Just to share knowledge and close this case 

the problem was due to the size value of this packet which is 1514 byte and it wasn't fragmented well, or never fragmented 

reducing the mtu value of the wan device (home router) solve the case

which led to the necessary   of  reducing sip packet size 

those two tutorials help alot : Thanks Alex Balashov
http://www.evaristesys.com/blog/sip-udp-fragmentation-and-kamailio-the-sip-header-diet/

Thanks All