08.023GPPBase Station System - Mobile Services Switching Centre (BSS-MSC) Interface - Interface PrinciplesRelease 1999TS
Common and dedicated control channels will be used for the same call on the radio path. These control channels will be multiplexed onto one or more common signalling channel(s) between the BSS and MSC. This multiplexing function will reside at the BSS.
It should be noted therefore that the data links across the air interface are terminated at the BSS.
All scheduling of messages via the air interface is controlled by the base station, flow control is therefore required from BSS to MSC to prevent overload of the transmission buffers, this is further detailed in Technical Specifications 3GPP TS 08.08 and 3GPP TS 08.06.