2202 – is a small capacity indoor RBS with maximum configuration 2+2+2. In case of adittional cabinet in can be extended up to 4+4+4.
2206 – large capacity RBS with maximum 4+4+4 configration in standart cabinet.
As I know -2202 is quite old version of RBS2000 series. 2206- is newer one.
Differents of all CDU types is maximum output power per TRU.
Difference between TRU and dTRU, is that dTRU -is duplex TRU. Actually it is 2xTRX in one TRU.