LTE 的Data Centric 和 Voice Centric

当终端在发起attach附着请求，或者TAU更新请求时，会携带ue_usage_setting参数，说明终端是DATA centric（以数据为中心）的，还是voice centric（语音为中心）

voice_domain_pref_incl = 1 (0x1)
    voice_domain_pref
      length = 1 (0x1)
      UE_usage_setting = 1 (0x1) (Data centric)
      voice_domain_pref_for_EUTRAN = 2 (0x2) (CS Voice preferred, IMS PS Voice as secondary)

那么究竟什么是 DATA centric，什么是voice centric那？

3GPP 23.221中如下定义
To allow for appropriate domain selection for originating voice calls, a CSFB and/or IMS/CS-voice capable UE is set to behave as “Voice centric” or “Data centric” in E-UTRAN:

• A UE set to “Voice centric” shall always try to ensure that Voice service is possible. A CSFB and an IMS/CS-voice capable UE set to “Voice centric” unable to obtain voice service in E-UTRAN (e.g. CSFB and IMS voice are not supported or the configured preferences on how to handle voice services prevent usage of any available voice services), shall disable the E-UTRAN capability, which results in re-selecting GERAN or UTRAN. The E-UTRAN capability is re-enabled by the UE under the conditions described in TS 24.301 [34]. A voice centric CSFB capable UE that receives “CSFB Not Preferred” or “SMS-only” indication as a result of combined EPS/IMSI attach or combined TA/LA Update procedures and unable to obtain voice services over IMS shall disable the E-UTRAN capability, which results in re-selecting GERAN or UTRAN.
• A UE set to “Data centric” does not disable the E-UTRAN capability if voice services cannot be obtained. Upon receiving combined EPS/IMSI attach accept or combined TA/LA Update accept with “SMS-only” indication, a data centric UE stays in the current RAT and is not allowed to use CSFB. Upon receiving combined EPS/IMSI attach accept or combined TA/LA Update accept with “CSFB Not Preferred” indication, a data centric UE stays in the current RAT and is allowed to use CSFB.

也就是说，voice centric的终端，必须要支持voice功能，如果注册到的LTE网络不支持CSFB，以及IMS等语音业务，那么终端应该关闭LTE的功能，重选回落3G/2G中来，这样用以保证语音业务使用。如果LTE网络支持CSFB/IMS语音业务，那么可以继续停留在LTE网络上。
Data centric的终端，如果注册到的LTE网络，既不支持CSFB，也不支持IMS等业务业务，那么可以继续停留在LTE网络上。

3gpp 24.008 关于voice domain pre以及use’susage setting的定义如下

9.4.1.11 Voice domain preference and UE’s usage setting
This IE shall be included:

• if the MS supports CS fallback and SMS over SGs, or the MS is configured to support IMS voice, or both; and
• if the MS is E-UTRAN capable.

LTE中的Data Centric和Voice Centric含义

Voice domain preference and UE's usage setting value (octet 3, bit 1 to 3)
 
UE's usage setting (1 bit field)
Bit
3
0 Voice centric
1 Data centric
 
Voice domain preference for E-UTRAN (2 bit field)
Bit
2 1
0 0 CS Voice only
0 1 IMS PS Voice only
1 0 CS voice preferred, IMS PS Voice as secondary
1 1 IMS PS voice preferred, CS Voice as secondary
MS not supporting IMS voice shall indicate "CS Voice only".
MS only supporting IMS voice shall indicate "IMS PS Voice only".

如果LTE网络既支持CSFB，又支持IMS多种语音解决方案，那么通话时，究竟使用哪个那？这个就要看voice domain preference参数了

1 0 CS voice preferred, IMS PS Voice as secondary
1 1 IMS PS voice preferred, CS Voice as secondary

如何确定是支持CSFB以及是否支持IMS那，可以通过ATTACH ACCEPT消息，或者TAU ACCEPT消息查看

eps_netwk_feature_support
      length = 1 (0x1)
      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 = 0 (0x0) (Emergency bearer services in S1 Mode not supported)
      IMSVoPS = 0 (0x0) (IMS Vo PS Session in S1 Mode not supported)
    add_update_result_incl = 0 (0x0)
    t3412_ext_incl = 0 (0x0)

add_update_result_incl在3GPP中的定义如下
LTE 中的DataCentric和VoiceCentric含义