USSD流程

请问各位 USSD的信令流程是怎么样的，我这里有一段MS端的信令流程不知道 如何分析

[MS->NW] MM__CM_SERVICE_REQUEST

[NW->MS] RR__IMMEDIATE_ASSIGNMENT

[MS->NW] RR__CLASSMARK_CHANGE

[MS->NW] RR__GPRS_SUSPEND_REQUEST

[NW->MS] RR__CIPHER_MODE_COMMAND

[MS->NW] RR__CIPHER_MODE_COMPLETE

[MS->NW] CISS__REGISTER

[MS->NW] RR__MEASUREMENT_REPORT

[MS->NW] RR__MEASUREMENT_REPORT

[MS->NW] RR__MEASUREMENT_REPORT

[NW->MS] CISS__RELEASE_COMPLETE

[NW->MS] RR__CHANNEL_RELEASE

[MS->NW] RR__MEASUREMENT_REPORT