E1 capacity

For MCS-9 needs 3 Idle Timeslot per 1 PDCH
Mostly cells have 3 PDCHs (1 PDTCH + 2 Dynamic PDCHs)
Total Idle Timeslot per site needed = 3 cells x 3 PDCHs x 3 Idle Timeslots = 27

How many Abis E1s for supporting 27 Idle Timeslots with Site Configuration S4/4/4?
Site Configuration S4/4/4 need number of Abis Sub-timeslot allocation as below.
OML needs 1 timeslot (64kbps) = 4 sub timeslots (16kbps)
RSL for S4/4/4 = 6 timeslots (64kbps) = 24 sub timeslots (16kbps)
TCH for S4/4/4 = (12 TRXs x 8 TCHs) – (3 BCCHs) – (6 SDCCHs) = 87 sub timeslots (16kbps)
Required 27 Idle Timeslots (16kbps)
Total sub timeslots need for S4/4/4 = 4+24+87+27 = 142 sub timeslots = 2 E1s (1 E1 = 124 sub timeslots)