I connected a PPPoE through ADSL modem, over a Ethernet port. ADSL modem is connected to the ISP telephone line.

The PPPoE bandwith is limit to 4Mbps by ISP.
Connection between the Ethernet port and the ADSL modem is 100Mbps, which is showed on the interface status page.

Here is a weird graph, on pppoe-interface,
You can see the traffic burst to almost 100Mbps, far beyond the ADSL modem's capability and the telephone line's physical capability. But the Ethernet interface graph is normal. No burst peak. And, I don't known why the pppoe graph data is lost, when I reboot the router around 4am.

How did this happened?

And once at another time, the pppoe is not responding, but I can still see some traffic both Tx and Rx, around 50kbps.
I can't ping any IP successfully including pppoe local-adddress. So I disabled and re-enabled the pppoe, it get back to normal.
Later I found a 70Mbps burst in the graph just when the pppoe get no response. Are they related?