david_w2k

I didn't know there was a difference until you posted this. I get 200 mbps on the multithread test... but 55-60 mbps on the single thread!

and that is why multithread downloads and multithread tests exist

[downupload]

Does anyone perhaps know a bit more about this? We've speculated it could be a combination of congestion and a poor choice of QoS system, and/or maybe something specific to a CMTS brand/chassis/firmware version for example. That doesn't quite explain why a handful of sites seem to mostly escape the problem, so maybe it's something deeper in the network (the unaffected sites seem to be local peering points rather than London, but there are only a few of them so it's hard to tell one way or another)? It's all just guesswork though given the lack of communication with VM on the matter.

In the affected areas it's bad enough to cause significant problems but although some VM forum staff keep trying to escalate the fault, we've gotten nowhere after ~a year of waiting.

Thanks!

[cje85]

I have this problem too. I'm on a Motorola CMTS which seem to be the most badly affected. The single thread speeds are very often below 50Mb now and are highly unstable, fluctuating up and down constantly.

One or two people on Cisco CMTS have reported it, but their single thread speeds appear to be much better and more stable.

Staff on the Virgin Media forum have escalated the fault to the network team on two occasions, but supposedly they haven't found any problem in spite of all the data provided and the growing number of complaints about single thread speeds.

I don't think there is anything more we as customers can do. A number of users on the VM forum have cancelled as a result of this issue, which is an option if an alternative service is available in your area. Other than that we can only hope this problem is resolved (or at least reduced) when the remaining Motorola systems are replaced.

[adduxi]

Yes, I've known about this for a good while, but it's never bothered me. I'm not a big downloader
My CMTS is River Delta, and I've never had anything over 30 with the single thread on Thinkbroadband, and I would get 212 on SpeedTest.

It may be a single channel on cable will never get 200 anyway? Is this not why we have 12 or 16 channels ?

[cje85]

Originally Posted by adduxi

Yes, I've known about this for a good while, but it's never bothered me. I'm not a big downloader
My CMTS is River Delta, and I've never had anything over 30 with the single thread on Thinkbroadband, and I would get 212 on SpeedTest.

It may be a single channel on cable will never get 200 anyway? Is this not why we have 12 or 16 channels ?

The number of channels isn't the same as the amount of download threads, it used to be possible (and still is for some) to achieve full 200Mb speeds on single thread downloads over 8 channels. Here's a test showing a perfect VM connection, achieving full speed on single and multi-thread.

http://www.thinkbroadband.com/speedt...3612785695.png

[watercooled]

Yeah as cje85 says it's not related to the number of DOCSIS channels, I myself used to get the full 100Mb throughput on a 100Mb package when a single channel would be limited to something like 55Mbps.

It's not just a case of complaining for the sake of complaining though; were I getting half or even a quarter of the sold speed it wouldn't be so bad, but when you're getting worse than ADSL2 performance for the majority of real-world downloads and having to wait substantially longer for things like software patches and GPU drivers and FTP transfers it's getting a bit silly. Same goes for VPN performance. As you can see on my TBB test, it's now as bad as 9Mbps and it's getting worse.

Even using a download manager for sites that support it didn't approach 200Mbps, and the single-thread performance seems to be the same regardless of package, so what's the point in paying for one of the higher tier packages unless you can make use of primarily highly threaded downloads?

Rant over, I was just hoping someone on this forum e.g. VM employee/network engineer might recognise what's going on and give us an idea of when it might get fixed.

[david_w2k]

Agreed, it would be great to hear from someone who has some further info.

Until I saw this thread I always assumed slow downloads and work vpn connection were due to throttling at the hosting side...

I have now also tested downloading multiple files at the same time, they max at the single thread speed, but the total download speed across all of them equals the full 200-220 megabits