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Cant get more than 30Mbps on an 80/20

kitz
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Cant get more than 30Mbps on an 80/20

Ive recently been doing some testing on the TG582n after its been noticed that using parental control in this router slows speeds down dramatically and has a drastic effect on page loading time /DNS.    Ive commented on that thread here.

Today Ive devoted some time to testing my connection and no matter what I do, I cant achieve speeds of more than 28-30Mbps in a single thread.
Yes I can acheive speedtests of 72Mbps, but ONLY by using multiple threads.
During the testing process Ive used both the TG582n and a direct PPPoE connection to the modem.
Ive used a HG612 modem and also an ECI modem.
Ive also tested on another (xp) machine which is seeing the same thing.  Ive checked the speed of my LAN and files across the LAN have no problem attaining full speed.

JDs speedtester uses 2 threads and the most I can get is circa 60Mbps
TBB & speedtest.net use 6 and 4 threads respectively.  Using multi threading mode I can acheive 72Mbps.
Yet if I download a http file or ftp I can only get 28Mbps.

You can actually see on a TBB speedtest that a single thread will only attain 28-30Mbps

Ive always noticed the 28Mbps per thread since getting vdsl, yet I dont see this on speedtests by BT, sky nor Zen users.

Now I do a fair bit of FTP and if Im on a 80/20 product then I expect to get speeds of around 70Mbps to my server at least some of the time and not be restricted to 28Mbps max.
Not to mention the fact that I should be able to get it on http too. 
Ive attached a screen cap from last night showing a pretty dismal average of 18Mbps (upstream is fine) FTP speed.  Yet someone on a Zen connection can get an average of 70Mbps to the same server.
Why is this?
37 REPLIES 37
dvorak
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Re: Cant get more than 30Mbps on an 80/20

I certainly see something similar on FTP from my server too.
If I download 1 file it peaks at 2.4MB/s, 2 files simultaneously (using two threads) each will come down at 2.4MB/s.
I would expect the single file to maxing out the line, but it doesn't.
On the TBB test I don't see the same single threaded restriction as you though
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ejs
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Re: Cant get more than 30Mbps on an 80/20

Could XP need the TCP RWIN increased? More recent operating systems have auto-tuning networking stacks so wouldn't need tweaking.
SuperZoom
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Re: Cant get more than 30Mbps on an 80/20

I'm wondering this too. However, it may not be quite that simple.
Strangely enough, I've been puzzled by the exact opposite behaviour (also exhibited on XP)!
I can certainly get different ThinkBroadband speedtester results by booting the same machine into XP with a large, fixed RWIN of 1,045,440 bytes and MTU of 1492 bytes, compared to booting it into Linux with the 3.8 kernel and all default (auto-tuning) network settings.
Using the TBB graphical tester, in XP the single TBB protocol thread can max out the connection but the 6-thread HTTP test produces a result akin to congestion; whilst in Linux the single thread doesn't go above 50Mbps and it takes the 6 HTTP threads to show the speed you'd expect from the connection. I'm testing this on FTTP, so line speed is line speed, and that apparent 50Mbps single-thread ceiling in Linux is the same for an 80/20 connection and for a 100/15 connection, interestingly.
Nevertheless, there are other complicating factors when using graphical testers. CPU power and the combination of browser and flash version all matter. For example, on XP Chrome gives consistently worse results than Pale Moon in the TBB flash-based tester, I have found.
For that reason, I personally always test throughput using cURL and the 100MB zip file from ThinkBroadband - it works reliably on all OSs and hardware.
Using that measure, I see more or less the same throughput from XP and Linux (Linux is actually a tad lower because the RWIN takes a moment to ramp up) and a single HTTP port 80 thread can max out the connection in both cases.
As far as FTP goes, using some implementations of SSH can limit transfer speeds - although that may not be relevant.
Anyway, prompted by this thread, I had chance to do a series of tests this morning which may give you some more information to work with, Kitz. It could also get quite confusing, since I compared two different OSs, two routers, two separate FTTP connections and three browsers, so I'll split the results over 4 posts below in an attempt to make them more manageable.
Make of them what you will, but perhaps bear in mind that there is a further complicating factor. The results may well be showing "features" specific to my particular connection. I'm not too impressed with it generally in terms of responsiveness for general browsing: I think there may be congestion and/or switching/routing issues with the backhaul path. That's why I have both 80/20 and 100/15 FTTP variants to test currently. So it would be interesting to know whether anyone else can replicate the effects.
Either way, I hope it may provide a useful additional perspective to compare.
SuperZoom
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Re: Cant get more than 30Mbps on an 80/20

