PPP troubling with large messages > 1.4kB (esp32)
I have a PPP connection with a SIM7000E module and just realized that large messages don't reach the target.
In my case, I want to send "large" messages via MQTT. From a size of around 1.4kB, the messages don't arrive at the MQTT broker anymore. I tested the same messages with WiFi and could send messages of up to 4.4kB. Unfortunately, I do not get any Error that tells me what might go wrong.
To me, this looks like a limit due to some buffer. Is it possible to increase this buffer or is there another alternative to handle large messages?
EDIT: Just realized that in the case of PPP, this is about the Ethernet MTU and therefore no fragmentation taking place?
EDIT: I verified also for uping tool (https://gist.github.com/shawwwn/91cc8979e33e82af6d99ec34c38195fb). I experienced the same size limit here. So this seems to be a general limit in the PPP implementation,
ESP32: persistent PPP needed
Currently PPP tries to connect during some time, around 10 seconds
and then it gives up. After the timeout, PPP's serial traffic which looks
like !}!}!} }4}"}&} } } } }%}&y is no longer active at serial line and other
end (pppd linux) can't establish connection after timeout.
In application I would need PPP to continuously be active
because if I restart PPP by deleting its instance and creating again
after ESP32 has connected to WiFi, then PPP will spoil WiFi routing
and I don't want this to happen.
Additionaly - is this bug? This won't manually restart PPP after timeout:
ppp.active(False)
ppp.active(True)
Does nothing, while I think it should reactivate PPP traffic to
attempt connection on serial line, the chars !}!}!} }4}"}&} } } } }%}&y
should appear again