On 2018-07-18 23:36, Mark Pizzolato wrote:
On Wednesday, July 18, 2018 at 2:32 PM, Paul Koning wrote:
It might be better to hard set the Linux simh host system's port to
10Mbit on the switch. That would help with the potential for
overrunning the original DEC hardware...
DEC hardware tends to handle line rate traffic; a lot of other Ethernet
hardware does not, especially not earlier models. I remember arguing with the
DECnet/DOS folks that no, we would not modify the DECnet architecture to
handle the single buffer "design" of the 3c501.
But if you have speed mismatches, you're likely to have congestion loss, unless
the bursts are less than the switch buffer quota. Some switches have
thousands of buffers; other (inexpensive) ones have only a surprisingly small
number and can easily give you congestion loss.
Well, not all systems and hardware can actually handle back to back
packets even at 10Mbits. The XQ THROTTLING is based on the throttling that
Johnny Billquist implemented in his bridge which was needed to allow his
physical systems to be able to communicated with simulated systems without
crazy packet loss...
It's probably worth pointing out that the reason I implemented that was
not because of hardware problems, but because of software problems.
DECnet can degenerate pretty badly when packets are lost. And if you
shove packets fast enough at the interface, the interface will
(obviously) eventually run out of buffers, at which point packets will
be dropped.
This is especially noticeable in DECnet/RSX at least. I think I know how
to improve that software, but I have not had enough time to actually try
fixing it. And it is especially noticeable when doing file transfers
over DECnet.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: b...@softjar.se || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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