SIP load balance issues

Dear all,

I have some POC case with my customer and I have question about SIP load balance, but I'm not well about SIP. Currently I can create VS to load balance SIP servers but still have some issue from my customer below.

(1) my customer test simulate to flood call to VS(SIP serves) but only few call connection(25 Call-per-Sec) then F5 will not response anything. But when he tried with direct connection from client to SIP server, it can flood more than 200 Call-per-Sec.

(2) when my customer test simulate call flow via F5 for the first connection likes REGISTER, INVITE, Ringing, Call. But when the last connection likes BYE it didn't pass F5, it direct between both of client and SIP server.

Remark: file reference below (for sniffer file and ucs file)

http://www.mediafire.com/download/ewr1z85isa8smai/dump_09_test_flood_sip.rar

http://www.mediafire.com/download/lc4av7g78xfvcac/backup_config.rar

Best regards,