ETSI TS 129 018 Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); General Packet Radio Service (GPRS); Serving GPRS Support Node (SGSN) - Visitors Location Register (VLR); Gs interface layer 3 specification (3GPP TS 29.018 version 3.4.1 Release 1999)

standard by European Telecommunications Standards Institute, 04/01/2001