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84 posts

Master Geek
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Topic # 115734 4-Apr-2013 20:34
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I have sent an email to through the online customer site, but I was wondering if anyone here had some ideas while I wait for them to get back to me.

It seems that there is a per TCP connection speed limit on Cable. I have a box at Linode in London and when transferring files via SSH the rate is slow ~200kB/s. First I thought it was just a slow route, but if I start two SSH session, running in side by side, I can have two parallel downloads each running at the ~200kB/s speed, so they are summing to something nearer ~400kB/s. Why can't I get ~400kB/s in the one connection when I can pull that cumulatively over two separate SSH sessions?

I can demo this as Linode has a speed test page that give you a file download https://www.linode.com/speedtest/

Using wget I can get http://speedtest.london.linode.com/100MB-london.bin in 9m 13s the file is 104857600B so average is 185kB/s

Then using wget in two separate terminals in parallel (I added ?1 and ?2 to the end of each URL so it didn't come from the transparent proxy) and I got 9m 44s for 175kB/s and 9m 45s for 175kB/s. If it was a bandwidth constrained connection I would have expected something like 19m 30s to complete the 200MB, but that is not the case.

Trying some of the other Linode speed test files I get the same results for Japan and Fremont. The speed is different but there seems to be a per connection limit and running in parallel doesn't seem to affect other download.

This isn't an issue at the Linode end as I pull the same file down to a box in the US 1m 40s 1MB/s so the Linode end can spit the content out fast enough on its speed test files.

So is there a per connection limit? Is there anyway to work around this so I can just have the one connection operating at full speed?

Thanks

Traceroute for completeness
<snip>:~$ traceroute speedtest.london.linode.com
traceroute to speedtest.london.linode.com (176.58.107.39), 30 hops max, 60 byte packets
 1  <snip>  0.591 ms  0.579 ms  0.725 ms
 2  * * *
 3  lo0.internet.ivpn.pe25.telstraclear.net (218.101.61.124)  67.656 ms  67.729 ms  67.711 ms
 4  ie2-g-0-0-0.telstraclear.net (203.98.50.2)  68.069 ms  68.070 ms  68.066 ms
 5  * * *
 6  unknown.telstraglobal.net (134.159.174.37)  68.177 ms  65.703 ms  65.807 ms
 7  i-0-0-4-0.tlot-core01.bx.telstraglobal.net (202.84.142.118)  156.907 ms  242.681 ms  243.022 ms
 8  i-0-0-0-3.eqla01.bi.telstraglobal.net (202.40.149.134)  242.474 ms  241.824 ms  241.969 ms
 9  63-218-51-149.static.pccwglobal.net (63.218.51.149)  283.869 ms  283.768 ms  283.598 ms
10  telecity.ge9-9.br02.ldn01.pccwbtn.net (63.218.13.222)  438.956 ms  394.823 ms  422.172 ms
11  212.111.33.238 (212.111.33.238)  422.297 ms  422.202 ms  422.249 ms
12  speedtest.london.linode.com (176.58.107.39)  421.653 ms  411.505 ms  411.487 ms

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BDFL - Memuneh
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  Reply # 793478 4-Apr-2013 20:35
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There was a loooong discussion about something similar here.

I don't remember reading the end of it. Go there and spend some time through it. Lots of good information.






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  Reply # 793565 4-Apr-2013 22:26
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freitasm: There was a loooong discussion about something similar here.

I don't remember reading the end of it. Go there and spend some time through it. Lots of good information.


Thanks there doesn't really seem to be an answer there other than some quirks in the TC network and upstreams. Odd that they still haven't fixed it given over a year and reproduction case is easy. Maybe the VF techs will have better luck?

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  Reply # 793567 4-Apr-2013 22:29
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karit:

Thanks there doesn't really seem to be an answer there other than some quirks in the TC network and upstreams. Odd that they still haven't fixed it given over a year and reproduction case is easy. Maybe the VF techs will have better luck?


'fix' would suggest that it's considered a bug rather than a feature.






