ETSI TS 101 346 Digital cellular telecommunications system (Phase 2+) (GSM); General Packet Radio Service (GPRS); Serving GPRS Support Node (SGSN) - Visitors Location Register (VLR); Gs interface layer 3 specification (GSM 09.18 version 7.2.0 Release 1998)

standard by European Telecommunications Standards Institute, 11/01/1999