v2.1 2018-09-14
1. Modified parameter of AT+QLWULDATAEX
(added RELEASE_AFTER_REPLY RAI flag).
2. Added note: network attachment should be triggered
by AT+CGATT=1 but not AT+CFUN=1 in Chapter
3.17.
3. Modified the range of for AT+NSOCR.
v2.0 2018-05-14
1. Added following new AT commands:
AT+CGAUTH/AT+NPIN/AT+NCSEARFCN
2. Updated description of parameters for AT+NPSMR/
AT+QSECSWT/AT+QSETPSK/AT+QLWULDATAEX
3. Added maximum response time for all AT commands
4. Added example for AT+NPING
5. Updated description of error responses
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