Iax question

[size=150]hi all,
i’m a new in asterisk world. i installed it and when i configure kiax sophtphone in iax.conf it’s work correctly but that i have one problem:
kiax phone change it’s status after short period of time .
this is the the output on asterisk system:
[Jun 7 10:47:25] NOTICE[7923]: chan_iax2.c:7873 __iax2_poke_noanswer: Peer ‘105’ is now UNREACHABLE! Time: 4
[Jun 7 10:47:55] NOTICE[7921]: chan_iax2.c:7079 socket_process: Peer ‘105’ is now REACHABLE! Time: 8

why this occur ,how can i fix this problem and let kiax work correctly without fail?[/size]