Microsoft Windows Media Resource Kit (Pro-Resource Kit)

The terms unicast and multicast refer to how Windows Media Player receives data from a Windows Media server. In a unicast stream, each Player establishes a one-to-one connection with the server in order to receive a single stream. In making the request, the Player provides its IP address, and the server then directs the stream to that IP address.

Unicast Streaming

A unicast stream can be live or on-demand, and is sent only to the Player that requested it. When the stream is on-demand, the user can control the stream using typical playback controls, such as pause, fast forward, and rewind. The user also has control over when an on-demand stream starts and stops. In a broadcast, the experience is very similar to watching broadcast television. You can tune in and out during the broadcast but have no control over its playback.

Unicast streaming is the most common form of streaming, especially over wide area networks (WANs). However, unicast streaming does have high bandwidth requirements, especially when delivering concurrent streams. If too many streams are being delivered at one time, your available bandwidth will be consumed, and additional users who then attempt to connect will be denied.

Internet Protocol version 6 (IPv6) is a new suite of standard protocols for the network layer of the Internet. IPv6 is designed to solve many of the problems of the current version of IP (known as IPv4) with regard to address depletion, security, auto-configuration, extensibility, and other issues. IPv6 features include the following:

• A new header format, designed to keep header overhead to a minimum by placing non-essential and optional fields after the IPv6 header, and streamlining header processing at intermediate routers.

• Large address space, increasing the address size from 32 bits to 128 bits to support a larger addressing hierarchy and a greater number of addressable nodes.

• Efficient and hierarchical addressing and routing infrastructure, designed to support multiple levels of Internet service providers.

• Stateless and stateful address configuration, enabling hosts to automatically communicate without manual configuration.

• Built-in security, with requirements to support IP Security (IPSec), which provides a standards-based solution for network security needs and promotes interoperability between different IPv6 implementations.

• Better support for Quality of Service (QoS), with new fields in the header to define how traffic is handled and identified.

• Extensibility by enabling additional headers after the IPv6 header, which are only constrained by the size of the IPv6 packet.

IPv6 is expected to be available in Windows Server 2003, but may not be installed by default. You can install it through the Network Connections dialog box on your server. See Windows Server Help and Support for more information. Windows Media Services 9 Series also supports IPv6.

Multicast Streaming

A multicast stream is a one-to-many method of data transmission. In a multicast stream, the server sends one stream to a standard, Class D multicast IP address range (224.0.0.1 to 239.255.255.255). A client subscribes to the multicast by requesting it from an upstream router. That router, in turn, requests the stream from another, and the process is repeated until the request reaches the last router in the chain. That router receives the multicast stream, and then sends it downstream to everyone who requested it.

The benefit of multicast streaming is that only one stream travels the network between the server and the clients, which greatly reduces the amount of network traffic, especially during important broadcasts. No Player ever has a direct connection to the server in a multicast stream, so there is no playback control. The drawback of this scenario is that many networks are not currently configured for multicast streaming. Consequently, most multicast streaming occurs today within LANs. Multicast streaming is not available for on-demand scenarios.