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By Joe Gaucher, ClearBand LLC

A thin-client-based, multicast-enabled system streaming media system provides numerous benefits for operators that deliver video via Internet protocol (IP).

Years ago, operators learned that although video delivery to more than one TV set held occasional technological challenges, it yielded satisfied customers. Today, the ability to deliver live video to a new range of IP-enabled screens in the home and business is supported by both technology standards and a real business case. These new screens run primarily on personal computers (PCs), but the latest digital set-tops soon will bring IP video to the television.

The simultaneous delivery of high-quality, live digital video to PCs and TVs will become a key component and service differentiator on the broadband scene. The capability also is a new tool any broadband provider of bundled video and data services may use to drive the acquisition of new customers and increase revenues. Offering high-quality subscription video via IP to broadband subscribers is a fairly new concept. What is the technology involved in the delivery of this service?

Scalable and upgradeable

Today's competitive environment calls for unprecedented flexibility. Rather than proprietary methods, globally accepted standards, such as those developed by the Moving Picture Experts Group (MPEG), should be used. Rather than relying on hardware-based encoders and decoders, a completely software-based solution for encoding, streaming and decoding high-quality, IP-based video over a hybrid fiber/coax (HFC) network is desirable. Finally, the system should integrate seamlessly into existing broadband networks.

Toward this end, digital video systems that use standard IP transport have been developed that are compatible with qualified cable modem termination systems (CMTSs) and allow software-based decoding on a standard Pentium-class PC (see Figure 1). With these systems, streaming rates may vary from a few hundred kilobits per second (kbps) to several megabits per second (Mbps), allowing for a wide range of video quality levels to suit the needs of the operator.

In the headend, IP-based digital video systems gather programming before converting the signal to IP for delivery over the same HFC plant used for cable Internet customers. The server platform of choice is a multiprocessor, Pentium-class server running the Linux operating system, but the system should be flexible enough to be configured for other platforms.

A system should have the flexibility to accept either an uncompressed live video channel or a pre-encoded digital file. With a live channel, the server digitally compresses (encodes) the video and audio and immediately streams the channel over the network using the IP multicast method. In the case of a digital file, the system should be capable of transcoding to a different bit rate and then either broadcasting or storing the stream for delivery at a later time. Video may be sourced from any of the usual methods: camera, DVD player, satellite link and so on.

It is highly desirable that you choose a system that uses an open standard--such as MPEG-2 or MPEG-4--for encoding the video and audio. MPEG-2 is the encoding standard of choice because of its excellent performance and worldwide acceptance by the digital cable, satellite and high definition television (HDTV) industries. The chosen system also should have the flexibility to facilitate new standards, such as MPEG-4, easily and as they are ratified. MPEG-4, in particular, offers some promising enhancements for video streaming, and several companies, including ClearBand, Cisco Systems, PacketVideo and AOL Time Warner, are working toward ratification as members of the MPEG-4 Industry Forum.

Multicast video delivery

Most traditional Internet applications, such as Web browsers and e-mail, operate between one sender and one receiver. During traditional video streaming over the Internet, individual streams are unicast from the server to the user. New applications are advancing traffic handling to help overcome Internet bottlenecks.

IP multicast--an extension of IP--is an efficient, standards-based solution for broadcasting video and audio over broadband networks. Here is how it works: a video file or live channel consisting of digital video packets is encapsulated into an IP stream that is addressed to a "group" of users. The service provider's network distributes the stream to all the members in the multicast group. Because the goal of most video applications is to have as many users watch a program as possible, broadband operators should select a system that uses IP multicast for the transport mechanism. IP multicast offers the highest quality service to the largest number of simultaneous customers using the least amount of network resources.

Unlike the typical point-to-point transport of the Internet, in which individual files are streamed to each PC, a multicast stream is delivered to all users simultaneously. Instead of delivering 1,000 video streams to 1,000 users--which would overload the most modern network--this one-to-many form of transmission allows service to all 1,000 subscribers with one stream. Instead of flooding the system with 1 Mbps streams for 1,000 users, it is necessary only to devote a single 1 Mbps stream for 1,000, 10,000 or 100,000 users (see Figure 2).

Consider it a broadcast solution for the wired world. Just as over-the-air broadcasts are available to anyone with a receiver, multicasts are available to anyone with the proper decoder and authorization. For a more detailed look at how multicasts are accomplished, see the related sidebar.

