Regarding implementation of RLC/MAC in open BSC

hi , Im new to Open BSC .In your website it is given that "have the BTS interoperate a SGSN with Gb (NS-over-IP) interface " Does this mean that PCU Stacks(RLC/MAC,BSSGP and NS) are implemented at the BTS. Does Open BSC support PCU stacks. Kindly respond. Regards Satish N