Usual Router - Windows XP
So these results are from a dual-boot laptop using wired ethernet.
It is only fast ethernet, although it is connected to a gigabit port on my router (which is not a Technicolor) via a separate gigabit switch.
I chose this setup so that in a subsequent test I could connect it directly to a fast ethernet port on a BT HomeHub 4 and show the same effect.
XP is configured to use an MTU of 1492 and an RWIN of 1045440.
The filenames show which FTTP connection and browser was used.
SuperZoom
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Re: Cant get more than 30Mbps on an 80/20

BT Home Hub 4 - Windows XP
Still in XP, but this time connected directly to the Home Hub 4. No separate switch and no gigabit ethernet components.
Network stack settings unchanged.
Again, the filenames show which FTTP connection speed and browser was used.
SuperZoom
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Re: Cant get more than 30Mbps on an 80/20

Usual Router - Linux
Back to my normal router and connected through the gigabit swtich, but this time booted into Linux Mint 15.
Network settings all default, including auto MTU, except for the extra test where I manually set the MTU to 1492 - which made no difference.
Once again, the filenames show which FTTP connection speed was used. I only tested the latest version of Firefox and flash on Linux though. There are limits to my dedication!
SuperZoom
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Re: Cant get more than 30Mbps on an 80/20

BT Home Hub 4 - Linux
And finally, the two FTTP connections each with the same Linux network settings but connected directly to a 100Mbps port (not the GigE one) on the HH4.
kitz
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Re: Cant get more than 30Mbps on an 80/20

Quote from: ejs
Could XP need the TCP RWIN increased? More recent operating systems have auto-tuning networking stacks so wouldn't need tweaking.

I'm on Win7.    I also tested with an XP machine which is the same.
Both machines dont display the same behaviour transferring across the LAN.  It appears to only occur with WAN traffic.
Ive also tested with PPPoE connections on an ECI and HG612 modem.  Ive tried not using my gigE network switch and also direct to the modem and/or router.
kitz
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Re: Cant get more than 30Mbps on an 80/20

Thanks for those results.    In a way its good to see Im not alone in this issue, but I really am stumped at what it could be.
The tests I carried out yesterday on the Win7 machine can be seen here.  
I didnt record any tests from the XP machine, just used it to confirm that it was also displaying the same behaviour and check that there was no problem with speeds on the LAN.

----
PS when googling I also came across someone else seemingly stuck with a similar issue of 28Mbps per thread link
w23
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Re: Cant get more than 30Mbps on an 80/20

Plusnet Unlimited FTTC with Fritz!Box 7390 syncing at 64 down / 20 up:

Avast 'shields' temporarily disabled otherwise the HTTP x6 result is 'all over the place'.
Wired test with Dell Vostro 1700 Laptop (Core 2 Duo 2.2GHz, 100Mbit Ethernet) & Windows Vista.
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SuperZoom
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Re: Cant get more than 30Mbps on an 80/20

