Hello, I was searching for this information virtually everywhere, but as I couldn't find it - I'm asking here. I was wondering, why setting the Compression Level was removed in SSH2, and if on, is always set to 6. In SSH1 it was possible to set the Compression Level from 1 to 9. I have made some tests with Compression Levels using scp: SSH1, compression 9 (highest available for SSH1), vs. SSH2, compression 6 (the only available for SSH2), and, no wonder, SSH1 *always* won, no matter if it was tar'red /etc (lots of txt files), a long pdf file, or even long avi file. Why not let the user what best suits him? Or maybe there is some way to turn it on in SSH2? Regards, Tomasz Chmielewski
Tomasz Chmielewski wrote: [snip]> I was wondering, why setting the Compression Level was removed in SSH2, > and if on, is always set to 6.Unless I read it wrong, the SSHv2 protocol standard does not provide a way to set the compression level [0]. I don't know why this is, perhaps someone else knows the reasoning behind it? See section 5.2 here: http://www.ietf.org/internet-drafts/draft-ietf-secsh-transport-17.txt Compare with the SSHv1 RFC: http://www.zip.com.au/~dtucker/openssh/ssh-rfc-v1.txt (see the description of the SSH_CMSG_REQUEST_COMPRESSION packet type). [0] Ignoring implementation-specific extensions, eg "zlib-1 at openssh.com" through "zlib-9 at openssh.com" or something. -- Darren Tucker (dtucker at zip.com.au) GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4 37C9 C982 80C7 8FF4 FA69 Good judgement comes with experience. Unfortunately, the experience usually comes from bad judgement.
On Fri, 2003-11-07 at 02:36, Tomasz Chmielewski wrote:> Hello, > > I was searching for this information virtually everywhere, but as I > couldn't find it - I'm asking here. > > I was wondering, why setting the Compression Level was removed in SSH2, > and if on, is always set to 6.IIRC protocol 2 doesn't allow negotiation of compression levels, so we have to choose something. 6 is a good tradeoff between CPU and size.> In SSH1 it was possible to set the Compression Level from 1 to 9. > > I have made some tests with Compression Levels using scp: SSH1, > compression 9 (highest available for SSH1), vs. SSH2, compression 6 (the > only available for SSH2), and, no wonder, SSH1 *always* won, no matter > if it was tar'red /etc (lots of txt files), a long pdf file, or even > long avi file.I'm pretty surprised that compressionlevel made any difference with avi or pdf files, which are usually precompressed. Your speed differences were probably due to the fact that protocol 1 is more lightweight (crc instead of MAC, etc - thus also less secure). -d