Dear, Mouf! As I know there is no signalling relationship between BSC and MGW. All signalling is t*rminated in MSC-server and handled by him. As I know the Ericsson MGW is coupled with Signalling Gateway (SG). SG function is transport conversion from SS7 (MTP) to Sigtran. But an Application Part signalling (BSSAP) is delivered without conversion from BSC to MSC-server. The effect of signalling connection with two MGW is the reserve way for signalling or signalling load sharing.