A problem on TCP in High RTT Environment.

[Niu Zhixiong]

I am sure that wnd is about 2MB all the time.
This is my latest capture, plz see Google Drive.
In the latest test, TCP(0s-120s) is about 9Mbps and SCTP(0s-120s) is about
18Mbps.
(The bandwidth(20Mbps) and delay(200ms) is set by dummynet)
The SCTP and TCP are tested in same environment.

​
 sctp.pcapng.gz
<https://docs.google.com/file/d/0By8sTL79ob4tYl9sM2V5a19iNVU/edit?usp=drive_web>
​​
 tcp.pcapng.gz
<https://docs.google.com/file/d/0By8sTL79ob4tV0NMR1FYLUQ3MWs/edit?usp=drive_web>
​



Regards,
Niu Zhixiong
－－－－－－－－－－－－－－－
 kaiaixi at gmail.com


On Sun, Aug 10, 2014 at 10:23 AM, John-Mark Gurney <jmg at funkthat.com> wrote:

> Niu Zhixiong wrote this message on Sun, Aug 10, 2014 at 10:12 +0800:
> > During the TCP4 transmission.
> > Proto Recv-Q Send-Q Local Address          Foreign Address        (state)
> > tcp4       0 2097346 10.0.10.2.13504        10.0.10.3.9000
> > ESTABLISHED
>
> Ok, so you are getting a full 2MB in there, and w/ that, you should
> easily be saturating your pipe...
>
> The next thing would be to get a tcpdump, and take a look at the
> window size.. Wireshark has lots of neat tools to make this analysis
> easy...  Another tool that is good is tcptrace..  It can output a
> variety of different graphs that will help you track down, and see
> what part of the system is the problem...
>
> You probably only need a few tens of seconds of the tcpdump...
>
> > On Sun, Aug 10, 2014 at 4:58 AM, Michael Tuexen <
> > Michael.Tuexen at lurchi.franken.de> wrote:
> >
> > >
> > > On 09 Aug 2014, at 22:45, John-Mark Gurney <jmg at funkthat.com> wrote:
> > >
> > > > Michael Tuexen wrote this message on Sat, Aug 09, 2014 at 21:51
> +0200:
> > > >>
> > > >> On 09 Aug 2014, at 20:42, John-Mark Gurney <jmg at funkthat.com>
> wrote:
> > > >>
> > > >>> Niu Zhixiong wrote this message on Fri, Aug 08, 2014 at 20:34
> +0800:
> > > >>>> Dear all,
> > > >>>>
> > > >>>> Last month, I send problems related to FTP/TCP in a high RTT
> > > environment.
> > > >>>> After that, I setup a simulation environment(Dummynet) to test TCP
> > > and SCTP
> > > >>>> in high delay environment. After finishing the test, I can see
> TCP is
> > > >>>> always slower than SCTP. But, I think it is not possible. (Plz
> see the
> > > >>>> figure in the attachment). When the delay is 200ms(means
> RTT=400ms).
> > > >>>> Besides, the TCP is extremely slow.
> > > >>>>
> > > >>>> ALL BW=20Mbps, DELAY= 0 ~ 200MS, Packet LOSS = 0 (by dummynet)
> > > >>>>
> > > >>>> This is my parameters:
> > > >>>> FreeBSD vfreetest0 10.0-RELEASE FreeBSD 10.0-RELEASE #0: Thu Aug
>  7
> > > >>>> 11:04:15 HKT 2014
> > > >>>>
> > > >>>> sysctl net.inet.tcp
> > > >>>
> > > >>> [...]
> > > >>>
> > > >>>> net.inet.tcp.recvbuf_auto: 0
> > > >>>
> > > >>> [...]
> > > >>>
> > > >>>> net.inet.tcp.sendbuf_auto: 0
> > > >>>
> > > >>> Try enabling this...  This should allow the buffer to grow large
> enough
> > > >>> to deal w/ the higher latency...
> > > >>>
> > > >>> Also, make sure your program isn't setting the recv buffer size as
> that
> > > >>> will disable the auto growing...
> > > >> I think the program sets the buffer to 2MB, which it also does for
> SCTP.
> > > >> So having both statically at the same size makes sense for the
> > > comparison.
> > > >> I remember that there was a bug in the combination of LRO and
> delayed
> > > ACK,
> > > >> which was fixed, but I don't remember it was fixed before 10.0...
> > > >
> > > > Sounds like disabling LRO and TSO would be a useful test to see if
> that
> > > > improves things...  But hiren said that the fix made it, so...
> > > >
> > > >>> If you use netstat -a, you should be able to see the send-q on the
> > > >>> sender grow as necessary...
> > > >
> > > > Also, getting the send-q output while it's running would let us know
> > > > if the buffer is getting to 2MB or not...
> > > That is correct. Niu: Can you provide this?
>
> --
>   John-Mark Gurney                              Voice: +1 415 225 5579
>
>      "All that I will do, has been done, All that I have, has not."
>