No voice or SIP extension will not ring

Some of the extensions will not ring or no voice after answer.

1: SIP registration fails from time to time, or show UNREACHABLE status even registered.
2: SIP extension rings but no voice after answered. CLI shows
[Jan 23 03:53:29] WARNING[2551]: chan_sip.c:4024 retrans_pkt: Retransmission timeout reached on transmission 62016a9603e0e2d91c784f9a34d35e5c@60.191.0.110:5060 for seqno 102 (Critical Request) -- See https://wiki.asterisk.org/wiki/display/AST/SIP+Retransmissions
Packet timed out after 32000ms with no response

Causes: Cisco firewall blocks SIP by default.

Solution: Remove the blockage from Cisco Firewall. 
Attached:
1: CiscoFW.gif shows the default blockage of SIP
2: sipRegistry.gif shows normal extension status of registration after remove the blockage.

Vidanetwork Technologies, Inc.

Attachments:
CiscoFW.gif
sipRegistry.gif