This counter tracks the number of RELEASE COMPLETE messages, which confirm that SVC teardown has finished and the port has fully freed the connection's resources that this port has transmitted, per the description. Timer T308 depends on this PDU arriving promptly, so this is the counter to check when svcAtmConfigQ93bActiveConns seems to stay elevated longer than expected -- it tells you whether teardown handshakes are actually completing. For example, if NumReleasePduTx keeps rising while NumReleaseCmpltPduRx lags behind, connection resources on this port are likely not being released promptly, which is consistent with a slow leak in active connection count.