对于一个支持VoLTE的终端，在一个支持VoLTE的网络下开机，网络是如何知道终端具备VoLTE能力从而给建立QCI=5的承载？反过来终端又是如何知道网络具备VoLTE能力，从而发起sip注册的？

终端在注册的时候 attach reqeust会告诉网络终端是否支持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)

同时网络在attach accept时也会告知终端网络是否支持
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)--网络支持