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83GPP. 3GPP TS 23.228 IP Multimedia Subsystem (IMS); Stage2[S]. 2013.
93GPP. 3GPP TS 23.203 Policy Control and Charging Architecture[S]. 2013.
103GPP. 3GPP TS 23.40I General Packet Radio Service (GPR_S) Enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Access[S]. 2014.