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  Reply # 793581 4-Apr-2013 22:40
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DonGould:
karit:

Thanks there doesn't really seem to be an answer there other than some quirks in the TC network and upstreams. Odd that they still haven't fixed it given over a year and reproduction case is easy. Maybe the VF techs will have better luck?


'fix' would suggest that it's considered a bug rather than a feature.




If it si a feature can VF give us the reasoning why?

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  Reply # 793640 5-Apr-2013 01:14
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Long standing issue with Telstraclear's upstream/international providers (eg: TelstraGlobal etc).

At some point Vodafone will likely change cable customers to use their upstream providers (Vocus etc) instead of TelstraGlobal and problem will likely be resolved.

No idea when that will happen, maybe JohnR can comment?



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  Reply # 794897 8-Apr-2013 11:08
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Well got the "we'll look into this and get back to you if we require more information" response. So now to wait and see what happens.

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  Reply # 794908 8-Apr-2013 11:40
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"Long standing issue with Telstraclear's upstream/international providers (eg: TelstraGlobal etc). "

I don't think its a problem with TelstraGlobal at all. Testing from someplace else in NZ which goes thru TelstraGlobal I can download at 3MB/s quite easily (With 1 single TCP Connection) with no Caching.



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  Reply # 794913 8-Apr-2013 11:43
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Have you compared this speed to ssh/etc via a different NZ provider?

TCP speeds are affected by latency and TCP tuning at both ends of the connection.  TCP performanceover high bandwidth-delay product links (i.e. fast but high latency) is not brilliant, this is one of the many reasons why CDNs are so popular, as they cut down on the latency part of the equation.



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  Reply # 794918 8-Apr-2013 11:49
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deadlyllama: Have you compared this speed to ssh/etc via a different NZ provider?

TCP speeds are affected by latency and TCP tuning at both ends of the connection.  TCP performance over high bandwidth-delay product links (i.e. fast but high latency) is not brilliant, this is one of the many reasons why CDNs are so popular, as they cut down on the latency part of the equation.


Me no not yet. Though the the old thread, from Sep 2011, that was quoted about had done that research and Telstra Cable was performing worse than other ISPs. I will talk to friend and see if they can do my reproduction case (as in first post via the HTTP files) on a different ISP.



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  Reply # 799401 15-Apr-2013 08:38
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Have had some email discussions with VF on this, their network people are looking into this.

Over the weekend I did do a test on someones Telcom ADSL2+ connection and I was seeing about 4x the speed (~800kBps) and 50ms less latency (~350ms) on the Telecom connection. It was also behaving as a constrained pipe in that if you ran two downloads in parallel the overall speed was about the same but the per download speed was about half.

So it is possible to ship the data from the other side of the world faster than Cable currently does. Here hopes the VF network can track it down and sort it out once and for all :)



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  Reply # 805422 25-Apr-2013 12:47
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They have said they have replicated the issue on their cable test kit and the issue is not it their network. Their network team are apparently working with their upstreams, so we wait and see if/when it will get fixed.

BDFL - Memuneh
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  Reply # 805426 25-Apr-2013 12:52
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  Reply # 805433 25-Apr-2013 13:09
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karit: They have said they have replicated the issue on their cable test kit and the issue is not it their network. Their network team are apparently working with their upstreams, so we wait and see if/when it will get fixed.


Is it really a fault or by design?

I limit per connection rates on my servers to balance resource and hopefully reduce D/DoS involvement.






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  Reply # 805546 25-Apr-2013 18:40
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freitasm: So it took Vodafone buying the whole company to get someone to look at this then?



Yep.

Telstraclear didn't exactly have a great record for fixing known problems..like the time it took over 6 months to resolve their abysmal youtube performance or the 12 months it took them to resolve routes to gaming servers in Australia and many other examples in the past.






BDFL - Memuneh
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  Reply # 805552 25-Apr-2013 18:51
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It actually took even longer, nine months, to fix the YouTube problem, which was solved when they agreed to have the Google cache installed.




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