Ok, so it is a number that gives a certain priority to a TRX. I don’t know for your system, but for instance, in alcatel :
0 : lowest priority
7 : highest priority
Example, in one cell :
TRX1 – TRP=1
TRX2 – TRP=0
TRX3 – TRP=0
TRX4 – TRP=0
There is no traffic in the cell.
1st call is setup – the TCH is allocated in TRX1 (highest priority for TCH allocation)
2nd call is setup – the TCH is allocated in TRX1 (highest priority for TCH allocation)
until the TRX1 is totally filled up with TCH. Then the next call is going to be assigned on TRX2, TRX3 or TRX4, depending on internal TCH allocation strategy (cf. your vendor technical documentation)
In this example, the first calls in the cell are going to be assigned on the BCCH frequency. That’s an interesting solution, because the BCCH frequency is usually cleaner than the other frequencies.
(note : this is subject to discussion in case of DL PC and frequency hopping)