If network has "Internet------Router------MA5200------UserPC". And UserPC is downloading some traffic from Internet.
1) No user-car is configured on MA5200. Here traffic downloaded by UserPC and traffic which passed the router is almost the same.
2) On MA5200 configured user-car limiting connection of UserPC to small bandwidth (much smaller than external channel to Internet behind MA5200). Here traffic actually downloaded by UserPC is noticeably smaller than traffic which passed on the router. (Actual internet traffic consumption is more than useful traffic payload downloaded by UserPC).
MA5200 billing calculate only traffic downloaded by UserPC (traffic which go from MA5200 to UserPC).
As result we have that actually spent Internet traffic is More than total summ of billing data (.lam files from MA5200). This creates unaccounted spent of internet traffic. Sometimes it can be 20% difference or more (depending on total traffic).
Currently on MA5200 it's impossible to count total traffic spent from internet if using user-car on MA5200. Here solution for accounting total traffic is to calculate traffic between Internet and MA5200. For example on router.
This difference of traffic on paths "Internet------Router------MA5200" and "MA5200------UserPC" when using user-car occurs from following reason:
Channel bandwidth from internet to MA5200 is big and from MA5200 to UserPC small. Big traffic come from internet to MA5200 but all traffic can't be transferred to UserPC in time because of small bandwidth, so some part of traffic is discarded and later re-transferred again. So this part of traffic is transferred through router more than 1 time (re-transferred). And MA5200 only calculate traffic transferred to UserPC (no re-transferred traffic).