voice troubleshooting case debrief-call drop after 5 mins

Topology
IP phone > Cisco CallManager > H.323 Voice Gateway > Public Switched Telephone Network (PSTN)
Symptom:
PSTN calling IP phone gets dropped after 5 minutes.

Problem description:
CCM and H323 has keepalives sent between them, 1 every minute, after the 4 keepalive is missed, call will be dropped.

The messages below are the output of “debug isdn q931” and “debug ip tcp transaction”:

Mar 16 19:45:17.966: TCP0: keepalive timeout (1/4)
Mar 16 19:46:17.966: TCP0: keepalive timeout (2/4)
Mar 16 19:47:17.966: TCP0: keepalive timeout (3/4)
Mar 16 19:48:17.966: TCP0: keepalive timeout (4/4)
Mar 16 19:48:17.966: TCP0: state was ESTAB -> CLOSED [40523 ->
192.168.17.244(1720)]---CCM IP address
Mar 16 19:48:17.966: TCB 0x46666038 destroyed
Mar 16 19:49:13.478: ISDN Se0/2/1:15 Q931: RX <- DISCONNECT pd = 8
callref = 0x0201
Cause i = 0x8090 - Normal call clearing
Mar 16 19:49:13.478: %ISDN-6-DISCONNECT: Interface Serial0/2/1:9
disconnected from 01085155315 , call lasted 415 seconds
Mar 16 19:49:13.482: ISDN Se0/2/1:15 Q931: TX -> RELEASE pd = 8 callref
= 0x8201

They indicate that after 4 keepalive packets are missed between the
Callmanager server and the voice gateway,the call gets dropped.

Fix:
disable the Trend Micro firewall service on the Cisco CallManager server