Hi Tom Fox,
Let’s call the “RSL” the logical channel for 1 TRX.
Let’s call the “TCH nibble” the 16kb/s sub-channel on the Abis.
One TRX requires 8 TCH nibbles = 8 * 16 = 2 Abis timeslots. (because 1 Abis TS = 4 nibbles = 64kb/s)
Your question regarding the RSL:
1 TRX can require more or less signalling, depending if there are a lot of SDCCH traffic, or half rate traffic.
In normal conditions, 4 RSL are sharing 1 Abis timeslot (64kb/s). The sharing is not static : it is dynamic. Each RSL could sometimes use the full 64kb/s, if the 3 others are idle… (it’s an example)
If RSL is highly loaded, you could decide to share only 2 RSL on the same TS.
So typical RSL usage is 16kb/s in average. Could be up to 32kb/s in special case.