Working with AT&T support, I am been told the MC8705 has sent incorrect CHAP information if modem activates PDP context via ATD99**1 command, and PPP mode.
=== ================================
CHAP failure due to Value and hostname

Activate PDP context with ATDT 99**1#

Octet114 CHAP Challenge

00000001 Code (1) Challenge
00000001 Identifier 1
… Length 35
00010000 Value Size 16
… Value 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
… Name UMTS_CHAP_SRVR

Octet149 Protocol ID

… Protocol ID (49699) CHAP Challenge Handshake Authentication Protocol
00101000 Parameter length 40

Octet152 CHAP Response

00000010 Code (2) Response
00000001 Identifier 1
… Length 40
00010000 Value Size 16
… Value 7E CE 08 54 22 0C 9A 8F 8F C1 DB 07 66 33 C2 2F
… Name usertest

If I activate via AT+CGACT=1,1 then CHAP authentication is OK. The difference of those 2 activation methods are CHAP server name and Value in CHAP challenge, which is sent from MC8705.

And here is the trace of success authentication

=== ==============================
CHAP authen OK
Activate PDP context with AT+CGACT=1

Octet114 CHAP Challenge

00000001 Code (1) Challenge
00000000 Identifier 0
… Length 33
00010000 Value Size 16
… Value 0B AB 8B 8B 0B AB 8B 8B 0B AB 8B 8B 0B AB 8B 8B
… Name umts-net.net

Octet147 Protocol ID

… Protocol ID (49699) CHAP Challenge Handshake Authentication Protocol
00101000 Parameter length 40

Octet150 CHAP Response

00000010 Code (2) Response
00000000 Identifier 0
… Length 40
00010000 Value Size 16
… Value 1C 1A 88 CA 45 B6 79 7A 89 02 CA 77 35 79 35 A1

Look like this is a bug in MC8705 firmware. I have contacted to Sierra but it takes so long . Any comment is greatly appreciated.

May I know anyone has encountered the same problem as mine when connect to Wireless network with authentication ON.

Thanks.