4.6.2 Sequencing for Broadcast Content Delivery
The following sequence occurs when a client is requesting broadcast content. A proxy server handles requests and content delivery between the client and the origin server that generates the broadcast.
The proxy server comprises a server role and a client role. In the following description, the client that connects to the proxy server is referred to as the media player client to keep it distinct from the client role of the proxy server:
The media player client sends a Describe (section 2.2.7.2) request.
The higher layer of the proxy server checks whether it has a client role that is currently receiving the content. If the content is not being received by any client role, then the higher layer of the proxy server creates an instance of the client role and uses it to open a connection with the origin server. These steps are described in section 4.6.3.
The higher layer of proxy server checks whether the content can be split, as determined by the x-wms-proxy-split directive on the Cache-Control (section 2.2.6.2) header that is provided by the client role. If the content cannot be split, and using the current client role would cause the content to be split, then the higher layer of the proxy server creates another instance of the client role and uses it to open a connection with the origin server. These steps are described in 4.6.3.
The server role of the proxy server sends a "200 OK" response that includes the SDP record and the Cache-Control header, as specified in 3.2.5.4.
The media player client sends a SelectStream (2.2.7.10) request using the Setup method for each selected stream.
The server role of the proxy server sends a "200 OK" response to the media player client, as specified in 3.2.5.6.
The client role of the proxy server communicates any subscribed-to events to the origin server using the SendEvent (2.2.7.11) request, as specified in 3.1.4.7 and 3.1.4.9.
The media player client submits play statistics using a LogPlay (section 2.2.7.7) request.
The server role of the proxy server responds with "200 OK", as specified in 3.2.5.12.
The following illustration shows the sequencing that occurs when the media player client requests broadcast content from a media server that is configured as a proxy server.

Figure 22: Broadcast content delivery