[erlang-questions] gen_sctp throughput mystery

[Johannes Govaerts]

Hi, 

Today I stumbled also across this issue. It turned out that you get
this behavior when not specifying the recbuf option at the server. The
default recbuf is only 1500 bytes. So when the client sends a package
he waits for acknowledgment before sending a another package; and at
the other side the server receives only one package and will only
acknowledge when sacktimeout is triggered because he never receives a
second package...

When using a higher recbuf value there is no throughput issue anymore.

Regards,
Johannes

On Tue, 6 Mar 2012 11:46:34 +0100
ext Raimo Niskanen <raimo+erlang-questions@REDACTED> wrote:

> On Sun, Mar 04, 2012 at 01:19:00PM +1100, Anthony Shipman wrote:
> > On Sun, 4 Mar 2012 12:43:49 pm Anthony Shipman wrote:
> > > > The now() value shows the packets being written to the socket
> > > > at 11ms intervals on the client but they are received at strict
> > > > 200ms intervals on the server. The server is just doing a
> > > > simple receive loop.
> > > >
> > > > Is there something in SCTP that limits the rate on an SCTP
> > > > stream?
> > > 
> > > I forgot to mention that the behaviour is the same for
> > > sctp_nodelay=true.
> > > 
> > 
> > Replying to my own question. It's the net.sctp.sack_timeout = 200
> > kernel parameter. But I don't understand why it should limit the
> > server to 5 packets per second over a localhost link.
> 
> Great finding if true... Can you elaborate? What happens when you
> tweak this parameter? Note that 1 / 200ms is exactly 5 per second.
> 
> I found this link:
>   http://sandarenu.blogspot.com/2009/11/reducing-time-between-sctp-message.html
> And a quote from it it says:
>   That 200ms is a configuration based on the SCTP RFC. According to
> that an acknowledgment(SACK) should be generated for at least every
> second packet received, and SHOULD be generated within 200 ms of the
> arrival of any unacknowledged DATA chunk.
> So, might it be so that if you send just one data chunk there will be
> a 200 ms delay before an ack?
> 
> I have focused on the SCTP socket API, not dug into the RFC:s...
> 
> > 
> > -- 
> > Anthony Shipman                    Mamas don't let your babies 
> > als@REDACTED                   grow up to be outsourced.
> > _______________________________________________
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> > erlang-questions@REDACTED
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> 


-- 
Johannes Govaerts
Nokia Siemens Networks 
phone: +32 473 36 65 28 
mailto: johannes.govaerts@REDACTED