[Asterisk-Users] double-dial in SIP Grandstream

[Marc SCHAEFER]

Hi,

I have even now connected to IAXtel at number 1-700-895-5211
when I am in the office, so Asterisk is great.

I just found something strange, which is that if I am already in a
connection with my Grandstream and talking, and a second call comes in,
it rings on the Grandstream.

However, if I am not talking but waiting for dialing, the caller gets a
busy signal (good).

How can I make sure there is only one call at a time to the SIP phone ?
(call waiting could be useful, but I didn't figure out how to do this
with the SIP).