A problem on TCP in High RTT Environment.

[John-Mark Gurney]

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."