Ticket #16 (closed defect)

Opened 11 years ago

Last modified 10 years ago

Slow Transfer Speeds

Reported by: anonymous Owned by:
Priority: normal Milestone:
Component: Version:
Keywords: Cc: bagder
Blocked By: Blocks:

Description

Hi.

Using ssh on high-speed internet links can see poor
performance with TCP Window size adjustments.

For openssh, there is a workaround for this slow speed,
which increases the window size inside of the channel:

If you are using openssh-3.5pl, the line to change is
119 of channels.h. Change value of
CHAN_SES_WINDOW_DEFAULT from 4*CHAN_SES_PACKET_DEFAULT to
100*CHAN_SES_PACKET_DEFAULT.
Below is an excerpt from an updated channels.h, with
the change indicated in red:
#define CHAN_EXTENDED_IGNORE 0
#define CHAN_EXTENDED_READ 1
#define CHAN_EXTENDED_WRITE 2
/* default window/packet sizes for tcp/x11-fwd-channel */
#define CHAN_SES_PACKET_DEFAULT (32*1024)
#define CHAN_SES_WINDOW_DEFAULT
(100*CHAN_SES_PACKET_DEFAULT) /*?
ORBITAL: changed from 4 to 100 */
#define CHAN_TCP_PACKET_DEFAULT (32*1024)
#define CHAN_TCP_WINDOW_DEFAULT (4*CHAN_TCP_PACKET_DEFAULT)
#define CHAN_X11_PACKET_DEFAULT (16*1024)
#define CHAN_X11_WINDOW_DEFAULT (4*CHAN_X11_PACKET_DEFAULT)

However, I cannot find a similar place inside of
libssh2's codebase to make a change that will work
along these lines. I have tried changing

LIBSSH2_CHANNEL_WINDOW_DEFAULT
LIBSSH2_CHANNEL_PACKET_DEFAULT

with no success.

Change History

comment:1 Changed 10 years ago by bagder

Slow transfers aren't really a bug in libssh2 but unfortunately still mostly a design-issue.

I don't see how any references to openssh helps us, nor do I believe it has to do with the TCP window size. I would not be surprised however if the SSH window size is involved.

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