[Info-vax] Slow FTP transfer Linux -> VMS

[John Wallace]

On Aug 28, 8:14 pm, JF Mezei <jfmezei.spam... at vaxination.ca> wrote:
> > does anyone know why the linux box doesn't speed up, and how to solve it?
>
> The only FTP performance parameter on VMS is the system-wide logical name:
>
> "TCPIP$FTP_WNDSIZ" = "4096"
>
> The doc says 4096 is good. I have no idea what the measure is (probably
> 4k of data ?). Not sure if it can be increased much beyond that. This
> affects VMS on the receiving end.
>
> I know that on the dsl line, the VMS box can't get anywhere near the
> maximum throughput (which the Mac next to it can).

But FTP sits on top of TCP, which has some configurable parameters
(e.g. window size stuff, though it seems both TCPIP Services and
Multinet have parameters to allow FTP to override the default), which
sits on top of IP, which has some configurable parameters (e.g. MTU
stuff), which sits on top of hardware which may have some configurable
parameters (eg high-end NIC+switch support for "jumbo frames" etc).

A sub-optimal configuration in any one of these could cause poor
performance.

Then there's "TCP slow start", where disappointing performance doesn't
even need a misconfiguration, just two differing allegedly-correct but
not-really-compatible implementations.

Not a clue what Richard Whalen's "burst limit" is, is it a widely
understood term?

Not a clue what VMS IP stack the original poster is using either,
might it make a difference?