Streaming with a Web Server: the Advantages
There is really only one major advantage to streaming with a Web server rather than with a streaming media server—utilizing existing infrastructure. Because the Web server approach uses only the standard Web server--that presumably already exists in the organization—no new software infrastructure need be installed or managed. The Windows Media server approach, on the other hand, requires the content producer and/or the systems administration staff to install and manage additional server software. This can result in incremental training and staffing costs to learn and manage the more complex, but also more powerful, Windows Media server environment.
It is important to note that the increased load that Web server-based streaming puts on existing Web server infrastructure often results in the need for additional Web server hardware to service the client requests. Choosing Web server streaming over a dedicated streaming media server based on hardware cost alone usually does not result in any financial savings.
Streaming with a Windows Media Server: the Advantages
Designed specifically for the task of delivering live or on-demand streaming media rather than many small HTML and image files, a Windows Media server offers many advantages over standard Web servers.
- More Efficient Network Throughput. We've already mentioned one of the main advantages of Windows Media server streaming—the ability to use UDP, the specialized protocol optimized for live and on-demand streaming. The TCP-based transfer used in Web server streaming is designed to repeatedly drive the slowest network link (likely the 28.8 Kbps modem link) to packet loss. This wastes bandwidth by: (i) re-transmitting data to replace the lost packets; and (ii) under-utilizing the network link while re-estimating the throughput that can be supported by the network connection.
The UDP protocol allows higher bandwidth to be delivered to the client (resulting in better video quality), even when assuming the same network connectivity between server and client and the same level of congestion on the Internet. By having a specialized streaming media server, we know what rate the data is going to be consumed, based on headers of the compressed media file. The Windows Media server sends data to the client (Windows® Media Player) only at this required bit-rate, and it doesn't drive the bottleneck network link to loss. Thus the network throughput is better, resulting in better quality audio and video for the client. - Better Audio and Video Quality to the User. Better network throughput is only one of several ways that a Windows Media server delivers superior audio and video quality for users. Here are two more examples:
- Because the Windows Media server and the Windows Media Player remain in contact throughout the play interval, the server can dynamically respond to client feedback. If network congestion is allowing only 22 Kbps of data to reach the client (instead of 28.8 Kbps), the server can decide to retain the audio quality but slightly lower the frame rate of the video stream so that it doesn't overshoot the available 22 Kbps. This ability is not possible with the Web server approach. In a Web server scenario, with no feedback from the client and no ability to dynamically prioritize audio over video, the audio/video delivered by a Web server would be stop-and-go at the client, causing the insidious "rebuffering" delays common to early implementations of streaming media. In contrast, the Windows Media server provides a continuous, smooth stream with barely perceptible changes in video frame rate during periods of network congestion.
- Streaming with a Windows Media server takes advantage of UDP's inherent higher priority over HTTP traffic to give the streaming audio and video data higher priority than file and Web page transfers. This increases the likelihood of uninterrupted viewing.
- Support for Advanced Features. The Windows Media server approach supports such advanced features as detailed reporting of streams played, VCR controls (seek, fast-forward, rewind), live video delivery, and delivery of multiple streams to the client. With Web server streaming such features, if they are even possible, are difficult to implement and inefficient to support.
- Cost Effective Scalability to Large Number of Users. In the early days of streaming media, deployments often needed to serve only a small number of users simultaneously, making Web server streaming an adequate solution. But as delivery of audio and video has increased, sites often serve hundreds or thousands of simultaneous users. In these situations, two key capabilities of the Windows Media server provide increasing advantages over a Web server:
- Specialization. In the Web server approach, the Web server is used to deliver the media files to the client. Web servers, however, are optimized for delivering lots of small HTML files, not large media files. With high volumes of file requests, a Windows Media server greatly improves performance by optimizing how media files are read from the disk, buffered in main memory, and streamed onto the network. A Windows Media server can easily improve scalability by a factor of 2 to 3 over a Web server.
- Multicast Support. One way to get live or stored audio and video to large audiences with minimum network congestion is to use multicast networking technology. Multicast allows a single media stream to be played simultaneously by multiple clients, drastically reducing bandwidth use. Only a specially designed streaming media server, such as a Windows Media server, has this capability.
- Protection of Content Copyright. Because Web server streaming creates a local cached copy of every media file played, there is no way to prevent end users from copying the files to a personal directory for later viewing. This hurts content providers who have a pay-per-view business model, or who have an advertisement-based revenue model, as the end users need not visit their site repeatedly. With a Windows Media server, users can only stream data and are prevented from downloading the file directly to their hard disk. As data packets are received over the network, they are delivered directly to the client application with no easy way for the end user to intervene and make a copy.
- Multiple Delivery Options. With a Windows Media server, the media may be streamed with the optimal UDP or Multicast protocols when possible, and streamed with the TCP protocol when necessary. This enables corporate users to view Internet content without compromising firewall security and ensures that all users on all networks can access all streaming media content. The Windows Media server implements its own version of the HTTP protocol to enable streaming through a firewall or proxy server while still retaining most of the advantages a Windows Media server.
Windows Media Services support four different protocol configurations, each offering specific benefits.
- UDP – As detailed in the Windows Media server section, UDP provides the most efficient network throughput and can have a very positive impact on the user (player) experience. The only downside to UDP is that many network administrators close their firewalls to UDP traffic, limiting the potential audience of UDP-based streams
- TCP – As detailed in the Web server section, TCP provides an adequate, though not necessarily efficient, protocol for delivering streaming media content from a server to a client. As customers often open the TCP ports in their firewalls, Windows Media Services can use the TCP protocol enable streaming media to flow through these firewalls, which often block UDP traffic.
- HTTP + TCP – The Windows Media server can also support HTTP-based control commands along with TCP-based data delivery. This combination has the benefit of working with all firewalls that let Web traffic through (port 80) and provides much more control (fast forward, rewind, etc) than a standard Web server, but also adds some overhead to the raw TCP stream that decreases scalability.
- Multicast – The Windows Media server can also support IP Multicast protocols to allow very efficient delivery of streaming content to large numbers of users. Multicast enables hundreds or thousands of users to play a single stream, but will only work on networks with Multicast-enabled routers. Multicast is becoming prevalent on corporate networks, but is still very rare on the Internet.
The Windows Media server will automatically switch to the appropriate protocol so no client-side configuration is necessary. The server will initially attempt to transmit files using the optimal UDP or Multicast protocols. If unable, the server will then attempt to send first via the raw TCP protocol, then via TCP with HTTP-based control.
Tidak ada komentar:
Posting Komentar