Tag: RTP

We can protect our voice network with simple Auxiliary VLAN but sometimes to be more secure Auxiliary VLAN are not enough. In this case we can use Security appliances such firewalls or VPN termination devices or both.

Firewall maybe seems like very clean and simple mechanism to protect RTP protocols transmitted voice packets but there’s a problem. Protecting voice networks with a firewall is not so simple because we are not sure what UDP port will be used by the RTP voice packets flow.

If we look at some Cisco network architecture and Cisco device environment, a UDP port for an RTP stream is an random port selected from the pool of 16,384 to 32,767. We surely don’t want to open all those ports on firewall just to be sure that the VoIP will function well. So many open ports may be seen from other side like a bunch of security holes.

RTP (Real-time Transport Protocol)

Application layer protocol RTP is accessible in the TCP/IP protocol suite. Assigned port for this protocol is 5004 and it belongs to the working groups “AVT” and “FEC Framework”. As a standardized packets format, Real-time Transport Protocol (RTP) is used to deliver the audio or video or both on the IP networks. IETF standards association working group of Audio and Video Transport was built up it, at first.

Features of RTP are included end to end communication and data streams transmission in real time manners. But transfer of data to more than one destination is done with the IP multicast support in case of RTP. Moreover, RTP as a primary audio/video transport standard within the IP networks is used along with payload format and connected profile. Today, communication and entertainment systems with streaming media (telephony) are being used it extensively. And some common examples of such systems are such as teleconference applications and television services.