[Asterisk-Users] SIP device not able to register but still able to make call

[Sudhir Kumar]

I have a Grandstream HandyTone-486 that is able to make calls through
the asterisk server, but is not able to register. The ATA is behind a
firewall. Could this be because the ISP is blocking something? 

I will appreciate if someone gave me a reasonable explanation of why
this is happening and what could I do to get this fixed.

Thanks,
-- sudhir