ETSI TS 101 345 Digital cellular telecommunications system (Phase 2+) (GSM); General Packet Radio Service (GPRS); Serving GPRS Support Node (SGSN) - Visitors Location Register (VLR); Gs interface network service specification (GSM 09.16 version 6.1.0 Release 1997)

standard by European Telecommunications Standards Institute, 04/01/1999