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Standard User voxmagna1
(newbie) Wed 21-Sep-16 21:45:38
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TBB testing: Check your PC first!

[link to this post]
I don't know if this is the right place to post this info and question. After I complained to my ISP that their Superfast speeds were only making 25mb/s tested with TBB and BTW, I was asked to do BTW speed tests every couple of hours and they would get the results within 48 hours from the BT server. Not an unreasonable response from the ISP.

I am supposed to be getting a Superfast(?) fibre service with the BT cabinet just across the road. My maximum line limit is 74Mb/S which I have seen before switching ISP and is confirmed as obtainable on the BT Infinity database . The BTW download speeds corresponded with TBB X6 speeds but were nowhere near the single thread download speed. In addition I resorted to a stopwatch to time TBB file downloads which were running at 250kB/S snail pace and nowhere near corrosponding to the single or multiple thread speeds.

One curious thing was the TBB speedometer would sail up to 25Mb/S (1/2 the expected) and sit there without any jitter even at peak useage times. To me that suggested something was rate limiting. I spent a day running the TBB and BTW speed tests getting similar results of 28-34 Mb/s on single thread downoads - flat lined and in the red for a sub standard BTW test. O.K so I thought I have the info now and a pretty good case to go back to the ISP with. Something kept niggling me. Why were the TBB single thread and X6 thread download speed so different? I had disabled background services for AV,Firewalls, VPN and Malware App. The TBB info kept saying I had AV running when it wasn't and there could be other problems which there were not, I had to treat the TBB 'advice' as potentially misleading.

I have 2 PC's on a 1Gb Ethernet home network - one runs an old Win XP SP3 (1Gb NIC), the other is very high end liquid cooled Win 7-64. The first test runs were on the fast Win7-64 PC. When I finished gathering results I did some further TBB speed tests on the XP box expecting it to be rubbish - It came back with speeds up to 65Mb/s on single thread!

I did a lot of Googling in the area of RWIN MTU. and therein is the problem. Apparently all Win OS systems up to Win7 do not automatically adjust the MTU parameters to optimize performance. On an enthusiast PC like mine, various websites had recommended parameter adjustments which I may have made in the past and probably not had any issues on slower ADSL connections up to 6Mb/S.

As a rule I don't use 'optimising' Apps as most are full of Adware, want money for fixes and don't easily uninstall. I broke my rule for TCPOptimizer.exe, ran it for Optimize option on the Win7-64 PC and couldn't believe what I saw. TBB single thread and X6 downloads were both a straight line at 72Mb/s and a 50mb test file download was at around 4Mb/Second.

I repeated the MTU optimize on the XP box and that got better too. Thinking this was a fluke, I had saved the old and new RWIN configurations and went back to the original config. TBB download speed came back at 30mb/s along with the other problems.

My situation could be similar to that which others may have with older PCs. when running running TBB and BTW tests, uploading them for others to see, complaining miserably to the ISP whilst venting my anger on Forums. I'm not saying my ISP doesn't have congestion or reliability issues, but knowing the device used to get performance results is ok is very important. I have been using Wireshark to explore downloads even further. My packet size is 1487 so add on +28 gives 1515 and the windows default of 1500 should be fine. Therefore the optimizing done by the app must be its choice of several RWIN parameters and I'm not clever enough to know about those yet!

I think there's another 'fly in the ointment' I need help with. After bashing away trying different configurations and MTU, doing ping tests for bad packets etc. I felt all was going bad to worse and couldn't get back the high download speeds I had achieved, despite using the same config file. It was late at night and congestion shouldn't have been an issue.

Then I did a power down/up reset on the ISP supplied Thomson router and all came back good and has stayed good.

Can anybody tell me if the stock ISP routers have learning capability by using bad packet transmissions then keep reducing throughput? When I had slow speeds on ADSL due to a long copper line length to the exchange, I had a timeswitch on their router which rebooted it once each day during the night.

I read an old post from somebody who replaced their XP box with Win7-64 PC and complained his download speeds were worse and nobody had the answer. I keep reminding myself that with these superfast broadband speeds, actual performance may be down to the NIC driver and OS configuration. With slower ADSL tweaking might win you +1/2Mb/s but with fast fibre I was losing 1/2 my download speed. In future I would try a couple of newish laptops before complaining or uploading bad results to my TBB profile.

The picture gets more complicated when you add in a layer of VPN working. The type of routing used by VPN may need a lower MTU setting. I read so many posts from users signed up to their VPN service saying they either couldn't get a connection or downloads were so slow the service was unuseable. It's always a good idea to look at the CPU loading during a download. My 6 core i7 sits at 1% and the old XP box is peaky at up to 20%, neither suggested problems due due to the CPU.

Having had this unhappy experience and fixed my slow download problem I wonder how many other older PC's are giving poor download speeds caused by their configuration? I now fully appreciate why a hardware dongle like SamKnows attached to the router is a better reference for speed testing, particularly if you are making a complaint to your ISP.
Standard User Michael_Chare
(experienced) Wed 21-Sep-16 23:41:46
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Re: TBB testing: Check your PC first!

[re: voxmagna1] [link to this post]
I have found that rebooting a PC just before running a test can help.

Michael Chare
Standard User legume
(experienced) Thu 22-Sep-16 19:51:19
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Re: TBB testing: Check your PC first!

[re: voxmagna1] [link to this post]
Long post!

Un-tweaked windows 7 for me is OK by default, so I guess it was tweaking that messed it up for you.

ISP routers won't limit at IP level based on errors.

" My packet size is 1487 so add on +28 gives 1515 and the windows default of 1500 should be fine."

Doesn't really make sense to me, not sure what test or wireshark output would give that.

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