当前位置：首页 > java >正文

LTE重建到新小区流程介绍

java 2025/6/25 23:30:03

1.重建介绍

1.1UE发起重建的条件及目的

[From TS 36331]

The purpose of this procedure is to re-establish the RRC connection, which involves the resumption of SRB1 operation, the re-activation of security and the configuration of only the PCell.

A UE in RRC_CONNECTED, for which security has been activated, may initiate the procedure in order to continue the RRC connection. The connection re-establishment succeeds only if the concerned cell is prepared i.e. has a valid UE context. In case E-UTRAN accepts the re-establishment, SRB1 operation resumes while the operation of other radio bearers remains suspended. If AS security has not been activated, the UE does not initiate the procedure but instead moves to RRC_IDLE directly.

E-UTRAN applies the procedure as follows:

- to reconfigure SRB1 and to resume data transfer only for this RB;

- to re-activate AS security without changing algorithms.

1.UE发起重建的条件及重建成功的前提条件

（1）UE发起重建条件：UE处于RRC_CONNECTED ，且AS 侧安全已激活，可以发起重建流程继续RRC 连接。如果AS侧安全未激活，则UE不能发起RRC重建流程，而是会直接移动到RRC_IDLE状态。

（2）重建成功的前提条件：相关小区准备好UE上下文。

2.重建的目的：

（1）重配SRB1；

（2）重新激活AS侧安全能力，且不改变算法。

1.2 UE发起重建的原因

The UE shall only initiate the procedure when AS security has been activated. The UE initiates the procedure when one of the following conditions is met:

1> upon detecting radio link failure,; or

1> upon handover failure ; or

1> upon mobility from E-UTRA failure; or

1> upon integrity check failure indication from lower layers; or

1> upon an RRC connection reconfiguration failure

2.重建到新小区流程

2.1 UE发起RRCReestablishmentRequest

The UE shall set the contents of RRCConnectionReestablishmentRequest message as follows:

1> set the ue-Identity as follows:

2> set the c-RNTI to the C-RNTI used in the source PCell (handover and mobility from E-UTRA failure) or used in the PCell in which the trigger for the re-establishment occurred (other cases);

2> set the physCellId to the physical cell identity of the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases);

2> set the shortMAC-I to the 16 least significant bits of the MAC-I calculated:

3> over the ASN.1 encoded as per section 8 (i.e., a multiple of 8 bits) VarShortMAC-Input;

3> with the KRRCint key and integrity protection algorithm that was used in the source PCell (handover and mobility from E-UTRA failure) or of the PCell in which the trigger for the re-establishment occurred (other cases); and

3> with all input bits for COUNT, BEARER and DIRECTION set to binary ones;

1> set the reestablishmentCause as follows:

2> if the re-establishment procedure was initiated due to reconfiguration failure as specified in 5.3.5.5 (the UE is unable to comply with the reconfiguration):

3> set the reestablishmentCause to the value 'reconfigurationFailure';

2> else if the re-establishment procedure was initiated due to handover failure as specified in 5.3.5.6 (intra-LTE handover failure) or 5.4.3.5 (inter-RAT mobility from EUTRA failure):

3> set the reestablishmentCause to the value 'handoverFailure';

2> else:

3> set the reestablishmentCause to the value 'otherFailure';

The UE shall submit the RRCConnectionReestablishmentRequest message to lower layers for transmission.

2.2 基站侧处理 RRCReestablishmentRequest

（1）接收并解析RRCReestablishmentRequest，验证UE身份

1>通过PCI确认UE是否重建到原小区。

2>若PCI相同，则UE重建到原小区，通过crnti 查找UE上下文，并检测shortMAC-I是否匹配

2>若PCI不同，通过 X2接口向其他小区请求UE上下文，再通过crnti 查找UE上下文，并检测shortMAC-I是否匹配

（2）shortMAC-I计算需要以下输入参数VarShortMAC-Input

TS36331-7.1

TS33401 -7.4.3

2.3 X2接口向其他小区请求UE上下文

[From 36423]

2.3.1 RETRIEVE UE CONTEXT REQUEST

重建目标小区发起RETRIEVE UE CONTEXT REQUEST

The new eNB initiates the procedure by sending the RETRIEVE UE CONTEXT REQUEST message to the old eNB.

If the old eNB is able to identify the UE context and to successfully verify the UE by means of the Resume ID, the ShortMAC-I, optionally the C-RNTI, the failure cell PCI and the E-UTRAN Cell Identifier of the new cell contained in the RETRIEVE UE CONTEXT REQUEST message, it shall respond with the RETRIEVE UE CONTEXT RESPONSE message. The allocation of resources according to the values of the Allocation and Retention Priority IE included in the E-RAB Level QoS Parameters IE shall follow the principles described for the E-RAB Setup procedure in TS 36.413 [4].

If the C-RNTI IE is present in the RETRIEVE UE CONTEXT REQUEST, the old eNB shall ignore the Resume ID IE.