Hey,
a while ago, we’ve noticed that the PortMaster 3 (RAS, used in the OCTOI hub in Nuremburg) will exhibit bad performance when used in TCP termination mode.
When using X.75, V.120, etc. to connect to a phone number, which is then (through RADIUS) pointed to a TCP socket, the performance is limited to something like 2kByte/s aka 20kBit/s, instead of the correct 64kBit/s.
Using PPP (for internet access), either directly or through the L2TP tunnel feature works perfectly and you can reach 64kbit/s (or even more with bonding).
Curiously, after fixing the OCTOI link issues, I was now able to establish high-speed modem connections reliably for the first time. Interestingly, here the problem also occurs, but to my surprise the exact behaviour also happens to PPP connections!
Analog modem connections are always limited to ~20kbit/s, when connecting to a TCP target or using PPP.
I also thought we already had a bug report for this somewhere, but I couldn’t find it…
I’ve skimmed the PM3 manual for any options like TCP settings, MTU/MSS, compression, etc. but could not find anything that looked immediately suspicious.
@laforge Any insight into firmware versions for the PM3’s? Were there firmware updates? Are our PM3’s running the latest one?
To the community: Ideas? Where would you take a closer look? Network side? ISDN side?
Did something fundamental change in TCP flow control in the past 30 years? (this is 30 year old equipment talking to Linux 6.0 after all)…