NetCache behavior for MMS multicast streaming

About MMS multicast streaming

In a unicast environment, when a client makes a request (clicks an HTTP link) for an MMS stream that is not cached, NetCache connects to the origin server through the default MMS port. In a multicast environment, a live stream request does not result in a connection to the origin server. Depending on the configuration, NetCache responds as described in the following paragraphs.

Multicast in, unicast out:

NetCache intercepts the multicast request at the HTTP proxy and performs an ASX rewrite to insert a special unicast request. NetCache then redirects the request to the designated streaming cache (if it is different) through the default MMS port. NetCache fetches the .nsc file, decodes it, and begins to receive multicast data from the media server.

For example, the original ASX request (initiated through a browser) is as follows:

http://web-server/foo.asx

The original ASX response is as follows:

<asx>

 <ref href = "http://web-server/foo.nsc">

<asx>

After the ASX rewrite, the MMS request is as follows:

<asx>

 <ref href = "mms://cache-ip/?http://web- server/foo.nsc">

 <ref href = "http://web-server/foo.nsc">

<asx>

Unicast in, multicast out:

NetCache intercepts the multicast ASX response that redirects the subsequent .nsc request to a streaming server. NetCache assigns a new multicast channel (IP address and port) to this multicast request and modifies the .nsc response to reflect the new IP address and port number. NetCache then connects to the media server using the unicast URL embedded in the .nsc file and broadcasts the multicast stream.

For example, the original ASX request (initiated through a browser) is as follows:

http://web-server/foo.asx

The original ASX response is as follows:

<asx>

 <ref href = "http://web-server/foo.nsc">

<asx>

After the ASX rewrite, the response is as follows:

<asx>

 <ref href = "http://cache-ip/web-server/foo.nsc?">

 <ref href = "http://web-server/foo.nsc">

<asx>

Multicast Output Only

When this option is enabled, all streaming clients are forced to access live streaming content using the multicast protocol. You should enable this option if you want to ensure that only multicast delivery is used for live content streamed over your network.

Note
The Multicast Output Only option limits only client-side traffic to multicast transport. The server-side transport can be unicast or multicast.