A thin-client application

On the decode side, the broadband user ideally should have an easy-to-use interface from which to choose the video he or she wishes to view. The streaming system should not take substantial memory or require a lengthy installation. Finally, system upgrades should be transparent to the user, and not require the installation of new versions of software going forward.

Unfortunately, the architecture of 'old-school' streaming systems relies on each user to download in advance a large player application and install it onto his or her hard disk. Developed primarily for narrowband streaming of video over the 'open' Internet, these streaming programs inevitably become out-of-sync with the version of software used to encode the video streams, and thus the subscriber faces perplexing error messages and the requirement to download a new version before watching the video.

With an operator-controlled, thin-client architecture, these software-versioning issues don't exist. Each time a user selects a channel to watch, the operator's server will transmit a fresh copy of the thin-client viewer. The viewer should have a small footprint (well under 1 MB) so that it is delivered in just seconds over the broadband network. It should reside only in active memory (random access memory, or RAM), and disappear when the user is finished viewing.

As new versions of the software are released, operators need only update the servers at the headend, and users will immediately begin to take advantage of the enhanced features in their home or office, again without the need to install or reconfigure. Because of latency requirements, this approach is only viable over a broadband network.

Further requirements include the ability to watch multiple streams, scalability of the viewing window and transportability to other decoding platforms. The ability to launch multiple viewers simultaneously should be an option, allowing consumers to view several streams coincidentally. The viewer size must be scaleable, allowing the user to operate other applications at the same time they are viewing video.

Finally, a thin-client application is an ideal approach for the set-top market, particularly today's digital set-tops that have little or no hard drive space. Many of the advanced digital set-tops now have added support for IP and can decode IP-delivered MPEG-2 content.

Conditional access

While the beauty of an IP-multicasting video system is that multiple users may watch the same stream, in some instances--for example, with pay-per-view (PPV)--a stream should only be viewable by some of the users on an IP network. The operator should carefully examine its requirements for conditional access (CA). In an enterprise network, circumstances exist where only certain employees should be able to view the CEO's speech. In a cable operator's network, only those subscribers who have paid for the PPV concert should be able to watch it.

An effective CA system should be able to allow or deny viewing by individual users on a channel-by-channel basis. To offer services such as PPV, you need to allow service on a program-by-program basis within the same channel. The conditional access system should use advanced digital encryption techniques, with randomly changing encryption keys to safeguard valuable video content.

The operator-controlled, thin-client approach provides an inherent conditional access system for the broadband operator because it may include the decryption algorithm and key(s) for decrypting the stream(s) associated with it. Only PCs with the correct thin-client viewer are able to access the encrypted stream, and the only way to obtain the viewer is to register as an authorized user. Providers may easily configure the system to validate users to ensure they are subscribing to the appropriate service tier.

While the delivery of a high-quality, multicast video service is limited to a broadband network, it is important that the system an operator chooses be controlled remotely by authorized administrators.

Using any Internet-enabled device at almost any location, administrators should be able to do everything from scheduling content for playback to categorizing it by type, rating, bit rate and other parameters. It also should be possible to add or subtract IP multicast channels, update the electronic programming guide and control multiple systems from different locations.

One way to achieve this management software is by using a Java-compliant implementation. Such a system may allow numerous network administration levels that provide appropriate access to various employees, enabling a true end-to-end content management and distribution system.

The system also should be adaptable for integration with numerous other headend, automation and management systems, to enable participation in fully automated system operation. Facilitated links to billing systems, provisioning, activation, customer service software, customer profiling and data mining packages and other applications should be integrated into the software to simplify network operations and improve marketing and bundling efforts.

An IP future

For broadband cable networks, the future is IP. Today, high-speed cable modems use IP to communicate. Cable telephony systems are rapidly moving from digital circuit-switched protocols to voice-over-IP (VoIP). The final service to move to IP will be digital video. Once this move occurs, broadband operators will enjoy benefits ranging from lower costs from shared infrastructure to greater bandwidth efficiency. In other words, data, voice and video services will be able to intermingle over the same frequencies and on the same equipment. Even the set-top vendors--such as Motorola, Scientific-Atlanta, Sony and Pace--are seeking to expand into a centralized home gateway overseeing the traffic flows of numerous devices in the home, with IP as a core technology.

Joe Gaucher is chief technology officer for ClearBand LLC. He may be reached at .

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