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LTE基于X2切换和基于S1切换有什么区别

1:源eNodeB决定进行基于S1的切换。S1切换的原因可能是源eNodeB和目标eNodeB之间不存在X2连接,或者源eNodeB根据其他情况作出的判断。
2:源eNodeB向源MME发送Handover Required消息,主要包括如下一些内容:
IE/Group Name
Presence
Message Type
M
MME UE S1AP ID
M
eNB UE S1AP ID
M
Handover Type
M
Cause
M
Target ID
M
Direct Forwarding Path Availability
O
SRVCC HO Indication
O
Source to Target Transparent Container
M

其中Handover Type在此时是intra-LTE,TargetID包含Target Cell ID和Target TAI两部分(目标TAI信息是从哪里获得的?),源MME可以根据目标 TAI来选定合适的目标MME。 Direct Forwarding Path Avaliability用来指示在源和eNodeB之间是否存在存在直接转发的路径还是需要进行Indirect Tunnel Forwarding。源eNodeB还指明需要进行转发的EPS 承载,在哪里指明?
3:源MME选定合适的目标MME,通过S10接口发送Forward Relocation Request消息给目标MME,包含如下一些主要内容:
IMSI
C
The IMSI shall be included in the message except for the case:
- If the UE is emergency attached and the UE is UICCless.
The IMSI shall be included in the message but not used as an identifier
- if UE is emergency attached but IMSI is not authenticated.

Sender's F-TEID for Control Plane
M
This IE specifies the address and the TEID for control plane message which is chosen by the source MME/SGSN.
This information shall be used by the target MME/SGSN to the source MME/SGSN when sending Forward Relocation Response message, Forward Access Context Acknowledge message and Forward Relocation Complete Notification message.
MME/SGSN UE EPS PDN Connections
M
Several IEs with this type and instance values shall be included as necessary to represent a list of PDN Connections
SGW S11/S4 IP Address and TEID for Control Plane
M
主要应用于SGW不需要Relocation的情形?
SGW node name
C
This IE shall be included if the source MME or SGSN has the source SGW FQDN.
MME/SGSN UE MM Context
M



4:目标MME选定相应的目标SGW,发送Create Session Request消息给目标SGW,消息中包含每个承载的上下文 (针对基于GTP的S5/S8而言,包括PGW的地址和上行GTP-U在PGW侧的TEID值)。目标SGW为数据承载分配上行GTP-U的地址和TEID值,返回Create Session Response消息给源MME。没有分配转发数据的TEID吗?
5:目标MME发送Handover Request消息给目标eNodeB,其中包括要建立的EPS承载的列表等内容,每个EPS承载的信息包括SGW的地址,上行GTP-U的在SGW侧的 TEID值,EPS 承载的QoS等。目标eNodeB收到上述消息后会建立UE上下文,包括承载的信息,安全上下文等。目标eNodeB 也回送Handover Request Ack消息给目标MME,其中包含EPS承载建立结果的信息。对于每个成功建立的EPS承载,其信息包括下行数据在目标eNodeB侧的G

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