Modem Accounting - Traffic - DL/US

Greetings all users,

I wanted to ask you what would be the best way to get the data rates that a modem is using like : Download traffic speed and upload traffic speed to the ubr10k cmts with different modems/gateways.

1. Is it a good way to read the ifHCIn/OutOctets counters from the modem. If yes which interface id should i read.
Right now i'm doing it like this:
$dl = trim(shell_exec("snmpget -Oqv -v 2c -On -c public {$modemip} 1.3.6.1.2.1.31.1.1.1.6.1"));
$ul = trim(shell_exec("snmpget -Oqv -v 2c -On -c public {$cip} 1.3.6.1.2.1.31.1.1.1.10.1"));
But i see that some of the traffic are not passing through the .1 interface id.

What would be a solution to read this data directly to the cmts through snmp for every modem.

And what solution do you prefer to graph them with rrd.
-> CF -> Max or Average and how many minutes in between should i save the data.

I would be thankful if anyone can support me on this case to get the acquirate data of the traffic accounting from the modems.

Thank you very much.