hi pawa,
They are very related, but based on different mechanisms. Altogether, it is congestion on the Abis/Ater link.
1/ Abis congestion:
the number of GCH that can be established is < Nb_GCH_FOR_TBF_ESTAB
2/ Ater congestion:
the number of GCH that can be established is < Nb_GCH_FOR_TBF_ESTAB
3/ Too many TBF:
The number of GCH available to serve the DL TBF is < Min_Nb_GCH.