IE/Group Name Message Type eNB UE S1AP ID E-RAB To Be Switched in Downlink List >E-RABs Switched in Downlink Item IEs >> E-RAB ID >> Transport layer address >> GTP-TEID Source MME UE S1AP ID E-UTRAN CGI TAI UE Security Capabilities M M M M M M M Presence M M M 文档名称 Range IE type and reference 9.2.1.1 9.2.3.4 9.2.1.2 9.2.2.1 9.2.2.2 9.2.3.3 9.2.1.38 9.2.3.16 9.2.1.40 To deliver DL PDUs 文档密级：
Semantics description YES YES YES EACH - - - YES YES YES YES Criticality Assigned Criticality reject reject reject reject reject ignore ignore ignore 1 to
MME发送UPDATE USER PLANE REQUEST给S-GW。
2.2.3.5.15 步骤14—Switch DL Path
S-GW把UE的下行数据路劲改变到目标，eNB？cell？S-GW在释放到source eNB的资源之前，先发几个“end marker“消息。
2.2.3.5.16 步骤15-- Update user plane Resp
S-GW发送UPDATE USER PLANE RESPONSE消息给MME。
2.2.3.5.17 步骤16--PATH SWITCH ACKNOWLEDGE
MME发送PATH SWITCH ACKNOWLEDGE消息给target eNB，通知它UE的路径切换已经完成，如果有不能完成的E-RAB，则放在E-RAB To Be Released List信元中。
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IE/Group Name Presence 文档名称 Range IE type and reference Semantics description 文档密级： Criticality Assigned Criticality YES YES YES YES YES EACH - - - YES reject ignore ignore ignore ignore ignore ignore Message Type MME UE S1AP ID eNB UE S1AP ID UE Aggregate Maximum Bit Rate E-RAB To Be Switched in Uplink List > E-RABs Switched in Uplink Item IEs >> E-RAB ID >> Transport Layer Address >> GTP-TEID E-RAB To Be Released List M M M O O M M M O 1 to
target eNB发送UE CONTEXT RELEASE消息给source eNB，通知它切换已经完成，并且触发它释放资源。
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文档名称 文档密级：
2.2.3.5.19 步骤18—Release UE Context
UE释放与source eNB的资源。
注：在消息元中出现的各个简写的意思： Abbreviation Cond conditionTag (Used in downlink only) Conditionally present An information element for which the need is specified by means of conditions. For each conditionTag, the need is specified in a tabular form following the ASN.1 segment. In case, according to the conditions, a field is not present, the UE takes no action and where applicable shall continue to use the existing value (and/ or the associated functionality) unless explicitly stated otherwise in the description of the field itself. Need OP (Used in downlink only) Optionally present An information element that is optional to signal. For downlink messages, the UE is not required to take any special action on absence of the IE beyond what is specified in the procedural text or the field description table following the ASN.1 segment. The UE behaviour on absence should be captured either in the procedural text or in the field description. Need ON (Used in downlink only) Optionally present, No action An information element that is optional to signal. If the message is received by the UE, and in case the information element is absent, the UE takes no action and where applicable shall continue to use the existing value (and/ or the associated functionality). Need OR (Used in downlink only) Optionally present, Release An information element that is optional to signal. If the message is received by the UE, and in case the information element is absent, the UE shall discontinue/ stop using/ delete any existing value (and/ or the associated functionality). Meaning 2.2.3.6 数据处理
在Intra E-UTRAN的切换中，为了避免数据的丢失，需要遵循以下的原则：
? 切换准备期（步骤0~6）
在source eNB和target eNB之间对每一个E-RAB都建立一条上行数据传输通道和下行数据传输通道。 ? 切换执行期（步骤7~11）
数据能够从source eNB发送到target eNB，并且对于下行数据的传输，source eNB需要在接收到EPC的数据后需要按照次序传送给target eNB。 ? 切换结束期（步骤12~18）
Target eNB发送PATH SWITCH信令给MME通知它UE已经获得访问权，然后MME发送USER PALNE UPDATE REQUEST信令给S-GW，这样U-plane path从source eNB切换到target eNB。
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Source eNB仍然需要传送收到EPC的数据给target eNB。
2.2.3.6.1 RLC-AM
? Source eNB通过发送SN STATUS TRANSFER消息通知target eNB下一个需要分配的
PDCP SN，从而保证不会重复传输和in-sequence传输。 ? UE和target eNB都需要一个窗口来检测重复。
? Target eNB优先传送source eNB发来的PDCP SDU，除了收到UE返回的acknowledge。 ? UE重发自上次确认后的PDCP SDU，除了那些因target eNB返回的acknowledge。 2.2.3.6.2 RLC-UM
? Target eNB重置PDCP SN和HFN。 ? Target eNB不会retransmit PDCP SDU。
? Target eNB需要优先传输source eNB发送的数据。
? UE PDCP entity 不会retransmit任何已经成功传送给source eNB的PDCP SDU给target
eNB，只会传输其它的PDCP SDU。
3 LTE与UMTS,GSM重选，重定向，切换
3.1.1 L到U的重选，重定向
针对重选和重定向首先给出RAU的相关信令流程 RAU流程
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