关于S1-MME接口中的eNB UE S1AP ID和MME UE S1AP ID

amr

levidoudou 发表于 2014-1-9 13:30
我疑惑的并不是为什么要有两个ID，而是为什么几乎每条消息都同时带有两个ID？按理每次上行消息只需要带MM ...

eNB UE S1AP ID:
        An eNB UE S1AP ID shall be allocated so as to uniquely identify the UE over the S1 interface within an eNB. When an MME receives an eNB UE S1AP ID it shall store it for the duration of the UE-associated logical S1-connection for this UE. Once known to an MME this IE is included in all UE associated S1-AP signalling.
The eNB UE S1AP ID shall be unique within the eNB logical node.

MME UE S1AP ID:
        A MME UE S1AP ID shall be allocated so as to uniquely identify the UE over the S1 interface within the MME. When an eNB receives MME UE S1AP ID it shall store it for the duration of the UE-associated logical
S1-connection for this UE. Once known to an eNB this IE is included in all UE associated S1-AP signalling.
The MME UE S1AP ID shall be unique within the MME logical node.

因为这对ID会发生变化啊，你从协议定义上去理解它。协议上说了，一旦MME/eNB接收到对端的UE SIAP ID，那么在本次的S1链接中都使用这个ID标识UE。

但UE并不是静止不动的，在发生切换，重回服务区或一些异常情况下，网元都变了，这对ID肯定也要发生相应变化。

再者，你可以大致扫描一下S1-AP消息的IE，除REST这种管理层消息或Paging这样的消息是针对所有UE的，无需携带这对ID外，其它都是一对一的消息。

我觉得设计者肯定要制定消息的固定结构。若像你说的本次S1链接不变时只需第一次交换ID就可，其它消息无需携带ID。那这样太繁琐了，而且UE又经常变动，无疑会增加很多问题。