Connection fail between ITSP's proxy server and my asterisk

I wanna connect proxy server.

my IP Phone -> my asterisk -> service provider’s proxy server -> extern PSTN phone

but asterisk server can’t register to proxy server.

I think that configuration is right.

When asterisk send to register request, proxy server don’t response.

I did capture packet. but no response.

MY setting

sip.conf

[kms]
username=kms
type=friend
secret=1111
host=dynamic
nat=yes
qualify=yes
callerid=0134

register => 070XXXX0134:password@proxy.SP.co.kr:5060/0134

[my-out]
type=peer
host=SP’s proxy IP
username=070XXXX0134
secret=password
fromuser=070XXXX0134
fromdomain=proxy.SP.co.kr

extensions.conf

[default]
exten => _X.,1,Dial(SIP/${EXTEN}@my-out)

If lines provided is not a form of trunk, can’t my asterisk server connect to proxy?
I could connect my IPPhone to proxy directly.
but asterisk not.

perhaps you have a firewall issue and the return SIP signaling is being blocked?