Multimedia applications (such as RealAudio, VoIP Telephony, Video Streaming etc) were always an issue when passing through a network firewall. These kind of applications behave in unique ways:
- They use dynamic ports.
- They transmit request using TCP and get responses in UDP or TCP.
- They use the same port for source and destination.
- For each multimedia request, the multimedia server might send numerous streams of data in reply.
All the above impose an “unacceptable” traffic behavior for a network firewall, thus multimedia traffic needs some special treatment in order to be permitted through the firewall. [Read more…]