Please see the model of Ericsson BSC you have supports Network Mode of Operation 1, because BSC and SGSN would needs to be in “NOM1”. Please note, it is only supported in Network Operation Mode 1(NOM1): The Gs interface is installed between the SGSN and the MSC/VLR. The network
can send a CS paging message for a GPRS-attached MS on the same channel as the GPRS paging channel
• the packet paging channel or the CCCH paging channel,
• or on a GPRS traffic channel, if one is currently assigned.
This means that the MS needs only to monitor one paging channel.