Home Network Speed (ftp vs scp)

I get about twice the throughput on my 10/100 network with ftp than with scp
(8.6 MB/s vs 4.6) transferring the same file.

Can this be explained by the compression or encryption that scp does? I
can't picture how it would make a difference, since bytes are bytes. I can
understand the CPU having to work harder to decompress or decrypt, but not
the pipe.

ftp
674015232 bytes received in 01:14 (8.63 MB/s)

scp
nx1 18% 117MB 4.6MB/s 01:53 ETA

Buck Turgidson <jc_va@hotmail.com> wrote in message news:<TVDHb.18941$Fg.12239@lakeread01>...
> I get about twice the throughput on my 10/100 network with ftp than with scp
> (8.6 MB/s vs 4.6) transferring the same file.
>
> Can this be explained by the compression or encryption that scp does? I
> can't picture how it would make a difference, since bytes are bytes. I can
> understand the CPU having to work harder to decompress or decrypt, but not
> the pipe.
>
> ftp
> 674015232 bytes received in 01:14 (8.63 MB/s)
>
> scp
> nx1 18% 117MB 4.6MB/s 01:53 ETA

FTP transfers the bytes "as is", ie., the bytes read from disk are
sent down the wire without changes. Once received, job done.

SSH reads bytes from disk, encrypts them, _then_ sends them down the
wire. Once received, the bytes read from the wire must be decrypted
and returned to their original state before writing them to disk. Now
the job is done.

The bytes sent by FTP are _not_ the same bytes sent by SSH's scp.
Bytes are not just bytes, just as mosquito bytes are not the same as
cobra bytes! Otherwise, what's the point of using encryption or
compression?

hth,
prg
email above disabled

P Gentry <rdgentry1@cablelynx.com> wrote:
> Buck Turgidson <jc_va@hotmail.com> wrote in message news:<TVDHb.18941$Fg.12239@lakeread01>...
>> I get about twice the throughput on my 10/100 network with ftp than with scp
>> (8.6 MB/s vs 4.6) transferring the same file.

[snip]

> SSH reads bytes from disk, encrypts them, _then_ sends them down the
> wire. Once received, the bytes read from the wire must be decrypted
> and returned to their original state before writing them to disk. Now
> the job is done.

In addition, it seems from my observations of tcpdump that SSH requires more
packets to send the encrypted info as opposed to plain text. Correct me if I'm
wrong, but my guess is that SSH will use at least double the packets, which
might account for your halved transfer rate.

Any experts who can clarify whether this is the case?

David