NMT 450 – does anyone know?

I have question if a node should act as GMSC (GSM) but for NMT (as I know it is called MTXG). What minimum fuctionality it has to have. Is is righ that it has to communicate with MTXH (?something as HLR in GSM) by MUP (REM,RIM messages). Is MUP only one possible protocol for communication between MTXG and MTXH or it depends on technology supplier? When MTXG receives routing info it should route the call to appropriate MTXV or MTXH according received routing info? Is it standardized protocol for routing a call from MTXG to MTXV or MTXH? (I see SS7 TUP in some arrow diagrams-it only the possible way or there can be used different ones e.g. ISUP, R2 etc – does anyone have practical experience what is used there?). Where I can get complete specification of NMT from protocol point of view? Thanks for answers!