In situations where a NAT (Network Address Translator) is located between Blueworx Voice Response and the remote endpoints, an additional option known as ‘Symmetric RTP’ is provided. This is to overcome the problem that, when a NAT is placed in the RTP message flow, Blueworx Voice Response needs to send RTP packets to an address within the NAT rather than to the far end IP address and port as specified in the SIP initial negotiation. When Symmetric RTP is enabled (in the Voip DTEA and DTNA Media System Configuration group), Blueworx Voice Response does not transmit RTP packets until it receives a first incoming packet at which time it extracts the source address/port within that packet and, from that point on, transmits all outgoing RTP packets to that address/port (which is likely to be in the NAT/firewall). The NAT translates the source/destination addresses/ports using tables that it maintains internally and forwards the packet to the remote endpoint.
If you experience the problem that audio is only flowing one way, the problem is likely to be due to the presence of a NAT and can be resolved by selecting the Symmetric RTP option in System Configuration.