1. 3GPP. TS 23.002 : Universal Mobile Telecommunications System (UMTS) ; Network architecture (Release 5), Sept. 2003 . https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=728. 3GPP. TS 23.002: Universal Mobile Telecommunications System (UMTS); Network architecture (Release 5), Sept. 2003. https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=728.
2. 3GPP. TS 29.211 : Rx Interface and Rx/Gx signalling flows (Release 6) , June 2007 . https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1671. 3GPP. TS 29.211: Rx Interface and Rx/Gx signalling flows (Release 6), June 2007. https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1671.
3. 3GPP. TS 23.167 : IP Multimedia Subsystem (IMS) emergency sessions (Release 17) , Sept. 2021 . https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=799. 3GPP. TS 23.167: IP Multimedia Subsystem (IMS) emergency sessions (Release 17), Sept. 2021. https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=799.
4. 3GPP. TS 23.228 : IP Multimedia Subsystem (IMS) ; Stage 2 (Release 17), Dec. 2021 . https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=821. 3GPP. TS 23.228: IP Multimedia Subsystem (IMS); Stage 2 (Release 17), Dec. 2021. https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=821.
5. 3GPP. TS 23.501 : System architecture for the 5G System (5GS) (Release 17) , Dec. 2021 . https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=3144. 3GPP. TS 23.501: System architecture for the 5G System (5GS) (Release 17), Dec. 2021. https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=3144.