Streaming Blog

Windows Media Live Streaming Pull vs Push

July 21st, 2005

Windows media streaming allow you to broadcast a live stream in two different ways.

A “Pull stream” consists of the encoding machine running independently of any clients. Once it has started clients can tune in to the broadcast by connecting to the encoder directly on the ip address and port that the encoder is using.

It is possible to restrict access to the encoder by ip address so as to prevent unauthorised users connecting or to prevent the local connections bandwidth supply from becoming saturated, which will lead to buffering and loss of service.

If the encoding computer is behind a firewall or on an internal network then external users will not be able to connect to the stream unless port forwarding is set up and the firewall allows access from an external ip address.

The advantage that a Pull stream has is that if no users are watching the stream, then no bandwidth is used up until someone tunes in to the stream.

Normally Pull streams are used for 24×7 streaming. The encoder restricts access to it’s stream to the ip address of a distribution server. Clients then tune in to the distribution server. The first connection will instigate a connection from the distribution server to the encoder and start running the stream. Subsequent connections will come directly from the distribution server. Once all clients have closed their media players and stopped watching the connection between the distribution server and encoding computer will be closed to save bandwidth and remain in this state until the next person connects to the stream.

A “Push stream” works in a more pro-active way.

The encoder connects directly to the distribution server and sends it’s stream out regardless of if anyone is watching it. Clients tune in to the distribution server and watch the stream directly from there. The advantages of using a Push stream are that the encoder “knows” that the connection has been made and an error will be reported if there is a problem. (With a push stream, as a connection is not necessary you manually have to check that everything is working). The disadvantages of a push stream are that there are the inherent bandwidth overheads of sending out the stream regardless of whether or not anyone is watching the stream. Also at the server side it is a little bit harder to split the log files to create analysis reports afterwards.

Push streams are normally used for short one off webcasts as opposed to 24×7 streaming.

Entry Filed under: Windows Media