a base station system and method for call setting up , handing over and releasing in hybrid network are disclosed . the base station system consists of bsc , tc , several btss and a band - width guaranteed ip network among them , ip mode transport and traditional tdm mode transport between bsc and tc are simultaneity supported in the system , and bts supports tdm mode or ip mode . the invention is provided with such advantages : compatibility with tdm , which maximumly protects the providers &# 39 ; investment ; smooth transition from tdm to ip , which decreases investing risk ; flexible choice for different physical layer or data link layer transmission apparatuses to bear ip message , which facilitates the providers to constitute their networks . in ip mode , data service can share bandwidth with the mute frames of voice service , the system can coexist with different ip networks such as 3g or wimax , and the control plane and the user plane is independent each other so as to simplify the developing procedure and reduce the maintaining cost .