本文讲述终端TAU需要进行能力更新的场景。

终端attach成功后TAU

终端在attach到2/3/4/5G成功后，进行路由更新时需要携带终端的能力信息。

参考3GPP TS 23.401 5.5.3.2.2，

if the UE initiates the first tracking area updating procedure following an attach in A/Gb mode or Iu mode,

the UE shall include a UE radio capability information update needed IE in the TRACKING AREA UPDATE REQUEST message.

If the UE initiates the first tracking area updating procedure following an initial registration in N1 mode and the UE is operating in the single-registration mode,

the UE shall include a UE radio capability information update needed IE in the TRACKING AREA UPDATE REQUEST message.

终端能力改变后TAU

终端从NSA制式切到LTE或者NG SA，进行路由更新时需要携带能力信息。

参考3GPP TS 23.401, 5.5.3.2.2, Case n), za), zc)

For cases n, za and zc, the UE shall include a UE radio capability information update needed IE in the TRACKING AREA UPDATE REQUEST message.

If the UE is in the EMM-CONNECTED mode and the UE changes the radio capability for E-UTRAN or for NG-RAN, the UE may locally release the established NAS signalling connection and enter the EMM-IDLE mode.

Then, the UE shall initiate the tracking area updating procedure including a UE radio capability information update needed IE in the TRACKING AREA UPDATE REQUEST message.

终端AS层能力改变

AS层请求能力更新，进行TAU时需要携带能力信息。

hVoLTE模式改变

hVoLTE开启情况下，终端会根据VoLTE注册状态，自动在VoLTE/LTE only和SRLTE模式之间切换，为了保证电话业务正常。

hVoLTE模式改变后，TAU需要携带能力信息。