Thank you Pavel and Vanderley for the answers, sorry I didn’t check them out earlier.
Lately, I learnt that the extra Abis timeslots are NOT dedicated to one sector (like in older releases) but to the whole BTS. It’s like a pool of Abis TS. So what you need to know is, as Pavel said, the amount of data traffic expected in one BTS. For instance, at peak hour : 2 mobiles connected in MCS-9 with 4 DL PDCH in the BTS = 2 MS x 4 PDCH x 5 nibbles = 40 nibbles = 10 Abis TS.
Furthermore, the Abis nibbles dedicated to the BCCH and SDCCH can be used as extra Abis timeslots (since they are not used on the abis nibbles : they use the dedicated signalling links Abis timeslot).
With the first example :
3 sectors = 3 BCCH + 6 SDCCH = 9 empty Abis nibbles that can be used for EDGE
2 MS 4+1 = 2 x 4 radio TS = 8 Abis nibbles already reserved for voice
So in the end, you only need :
40 – 9 – 8 nibbles = 23 Abis nibbles, in other words you only need (23/4) = 6 additional Abis TS.
Instead of 12 additional Abis TS with “static abis”. Quite a great benefit ! 🙂
I’d be glad to discuss this more if anyone needs support.