oh, i missed this thread… sorry RRK, and thanks TNS to bring it up 🙂
with 4 TRX, you should get:
TCH capacity = 21 erlangs
SDCCH capacity = about 8 erlangs (if 2 ts SDCCH/8)
Therefore, it looks like there is a mixup between the SDCCH congestion and the TCH congestion. Are you sure about your indicator’s formula ?
If formulas are right, then what is your timeslots configuration ? (how many TCH and how many SDCCH ?)
with 9 erlangs, in order to reach 50% congestion, i’d say about 10 or 12 timeslots are working as TCH timeslots.
and with 8 erlangs in SDCCH and only 1.5% cong, it sounds like you have 3 ts SDCCH/8 which are up and running.