Asterisk Call Out Error

create a text file

root@local:/var/spool/asterisk/outgoing# emacs -nw /tmp/

put following call data in it

Channel: Zap/g0/09173371425
Application: Playback
Data: hello-world

copy it in /var/spool/asterisk/outgoing folder, then check the log file in /var/log/asterisk/full

I got an error

[Nov 18 13:36:16] NOTICE[20501] channel.c: Unable to request channel Zap/g0/09173371425
[Nov 18 13:36:16] NOTICE[20501] pbx_spool.c: Call failed to go through, reason (8) Congestion (circuits busy)

then I restarted the Asterisk and check log file again.

I found out the following log in startup.

[Nov 18 13:40:35] VERBOSE[20562] logger.c: == Primary D-Channel on span 2 up
[Nov 18 13:40:45] VERBOSE[20562] logger.c: -- B-channel 0/1 successfully restarted on span 2

so I change my call file

Channel: Zap/g1/09173371425
Application: Playback
Data: hello-world

because the log shows that Asterisk starts span 2.then it calls back and plays a hello world sound.