Fritzbox_netmonitor: measure units and meaning

I configured the fritzbox_netmonitor integration.
So I can see a new sensor called sensor.fritz_netmonitor like this:

Do you know what measure units are these numbers?
max_byte_rate_up/down are related to latest reboot?
Is it possible to see also the dsl connection speed?

I’m collecting these data to an influxdb.
From time to time it looks there are some spikes where the value is also recorded as negative value which is theoretically impossible.
Did you have same experience? How is it possible? How to fix it?