Just to add the FTP angle to your picture, I captured a download from Debian's UK FTP server this morning on the 80/20 connection.
711,393,280 bytes in 83 seconds - so over 68Mbps as an average, and the attached time sequence graph shows it was very consistent.
That's a single thread using cURL in Windows (it can do FTP as well as HTTP).
I've definitely had much worse graphs than that for unencrypted FTP (often it would be all over the place whilst an SFTP download from the same server gave a nice straight line, suggesting a QoS profile issue,) so I'm pretty pleased with that benchmark for my connection.
If there is some kind of single thread limitation caused by PN's setup, therefore, it isn't PN-wide...
Since BT apply their own QoS, though, it is possible that there may be a setup error specific to your exchange I suppose.
The TBB graphs remain a bit of a puzzle to me...
The pfSense forum link wasn't that enlightening. His iPerf test in post #11 isn't comparing like with like because he isn't running the "WAN" link as PPPoE in test no.2 - it's just straightforward routing.
I got tired of being told that any problems I raised "must be" my router, so I set up my own local PPPoE concentrator back in July to benchmark what throughput it was capable of whilst processing the extra overhead of PPPoE on the WAN side. I found it can route at least 655Mbps over PPPoE, and I think that result was limited by the LAN-side client I used for the test, in fact; but it was good enough for me so I didn't bother to repeat it. I don't think PlusNet's Technicolor can quite match that though...  Wink
kitz
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Re: Cant get more than 30Mbps on an 80/20

Thanks for the input superzoom.    There has to be a solution for this somewhere.    Cry
Trawling the net I seem to have come across a few users being restricted to 28-30Mb speeds, but I cant get any useful info from this posts other than it may be a modem/router issue.
Has anyone got any ideas on this please.  Id appreciate some input from Plusnet reps too.  Is Tomo about, he normally has good ideas when it comes to stuff like this?
It seems to be on the WAN side only.  I dont appear to have any problems exceeding 30Mbps on my LAN.
Using PPPoE and testing with an ECI and a Huawei modem would also appear to rule out modem/router issue.
Just for the sake of elimination Ive also removed my Intel NIC and tried using my onboard LAN but that makes no difference either.
System is an i7 with a gigabyte z77-d3h running Win7 Pro.
atm whilst testing & trying to eliminate everything, Im running my network without the Netgear GigE network switch and going through the TG582n so currently limited to 10/100.
But you can see from the attached that the XP machine also can only get 30Mbps when downloading from the internet. [1]
Also attached is a screen cap proving that LAN traffic is NOT affected. [2]
SuperZoom
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Re: Cant get more than 30Mbps on an 80/20

Well, the only obvious link between Win7 and Linux is the auto-tuning network stack, so one quick and simple check would be to set up TCP on your XP machine (which isn't auto-tuning) with fixed settings which will definitely allow max throughput with a single thread and see whether that makes any difference.
A quick dive into DrTCP and a restart later you'll have one more piece of useful information.
I'd suggest an MTU of 1492 on your network card and the attached for the rest (since I've previously tested that to work on an XP machine). Best to check that the TG582n is also set to 1492 - some routers default to a lower value for PPPoE for reasons best known to their developers.
Would be really interesting to know the result.
It also isn't clear whether you've tried a direct PPPoE connection with the WinXP machine or only with the Win7 one - again, if nothing else, two different network stacks provides a fuller picture. Of course, XP will use an MTU of 1480 in that scenario, which you won't be able to change.
(According to TechNet, it's a value which Microsoft fixed to take into account the normal PPPoE header of 6 bytes, plus the largest possible outer PPP header of 4 bytes, plus the largest possible Multilink PPP header of another 4 bytes, plus the largest possible PPP header for compression and encryption (4 bytes), and the 2-byte PPP header that identifies the actual packet being sent - just to cover all possible circumstances.)
If none of that makes any difference then it either points to something WAN-side (whether PlusNet or BT responsible) or perhaps some factor common to all your machines like a favourite software firewall or some other configuration. That can be eliminated by borrowing a laptop from elsewhere known to exceed 30Mbps.
That's all I can think of for now without trying another router.
Oh, the LAN traffic is FTP / HTTP as well? If not, it might be an idea to test to make sure the issue isn't something to do with how quickly the application can retrieve the data from the TCP stack, or again something to do with a software firewall setting. Just a thought if nothing else provides an explanation. A Wireshark capture may give some helpful clues if it comes to that.
dave
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Re: Cant get more than 30Mbps on an 80/20

Hi kitz,
My instinct says the most likely candidates are MTU, latency or the modem. PPPoE has a maximum MTU of 1492 but depending on configuration 1480 does sometimes work better. What's the latency like on the connection?
Dave Tomlinson
Enterprise Architect - Network & OSS
Plusnet Technology