13GPP TS 48.008: "Digital cellular telecommunications system (Phase 2+); Mobile Switching Centre - Base Station system (MSC-BSS) interface; Layer 3 specification V8.5.0".
23GPP TS 48.008: "General Packet Radio Service (GPRS); Base Station System (BSS) - Serving GPRS Support Node (SGSN); BSS GPRS protocol (BSSGP) V8.1.0".