The Problems of Firewall/NAT Traversal: The purpose of a firewall is to ensure that only authorized users are allowed Access. Today, most homes possess a firewall-protected connection through cable or ADSL.
Enterprise or home users who are protected behind their own firewall are Communicating from what we call an internal network. The user's endpoint communicates with a gatekeeper via the Internet through a firewall or a NAT (usually both) to another endpoint. The gatekeeper and the other endpoint are on what we call an external network. When the other endpoint is on a different internal network, it should also use a similar solution to traverse through its own firewall/NAT.
For that video communication we are going to user RTP,RTSP etc Protocols. These protocol are used to transmit the audio, video for A to B.
RTP is unidirectional
-A indicates IP/port to receive from B
- B indicates IP/port to receive from A
- If either is behind NAT, media won't flow to them.
So we have only achieved the point to point Audio, Video transmission using RTP Streaming Protocol. In the case If we want to send behind NAT, Solution: make RTP look like client-server protocol
- A indicates IP/port to receive from B
- B sends to A, A sends back to B using source IP/port of RTP
- Basically, only need IP address from ONE of the participants - the "server"
For our web based application, some time the presenter (A) or Client (B) may be use the Proxy server setting to access the Internet. So we need the solution for Transmitting Audio, Video - (using of Streaming Protocol) and Data - (TCP, UDP protocol) over NAT, Firewall.
To achieve the NAT Traversal there has a two simple algorithm, which are popular
1) STUN - Simple Traversal of UDP (User Datagram Protocol) through NATs (Network Address Translators)
2) TURN - Traversal using Relay NAT
3) Universal Plug and Play (UPnP)
4) Application Layer Gateway
5) Tunnel Techniques
6) Automatic Channel Mapping(TM) (ACM)
7) Manual Configuration
In the Above methods the STUN is the best method of solving NAT. The is a API called STUN in JAVA.This will help us to Solving of NAT Traversal Problem. STUN is a client-server protocol. A VoIP phone or software package may include a STUN client, which will send a request to a STUN server. The server then reports back to the STUN client what the public IP address of the NAT router is, and what port was opened by the NAT to allow incoming traffic back in to the network. The STUN algorithm as follows,
For that Video, Audio Transmission we need the streaming Server like Microsoft, Real Media, Apple Quick Time, Flash Media server, etc. The main reason for using Steaming server is Transmitting and receiving for RTP Stream Data. For Transmission of Data we use the TCP or UDP Sockets.
The IP based voice and multimedia services as major part in the Internet traffic. Unfortunately, a number of technical problems are having. The most significant of these is to provide secure connection to subscribers behind NAT (Network Address Translation) devices and Firewalls.
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