Mpd provides summary traffic statistics in every accounting Update/Stop call of radius-acct or ext-acct.
For radius-acct it provides such attributes:
Acct-Input-Packets32bit input packets counter,
Acct-Output-Packets32bit output packets counter,
Acct-Input-Octetslower 32bit of input bytes counter,
Acct-Output-Octetslower 32bit of output bytes counter,
Acct-Input-Gigawordshigher 32bit of input bytes counter,
Acct-Output-Gigawordshigher 32bit of output bytes counter.
For ext-acct it provides:
ACCT_INPUT_PACKETS64bit input packets counter,
ACCT_OUTPUT_PACKETS64bit output packets counter,
ACCT_INPUT_OCTETS64bit input bytes counter,
ACCT_OUTPUT_OCTETS64bit output bytes counter.
NOTE: as Accounting Update is implemented on a link layer it accounts traffic via single physical link (without link overhead). So it accounts traffic after compression, encryption and multilink were applied to it.