The Modem and the Gateway are in constant communication. That communication is going to include ... Command & Control signals as well as data used and remaining being communicated back and forth between the terminal and the Gateway. The reporting is not "real time" so it is possible, even likely that data being used by unseen processes for example will not be reported to the Gateway and then displayed in your usage meter until sometime after the fact.
Power off the modem breaks that communication chain and increases the delay until sync is re-established.
Frankly, you would be better served by leaving the modem powered up and free to keep in sync with the Gateway but limit your exposure by disconnecting the LAN cable from the rear of the modem.
Disregard the address as these graphics were prepared for something else but .....:
The path for full connectivity:
Disconnecting the Ethernet cable between the Router and the Modem gives you this:
All of your devices are isolated from the net on the WAN side of your Network but are free to communicate with all devices locally on your Networks local side.
At the same time it maintains the "Loop" that exists between the Modem and the Gateway that allows Command & Control to remain established:
The above will limit your usage exposure to zero while allowing the most up to date data info being displayed.
We are NOT going to leave the modem powered-up because I have read too much about these "unseen processes." If the modem is powered-down, there will be no "unseen processes" sucking our data. I have obtained an ASUS router as you suggested in another thread (screenshots below), and it confirms there were no "unseen processes."
As I said, we have very good reasons (other than the above) for not leaving all our electronics on at all times. We are off-grid, and choose to conserve energy rather than run a fossil-fuel generator. We were assured by our installer that powering-down would not be a problem *at all*, and that it would just re-synchronize when we powered-up again. If this is not the case, we need to know that NOW. gwalk, you have been very helpful, but I think I need to hear from an Exede employee here...
Gwalk, I like the ASUS router a lot. I got the AC1900, from Newegg. I am just running the stock firmware. I am still finding my way around the user interface. Do you run the asuswrt-merlin firmware, and if so, what are the advantages?