This object indicates the fill level of cells in case of
AAL1 adaptation .
The value of this object will be used if the call agent does
not specify partial fill in the MGCP commands (i.e if
L(local connection option):pf( partial fill) is absent).
ATM cell size is 53 bytes, 5 bytes for header, 48 bytes
for data. If the data are not enough to fill 48 bytes of one
ATM cell, the system can fill in the value of this object to
the padding bytes.