Multicast streaming is a one-to-many relationship between a
Windows 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 the
IP address. All clients receive the same stream. 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. Using a multicast stream preserves network bandwidth and
can be useful for low bandwidth local area networks.
You can deliver content as a multicast stream only from a
broadcast publishing point. In addition, your network routers must
be multicast-enabled, meaning that they can transmit class D IP
addresses. If your network routers are not multicast-enabled, you
can still deliver content as a multicast stream over the local
segment of your local area network.
The following figure shows an example of content being
distributed from an encoder as a multicast stream by using a
broadcast publishing point.
These steps describe one way you can multicast live content from
an encoder, as shown in the previous figure.
Send the live images from a digital video camera to a video
capture card on a computer running Windows Media Encoder. The
images are encoded into Windows Media Format, and then streamed to
the server using HTTP.
On the Windows Media server called Server1, use the Add
Publishing Point Wizard to add a broadcast publishing point that
sources from the encoder. As part of the wizard. you may choose to
allow unicast rollover. Unicast
rollover ensures that players that cannot access the multicast
stream can still receive the content by switching to an available
unicast stream. For example, a player may be unable to access the
multicast stream if the network routers are not multicast-enabled,
or if the player is beyond the time-to-live (TTL) radius of the
Use the Multicast Announcement Wizard to create an announcement
to provide users with the URL to the content. The wizard can create
a multicast information file (with an .nsc file name extension), an
announcement file (with an .asx file name
extension), the code necessary to embed an announcement within a
Web page, or any combination of those three options.
Multicast streaming and the WMS Multicast Data
Writer plug-in are available only if Windows Media Services 9
Series is running on the following editions of the operating
system: Windows Server 2003, Enterprise Edition and Windows Server
2003, Datacenter Edition. If you are running Windows Server 2003,
Standard Edition, these features are not supported.