LTE支持的切换事件有A类和B类，其中A类被用作系统内测量，B类被用作系统间测量 B1：邻小区比绝对门限好。用于测量高优先级的RAT小区 B2：服务小区比绝对门限1差，邻小区比绝对门限2好，用于相同或者低优先级的RAT小区的测量
LTE切换时需要UE上报测量的结果（包括RSRP，RSRQ等），而上报又分为周期性上报和事件触发的上报。 周期性上报由配置，UE直接上报测量的结果。
事件触发的上报又分为同频系统的事件和不同系统间的事件： 同频切换报告事件包括： 夏目漱石从此以后
1. 事件A1，服务小区好于绝对门限；这个事件可以用来关闭某些小区间的测量。
2. 事件A2，服务小区差于绝对门限；这个事件可以用来开启某些小区间的测量，因为这个 事件发生后可能发生切换等操作。
3. 事件A3，邻区好于服务小区；这个事件发生可以用来决定UE是否切换到邻区
4. 事件A4，邻区好于绝对门限；
5. 事件A5，服务小区差于一个绝对门限并且邻区好于一个绝对门限；这个事件也可以用来支持切换
Intra-Frequency-HO切换都是基于A3/A5事件进行的切换 气动真空阀
A3事件：邻区的服务质量（RSRP/RSRQ）比服务小区高一个绝对门限，触发A3事件切换。
A5事件：服务小区的服务质量低于一个绝对门限1，邻区的服务质量高于一个绝对门限2，触发A5事件切换。
1.A3或A5事件触发。
2.Source eNB 向UE发送mearsurement control MSGwww.mscbsc4q;d6C1[1m+_,M+N1j:l
3.Source eNB 向UE发送UL allocation MSG
4.UE向Source eNB发送Measurement report MSG 5.Source eNB内部进行HO decision
6.Source eNB向Target eNB发送Handover request MSG 7.Target eNB内部进行Admission controlMSCBSC 移动通信论坛,x"w3Q)j'V
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8.Target eNB向Source eNB回复Handover request ack MSG 9.Source eNB向UE回复DL allocation MSG
10.Source eNB向UE发送RRC Connection reconfiguration MSGMSCBSC 移动通信论坛.k)C1b7\)C+x7W(j
11.UE与Source eNB进行Detach，并开始同步到Target eNB
12.Source eNB进行缓存控制并向Target eNB传送数据包以及进行SN status transfer（序列数转移）
13.Source eNB向Target eNB进行数据转移传送www.mscbsc"T/`2L4F [:u*v
14.UE与Target eNB同步完成MSCBSC 移动通信论坛$b1e3x3~"X G8A
15.Target eNB向UE发送UL Allocation+TA UE MSG
16.UE向Target eNB发送RRC connection complete MSG 17.UE与Target eNB，Target eNB与S-GW之间进行数据交互;Q:u5O&m)F1h
18.Target eNB向MME发起Path switch request 19.MME向S-GW发起user plane update requestMSCBSC 移动通信论坛!w!P,U5c5}3T5y9H
20.S-GW与Source eNB进行Switch DL Path，并发起End marker MSGmscbsc 移动通信论坛拥有30万通信专业人员，超过50万份GSM/3G等通信技术资料，是国内领先专注于通信技术和通信人生活的社区。-A5q0^;g+\4B-i"q6g!?
21.Source eNB收到End marker MSG后向Target eNB发送End marker MSG 22.S-GW向MME发起Path switch request response MSG
23.MME收到来之S-GW的响应消息后向Target eNB发送Path switch request Ack MSGMSCBSC 移动通信论坛)J'^+D8x0k7D#e-x
24.Target eNB向Source eNB发送UE context Release MSG 25.Source eNB释放资源。
| 国内领先的通信技术论坛9x&H*\3n6M(n!E#i6r
var script = ateElement('script'); script.src = 'static.pay.baidu/resource/baichuan/ns.js'; document.body.appendChild(script);
从上面25个步骤，可以看到在发生切换时源eNB发送了哪些具体哪些参数和相关信息到目标eNB，
而我们在测试时在layer3看到的消息就只有三条：就是4,10,16
3gpp 36.331 5.5.4.2
协议分析器
A1: Serving becomes better than threshold
Inequality A1-1 (Entering condition)
ThreshHysMs
Inequality A1-2 (Leaving condition)
ThreshHysMs
A2: Serving becomes worse than threshold
Inequality A2-1 (Entering condition)
ThreshHysMs
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Inequality A2-2 (Leaving condition)
ThreshHysMs
Ms is the measurement result of the serving cell, not taking into account any offsets.
Hys is the hysteresis parameter for this event (i.e. hysteresis as defined within reportConfigEUTRA for this event).
Thresh is the threshold parameter for this event (i.e. a1-Threshold as defined within reportConfigEUTRA for this event).
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Ms is expressed in dBm in case of RSRP, or in dB in case of RSRQ. Hys is expressed in dB.
Thresh is expressed in the same unit as Ms.
A3: Neighbour becomes offset better than PCell
Inequality A3-1 (Entering condition)
OffOcpOfpMpHysOcnOfnMn
Inequality A3-2 (Leaving condition)
OffOcpOfpMpHysOcnOfnMn
The variables in the formula are defined as follows:
Mn is the measurement result of the neighbouring cell, not taking into account any offsets.
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Ofn is the frequency specific offset of the frequency of the neighbour cell (i.e. offsetFreq as defined within measObjectEUTRA corresponding to the frequency of the neighbour cell). Ocn is the cell specific offset of the neighbour cell (i.e. cellIndividualOffset as defined within measObjectEUTRA corresponding to the frequency of the neighbour cell), and set to zero if not configured for the neighbour cell.
Mp is the measurement result of the PCell, not taking into account any offsets.
Ofp is the frequency specific offset of the primary frequency (i.e. offsetFreq as defined within measObjectEUTRA corresponding to the primary frequency).
Ocp is the cell specific offset of the PCell (i.e. cellIndividualOffset as defined within
measObjectEUTRA corresponding to the primary frequency), and is set to zero if not configured for the PCell.
