LTE 中设置voice/data centric的差异

1.  什么是voice centric和data centric

        Voice centric和data centric的差别在于以语音为中心还是以数据为中心。这里的以某某为中心可不是说说而已。举个栗子，UE一般搜网注册都会按照LUG（LTE->UMTS->GSM）或者LC（LTE->CDMA）的顺序进行，如果UE（未开通VOLTE）注册到LTE时，网络提示不支持语音，比如CSFB。UE就必须disable LTE后回到GU或者CDMA，否则留在不能语音的网络下，UE就会出现打不出去，呼不进来的窘境。一般支持多模的语音设备，都会默认开启voice centric。
        如果该UE不支持语音，则要求设置为data centric。比如常用的E5、CPE多数产品。数据业务功能是第一优先级的，不可能因为LTE下不支持语音的情况发生时离开LTE，到一个网络速度低的接入技术下。
        从协议的角度，我们看看这两种设置的差别。
        UE's usage setting: This is a UE setting that indicates whether the UE has preference for voice services over data services or vice-versa. If a UE has preference for voice services, then the UE's usage setting is "voice centric". If a UE has preference for data services, then the UE's usage setting is "data centric". A UE whose setting is "data centric" may still require access to voice services. A UE whose setting is "voice centric" may still require access to data services. This definition is derived from 3GPP TS 23.221 [8A] and it applies to voice capable UEs.

       设置data centric可以请求语音服务，设置为voice centric也可以请求数据服务。并不会因为设置了voice centric导致数据能力被限制，这个地方只是优先级的差异。比如，设置为data centric的UE（支持语音）来到支持语音的LTE网络下，它也是可以正常进行语音能力的。
a)  The UE is operating in PS mode 1 or PS mode 2

Table 4.3.2.2.1: Change of UE's usage setting for a UE in PS mode 1 or PS mode 2

UE's usage setting change
Procedure to execute
From data centric to voice centric and "IMS voice not available"
Disable the E-UTRA capability if voice domain selection results in a selection to a different RAT (see subclause 4.5), or combined tracking area update with IMSI attach if voice domain selection results in attempt to stay in E-UTRAN.
 
From voice centric to data centric and E-UTRA is disabled
Re-enable the E-UTRA capability (see subclause 4.5)
 

b)  The UE is operating in CS/PS mode 1 or CS/PS mode 2

Table 4.3.2.2.2: Change of UE's usage setting for a UE in CS/PS mode 1 or CS/PS mode 2

UE's usage setting change
Procedure to execute
From data centric to voice centric, "CS fallback is not available" and "IMS voice not available" (NOTE 1)
Disable the E-UTRA capability (see subclause 4.5)
 
From data centric to voice centric, "IMS voice not available" and the UE received a "CS fallback not preferred" or "SMS only" indication during the last successful combined attach or combined tracking area updating procedure
Disable the E-UTRA capability (see subclause 4.5)
 
From voice centric to data centric and E-UTRA is disabled
Re-enable the E-UTRA capability (see subclause 4.5)
NOTE 1:   "CS fallback is not available" includes EMM causes #16, #17, and #18
 
        对于PS mode1，voice centric。如果注册提示IMS voice not available。则要求UE disable LTE或者联合TAU/IMSI注册。
        对于PS mode2，data centric。则不受上面情况影响，直接使能LTE。
        对于CS/PS mode1，voice centric。如果注册提示CS fallback is not available并且IMS voice not available。则会disable LTE。另外一种情况是，IMS voice not available并且CS fallback not preferred或者SMS only，也会disable LTE。
        对于CS/PS mode2，data centric。则不受上面情况影响，直接使能LTE。
 
2. 产品该配置voice centric还是data centric  

        对支持VOLTE的电信产品，无论ATTACH请求中是Combined还是EPS ONLY类型。目前现网下网络都会以EPS ONLY处理。
        导致的结果是如果LTE注册成功，但是VOLTE注册失败。产品将失去通话能力。为此，手机的解决方案是SRLTE。即产品发现VOLTE注册失败后，会注册1X。使得数据业务在LTE下，而语音在1X上。
        对于只支持电信LTE的支持语音的单模产品，因为没有1X。如果VOLTE注册失败，也不能回到1X，所以建议设置为data centric。当然设置为voice centric，因为回不到1x，只能留在LTE，和data centric其实一样。
        单模产品除外，其他情况支持语音的话，均建议设置为voice centric。