對于一個支持VoLTE的終端，在一個支持VoLTE的網(wǎng)絡(luò)下開機(jī)，網(wǎng)絡(luò)是如何知道終端具備VoLTE能力從而給建立QCI=5的承載？反過來終端又是如何知道網(wǎng)絡(luò)具備VoLTE能力，從而發(fā)起sip注冊的？

終端在注冊的時候 attach reqeust會告訴網(wǎng)絡(luò)終端是否支持IMS
voice_domain_pref
      length = 1 (0x1)
      UE_usage_setting = 0 (0x0) (Voice centric)
      voice_domain_pref_for_EUTRAN = 3 (0x3) (IMS PS Voice preferred, CS Voice as secondary)

同時網(wǎng)絡(luò)在attach accept時也會告知終端網(wǎng)絡(luò)是否支持
eps_netwk_feature_support
      length = 1 (0x1)
      ESRPS = 0 (0x0)
      CS_LCS = 0 (0x0) (No info about support of loc service via cs is available)
      EPC_LCS = 0 (0x0) (Location Services via EPC not supported)
      EMC_BS = 1 (0x1) (Emergency bearer services in S1 Mode supported)
      IMSVoPS = 1 (0x1) (IMS Vo PS Session in S1 Mode supported)--網(wǎng)絡(luò)支持