【请教】LTE如何区分某个service request是paging response还是mo-data/mo-signaling

admin

找到答案了！在TS24.301的附录D.1。主要原因是为了尽最大可能减少延迟还有就是减少空口的负担（省一个字节都能节省不少资源，LTE就这么抠），service request已经和RRC的连接建立消息合并在一起发送了，所以service request里的service type被取消了，因为RRC的连接建立也需要携带一个原因值来说明建立原因，这service type重复了。

附录D.1截取如下：

Service Request

If a SERVICE REQUEST is to request user plane radio resources, the RRC establishment cause shall be set to MO data. (See Note1)"originating calls"

If a SERVICE REQUEST is to request resources for UL signalling, the RRC establishment cause shall be set to MO data. (See Note 1)"originating calls"

If a SERVICE REQUEST is a response to paging where the CN domain indicator is set to "PS", the RRC establishment cause shall be set to MT access. (See Note 1)"terminating calls"。