N3101 not implemented in OsmoPCU
N3101 is a counter. It counts up for every time no uplink data is received for an assigned USF.
Every time uplik data for an assigned USF is received, the counter is reset to zero.
If the counter ever reaches N3101_MAX, then the USF is no longer placed on the downlink, T3169 started and runs to expiry. After T3169 expiration, the USF is released and can be used by other TBF/MS.