asterisk users - Nov 2014 - Incoming calls to a GSM gateway & "SIP/2.0 401 Unauthorized" response when dial 7777 to Asterisk

Hello:

I'm newbie in asterisk, please help me.

My context is as follows:

192.168.4.2 --> Asterisk 11.13.1 complied from source

192.168.4.4 --> Yeastar NeoGate TG100 GSM gateway

When I call from a GSM cell phone, my TG100 GSM gateway answers and
dials extension 7777 (configured as a hotline on TG100) to asterisk
server, but asterisk server sends me "SIP/2.0 401 Unauthorized"
response, I think it's a matter of contexts but I don't find the
problem.

Attached are sip.conf, extensions.conf and debug from 192.168.4.4
(TG100 GSM gateway).

Thanks in advance.
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