CSFB流程

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MO CSFB

↑ Extended Service Request (in RRC Connnet Setup Complete or information Transfer)

↓RRC Connection Release

↑Channel Request (MS-GSM)

↓Immediate Assignment  (  Message in AGCH，BSC-MS:分配SDCCH )

↑ CM Service Request（MS-MSC）

↑Classmark Change (MS-BSC)

↑GPRS Suspension Request （MS-MSC）

↓CM Service Accept (MSC-MS)

↑Setup (MS-MSC called party number)

↓ Identity Request( MSC-MS,IMEISV )

↑Identity Response (MS-MSC,IMEISV of MS)

↓Call Proceeding(MSC-MS)

↓Assignment Command (Message in SDCCH，BSC-MS,分配TCH)

↑Assignment Complete (Message in TCH)

↓Alerting(Message in TCH ,MSC-MS) 被叫振铃，

↓Connect（Message In TCH，MSC-MS） 被叫接听

↑Connect Acknowledge（MS-MSC）接听确认