If you'd like to recieve any useful advices you have to provide more details about your setup: equipment list, software versions, network setup.
but anyway, for you the first step is look to the [FAQ] Video conferencing frequently asked questions
Jun 21,2014 Question: What could be causing one way video or one way audio when utilizing video conferencing?
Answer: Please check the relevant release notes or admin guide for your device under the section “Inbound and Outbound Ports” or "Port usage" => here <= in order to open the relevant firewall ports.
Are both ends using the very same configuration on the endpoints ?
The end with only audio has a firewall ?
What about the end where everthing works, whats the network structure ?