This article is one in a series to assist in the setup, troubleshooting, and maintenance of Cisco Small Business products (formerly Linksys Business Series).
Q. What can I do to resolve one-way audio problem?
One-way audio is usually caused by NAT firewall in the network. On your router, you need to unblock UDP ports 5060, 5061 and port range 16384-16482 by doing Port Forwarding. You might also need to disable "SPI firewall" if there is such function in your router.
In the event that Port Forwarding did not fix the problem you can follow the additional troubleshooting steps below on the SPA962.
Enabling NAT Support Settings
You can set NAT Mapping Enable and NAT Keep Alive Enable to "Yes" under EXT1 tab of the SPA then click .
Alternatively, if the SIP server registering the SPA9XX supports NAT, you can use Outbound Proxy configuration of the SPA to connect to it.
SPA product also supports STUN (Simple Traversal of UDP through NAT (Network Address Translation)) protocol. Under SIP tab, look for NAT Support Parameters. On STUN Server field place your STUN server address, set Substitute VIA Addr and STUN Enable to "Yes ". Place your WAN IP address on EXT IP, then click on .
Note: STUN will not work if you have a symmetric NAT. If you enable the debug through syslog, and set STUN Test Enable" to "Yes " the SPA product will print information about whether or not you have a symmetric NAT.