Busy state. but I didn't refuse

hello. I use asterisk 11 , and realtime cdr. And almost calls operate well.

but sometimes some phone can’t call. ( I call it phone A)

and when I call at the phone(phone A) astersik -rvvv says busy message [SIP/phone A is busy]
even I didn’t refuse.

I think asterisk think the phone A didn’t ended last call but I’m not certain…

  1. what case it can be???

I know I didn’t show enough data… but I can’t find data… 2. where I can find the logs?
I restarted asterisk and now my phone works well…
but It maybe another phone is in the same problem… in my asterisk.

The normal location for logs is /var/log/asterisk. Logging levels are controlled by logger.conf (normally in /etc/asterisk).

hmmm I can’t restart my asterisk server…

and I use only test server.

In the test server no user so I can’t find logs about this problem.

And I saw a post about 'Everyone is busy/congested at this time (1:0/1/0)'
and I think my problem is same.

In this post he updated the number of channels and increase up to 30.
how I can do it? can you explain me how increase channels and check max channel number?