This attribute indicates the current number of transmit cells which
are in use for this AtmIf. This attribute is not applicable, and is not
displayed on CQC-based ATM FPs.
Transmit cell memory is used for storing ATM cells to be
transmitted by connections under this AtmIf. It includes all cells in
connections at the nrt-VBR or UBR service category. It includes
cells in CBR or rt-VBR connections which are doing per-VC
queueing. It does not include cells in CBR or rt-VBR connections
which are allocated from the dedicated buffer for CBR common
queuing or rt-VBR common queuing.