Unavailable telephones

Hi

I have a problem with telephones, namely they are unavailable periodically.
In my Asterisk console I have below reports:

[Apr 23 10:54:40] NOTICE[21641]: chan_sip.c:15373 handle_response_peerpoke: Peer ‘234’ is now Lagged. (2014ms / 2000ms)

[Apr 23 10:54:50] NOTICE[21641]: chan_sip.c:15373 handle_response_peerpoke: Peer ‘234’ is now Reachable. (58ms / 2000ms)

In my telephones and gates, options: Register Expires is 60
How I can resolve this problem?

Regards
Jack

Turn off “qualify” in sip.conf, or fix the underlying network reliability problem.