09.163GPPGeneral Packet Radio Service (GPRS)Gs interface network service specificationServing GPRS Support Node (SGSN) - Visitors Location Register (VLR)TS
The Gs interface connects the Serving GPRS Support Node (SGSN) to the Visitors Location Register (VLR). This interface is defined in the 64 kbit/s for E1 interface and for 64 kbit/s or 56 kbit/s for T1 interface boundary of an SGSN to a VLR or of a VLR to an SGSN. The configuration of the Gs interface shall not impose any restriction on the number of VLRs or SGSNs to be connected by the Gs interface. The Gs interface definition shall support an early implementation of GPRS when one SGSN may be connected to several VLRs or a more mature implementation when several SGSNs may be connected to one VLR. Therefore the interface shall support the use of an STP.
The level of resilience in the Gs interface is determined by the operator, however it is recommended that the operator considers the use of more than one multiplex system between the SGSN and the VLR. Each multiplex system should be used to carry one signalling link and routing diversity should be provided among the signalling links to increase the resilience of the system.