【5G学习笔记-7】38.331 NR RRC_INACTIVE态

 

38.331中:

RRCRelease 含义如下:

The RRCRelease message is used to command the release of an RRC connection or the suspension of the RRC connection.

Signalling radio bearer: SRB1

RLC-SAP: AM

Logical channel: DCCH

Direction: Network to UE

suspension of the RRC connection就是指进入到RRC_INACTIVE态。

在状态机的图中 RRC_CONNECTED收到Release with suspend会切到RRC_INACTIVE态。这个Release with suspend就是指包含 suspendConfig字段的的RRCRelase 消息。

suspendConfig Indicates configuration for the RRC_INACTIVE state. The network does not configure suspendConfig when the network redirect the UE to an inter-RAT carrier frequency.

SuspendConfig field descriptions

ran-NotificationAreaInfo Network ensures that the UE in RRC_INACTIVE always has a valid ran-NotificationAreaInfo.

ran-PagingCycle Refers to the UE specific cycle for RAN-initiated paging. Value rf32 corresponds to 32 radio frames, value rf64 corresponds to 64 radio frames and so on.

t380 Refers to the timer that triggers the periodic RNAU procedure in UE. Value min5 corresponds to 5 minutes, value min10 corresponds to 10 minutes and so on.

在38.331 的5.3.8.3            Reception of the RRCRelease by the UE节中描述如下:

1>  if the RRCRelease includes suspendConfig:

2>  apply the received suspendConfig;

2>  reset MAC and release the default MAC Cell Group configuration, if any;

2>  re-establish RLC entities for SRB1;

2>  if the RRCRelease message with suspendConfig was received in response to an RRCResumeRequest or an RRCResumeRequest1:

3>  stop the timer T319 if running;

3>  in the stored UE Inactive AS context:

4>  replace the KgNB and KRRCint keys with the current KgNB and KRRCint keys;

4>  replace the C-RNTI with the temporary C-RNTI in the cell the UE has received the RRCRelease message;

4>  replace the cellIdentity with the cellIdentity of the cell the UE has received the RRCRelease message;

4>  replace the physical cell identitywith the physical cell identity of the cell the UE has received the RRCRelease message;

2>  else:

3>  store in the UE Inactive AS Contextthe current KgNB and KRRCint keys,the ROHC state, the C-RNTI used in the source PCell, the cellIdentity and the physical cell identity of the source PCell, and all other parameters configured except for the ones withinReconfigurationWithSync and servingCellConfigCommonSIB;

2>  suspend all SRB(s) and DRB(s), except SRB0;

2>  indicate PDCP suspend to lower layers of all DRBs;

2>  if the t380 is included:

3>  start timer T380, with the timer value set to t380;

2>  if the RRCRelease message is including the waitTime:

3>  start timer T302 with the value set to the waitTime;

3>  inform upper layers that access barring is applicable for all access categories except categories '0' and '2';

2>  if T390 is running:

3>  stop timer T390 for all access categories;

3>  perform the actions as specified in 5.3.14.4;

2>  indicate the suspension of the RRC connection to upper layers;

2>  enter RRC_INACTIVE and perform cell selection as specified in TS 38.304 [20];

 

终端进入 RRC_INACTIVE 后，按照 TS 38.304User Equipment (UE) procedures in Idlemode and RRC Inactive state协议要求运行。

 

38.331 B.1      Protection of RRC messages 

RRCRelease 的完整性和安全要求:

Justification for P: If the RRC connection only for signalling not requiring DRBs or ciphered messages, or the signalling connection has to be released prematurely, this message is sent as unprotected.  RRCRelease message sent before AS security activation cannot include deprioritisationReq, suspendConfig, redirectedCarrierInfo, cellReselectionPriorities information fields.

 

另外一直以为只有5G RRC才有RRC INACTIVE态，但是从协议38.331的下图看来，LTE RRC也是有三个状态的。38.331的早期版本中，这个图里LTE还是只有两个状态的。LTE的RRC INACTIVE和5G NR有何差异，LTE何时引入的这个状态，需要后面再学习学习。