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-Packets
32bit input packets counter,
Acct-Output-Packets
32bit output packets counter,
Acct-Input-Octets
lower 32bit of input bytes counter,
Acct-Output-Octets
lower 32bit of output bytes counter,
Acct-Input-Gigawords
higher 32bit of input bytes counter,
Acct-Output-Gigawords
higher 32bit of output bytes counter.
For ext-acct it provides:
ACCT_INPUT_PACKETS
64bit input packets counter,
ACCT_OUTPUT_PACKETS
64bit output packets counter,
ACCT_INPUT_OCTETS
64bit input bytes counter,
ACCT_OUTPUT_OCTETS
64bit 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.