Multicast streaming is a one-to-many relationship between a media server and the clients receiving the stream. With a multicast stream, the server streams to a multicast IP address on the network, and clients receive the stream by subscribing to that IP address.
Because there is only one stream from the server regardless of the number of clients receiving the stream, a multicast stream requires the same amount of bandwidth as a single unicast stream containing the same content, thus increasing network efficiency. However multicast requires hardware support from the network infrastructure and its benefits are usually limited to local area networks as data sent to a Multicast IP is not forwarded by routers, gateways and firewalls (unless they are specifically designed and configured to do so, but these are rare, specialized equipment).
By default, in an ION encoder, all outgoing media streams are assigned a Multicast IP address, a Multicast port and a Multicast TTL. From the web management interface or from the ION API, the user can set the start IP, start port and TTL. To disable multicast streaming, the user can simply set the multicast start port to 65535.
Based on the multicast settings described above, the ION encoder will automatically assign Multicast IP and Multicast port for each of its outgoing streams that are active. The user can see what the encoder has chosen from the Configuration
section, Video In > Video Compression
The client decoder can access this stream by using RTSP. If configured properly, during the setup phase, the decoder will first ask for the multicast stream from the encoder. If multicast is not enabled on the encoder, the decoder will revert to a unicast connection to receive the stream.
If the client wants to connect directly to the RTP stream, without invoking the RTSP dialogue, a P2P connection must be enabled on the encoder, so that it “pushes” the RTP stream to the Multicast IP.