using pscp.exe for sftp transfer is very slow compared to filezilla

Question

I have a weird problem. I'm using pscp.exe from within a C# program (with process.start) to upload files to an SFTP server. Now I have set up a new server with the same program, where I upload to the same SFTP server as before, but It runs incredibly slow in the new server.

The weird thing is that when I try uploading the files manually via FileZilla, the upload goes as fast as expected, but not when using the program.

Can anyone explain this? Am I missing something obvious like a windows setting or something?

Answer 1

SSH supports what we call pipelining - sending multiple SSH packets without waiting response to each packet. OpenSSH supports this functionality, while Putty doesn't (at least didn't until recently). That's what you observe. Another reason is choice of algorithms. If AES is negotiated, it's faster than DES and 3DES used by default by older applications.