Date: Sat, 9 Aug 2014 11:42:32 -0700 From: John-Mark Gurney <jmg@funkthat.com> To: Niu Zhixiong <kaiaixi@gmail.com> Cc: freebsd-net@freebsd.org, Bill Yuan <bycn82@gmail.com> Subject: Re: A problem on TCP in High RTT Environment. Message-ID: <20140809184232.GF83475@funkthat.com> In-Reply-To: <CAOENNMA_CiBDJc0kchzUbTcf_JBwTJPF=PdBAUB6FPo-KzYkeQ@mail.gmail.com> References: <CAOENNMA_CiBDJc0kchzUbTcf_JBwTJPF=PdBAUB6FPo-KzYkeQ@mail.gmail.com>
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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...
If you use netstat -a, you should be able to see the send-q on the
sender grow as necessary...
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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