Subject: Re: writing to channel limited to 2 Mb?

Re: writing to channel limited to 2 Mb?

From: Daniel Stenberg <>
Date: Wed, 10 Aug 2011 22:49:13 +0200 (CEST)

On Wed, 10 Aug 2011, Przemys³aw Szczygielski wrote:

> OK, so one last question. As I am not very fluent with SSH terminology, I am
> sure you would be able to answer me without digging into docs. Is it
> possible that my problem is because "The default session window in OpenSSH
> is 2MB already."?

Not really.

In SSH, each channel tells the other side a window with how much data that it
can accept. You then know how much data you can send to the other side. In
typical scenarios the other side then send updates to the window along the way
to inform that it is ready to receive more data.

In order to reach a good flow and transfer speed, you never let the window
size reach zero. Of course there might still be cases where you really cannot
accept more data for the moment and then you tell the other side to not send
more by setting the window to 0.

If the default window size is 2MB then each channel by default will accept 2MB
of data, but that doesn't say what it does with the window once the transfer
is in progress.


Received on 2011-08-10