The Traffic Manager - Traffic Monitor page on my router reports drastically less bandwidth data usage than our ISP. For example 2015-Nov-04 is 0.98GB according to Asus and 7.3GB according to ISP. This has been the case since I bought the router a couple of years ago, but it's not been important enough to get to the bottom of until now.
For awhile I wondered if someone else in the city might be using my cable MAC address a la DerEngel. I think this unlikely, those methods are a dozen plus years old and well publicized. Also our ISP offers usage stats down to 30 minute intervals and the near-zero holes in those mirror occasions when there is no one home or everyone is asleep.
On the other hand Asus is a respected manufacturer known for their technical capabilities.
How do I determine with confidence why the numbers differ?
There is a single ethernet cable from the modem, going to the router. Put another way, all traffic from the house goes through the router before getting to the modem.
The router typically has 3 wired clients and up to 9 wifi clients. (I recognize all of the devices listed in the router DHCP lease table, no parasites here).
The devices run everything from Windows to Linux to iOS to Android to I-don't-know (DS,wii), so client side monitoring apps is unlikely to be practical.
Router: Asus RT-N56U, firmware version:3.0.0.4.376_1665
Modem: Cisco DPC3008 DOCSIS 3.0
Update: sample tables from router and ISP
Update 2: combine tables and show variance (difference between reported totals)
+------------+------+------+----------+---+------+------+----------+---+----------+
| Date | R_Up | R_Dn | R_Total | | I_Up | I_Dn | I_Total | | Variance |
+------------+------+------+----------+---+------+------+----------+---+----------+
| 11/4/2015 | 0.86 | 0.12 | 0.98 GB | | 0.30 | 6.99 | 7.29 GB | | 6.31 GB |
| 11/5/2015 | 1.02 | 0.07 | 1.09 GB | | 0.13 | 4.09 | 4.22 GB | | 3.13 GB |
| 11/6/2015 | 0.83 | 0.10 | 0.93 GB | | 0.23 | 4.01 | 4.24 GB | | 3.31 GB |
| 11/7/2015 | 1.48 | 0.09 | 1.57 GB | | 0.18 | 5.84 | 6.01 GB | | 4.44 GB |
| 11/8/2015 | 0.71 | 0.06 | 0.77 GB | | 0.27 | 3.12 | 3.39 GB | | 2.62 GB |
| 11/9/2015 | 1.45 | 0.09 | 1.54 GB | | 0.35 | 4.08 | 4.42 GB | | 2.88 GB |
| 11/10/2015 | 1.12 | 0.08 | 1.20 GB | | 0.20 | 4.41 | 4.60 GB | | 3.40 GB |
| 11/11/2015 | 2.05 | 0.18 | 2.23 GB | | 0.43 | 6.48 | 6.91 GB | | 4.68 GB |
| 11/12/2015 | 1.14 | 0.09 | 1.23 GB | | 0.35 | 4.56 | 4.92 GB | | 3.69 GB |
| 11/13/2015 | 2.44 | 0.13 | 2.57 GB | | 0.29 | 4.04 | 4.33 GB | | 1.76 GB |
| 11/14/2015 | 2.78 | 0.15 | 2.94 GB | | 0.34 | 6.04 | 6.38 GB | | 3.44 GB |
| 11/15/2015 | 0.62 | 0.11 | 0.73 GB | | 0.12 | 0.85 | 0.97 GB | | 0.24 GB |
+------------+------+------+----------+---+------+------+----------+---+----------+
