The purpose of the Gb proxy is to aggregate the Gb links of multiple BSS's and present them in one Gb link to the SGSN.

The SGSN implements - the Gb interface to the BSS's (like the OsmoPCU or an ip.access nanoBTS) - the Gp interface with its GTP protocol to one or more Gateway GPRS Support Node (GGSN) like OsmoGGSN. - the IuPS interface with its RANAP protocol to onre or more RNCs or HNB-GWs like OsmoHNBGW - the GSUP Interface/Protocol towards OsmoHLR