通过Um接口监测仪表观察，可能观察到的GPRS ATTACH信令流先后顺序是（）
- A、ATTCHREQUEST-SECURITYFUNCTION-ATTCHACCEPT-ATTCHCOMPLETE
- B、ATTACHREQUEST-SECURITYFUNCTION-ATTACHCOMPLETE-ATTACHACCEPT
- C、ATTACHREQUEST-ATTACHACCEPT-SECURITYFUNCTION-ATTACHCOMPLETE
- D、SECURITYFUNCTION-ATTACHREQUEST-ATTACHACCEPT-ATTACH
正确答案:A
答案解析:有
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