Cellular Network Infrastructure » Radio Access Network » OsmoBSC

When a BTS is not sending CCCH_LOAD_IND with PCH load IE, the BSC must estimate the PCH capacity.

The default configuration is to start sending CCCH_LOAD_IND from 10% PCH load upwards, which means below 10% no such indications are sent.

paging_give_credit() adds 20 slots every 5s in such situations. That's not a lot, and we should be smarter than that.

The BSC knows the CCCH configuration (SDCCH4 or not? BS_AG_BKS_RES etc.) and can hence make some good guess how many downlink PCH blocks the BTS has.

What is hard to eestimate is the amount of batching into higher-order PCH messages (multiple identities per MAC block) is happening in the BTS, as it's an implementation detail and it depends on the identity types being paged. But we should take a conservative estimate (one paging per block) and then at least assume that as capacity.

That conservative estimate should then certainly get us above the (default 10%) threshold so the flow control can kick in.