This attribute indicates the current number of transmit frames which
are in use for this FP.
On CQC-based ATM FPs, this number indicates the total transmit
frames which are in use for all ports on this FP.
On ATM IP FPs, this number indicates the number of transmit
frames which are in use in the Passport Queue Controller (PQC)
ASIC. Queuing of frames for transmit only occurs in the PQC.