Video networks
Mar 1, 2010 12:00 PM, By Thomas Heinzer
Solutions-based technology uses legacy infrastructure and readies networks for the future.
Figure 1. IP networks can be used for contribution and distribution.
Select figure to enlarge.
Much is expected from today's video networks, and broadcasters and telecommunications service providers face a range of challenges. Multiple formats, from fiber to SONET/SDH and now IP, a myriad of networks and rapidly evolving video networking technology are just the beginning. The increasing bandwidth needs of HD coupled with requirements for higher-quality signal transport stretch the capacity of existing networks. Exciting new applications such as telemedicine require the very highest-quality and lowest-latency transmissions, and the global nature of today's major events require seamless, real-time signal transport over ever-increasing distances, often through existing fiber infrastructure. It is possible, however, to build upon existing networks to meet these challenges and more without wholesale network replacement.
As always, there is not a single solution. The answer lies in building a network that is flexible, scalable and cost- and resource-efficient. Strategic planning, a systems approach and standards-based technology can maximize existing networks and provide a surprising degree of future-proofing. Solutions-based technology can allow the use of legacy infrastructure while ensuring maximum bandwidth for HD and preparing a network for the video-over-IP future. The benefits of using one universal network for Web functions such as e-mail as well as content, video and voice communication are undeniable.
Video over IP: the paradigm of the future
Not many will argue that all signs point to a video transport future dominated by IP. (See Figure 1.) What is seen as the ultimate mode of transport that so nicely dovetails with our digital age poses problems for professional, contribution-grade video transport. First, departure from traditional point-to-point video transport methods causes discomfort for broadcasters. IP is, by its nature, imperfect. It was created with high tolerance for error to maintain connectivity in extreme emergencies. It followed a “best effort” principle. Your packets will get there — probably. What was gained in agility and flexibility for asynchronous communication was lost in stability for highly time-sensitive transmissions such as video. Broadcasters and telecommunications service providers have been accustomed to ensuring safe signal delivery by using large bundles of coax cable with a clear path for each signal and infrastructure for real-time monitoring and control that was decades in the making. With IP, that 8in cable bundle was replaced by a Cat 5 cable and a feeling of “where did my signal go?” Packetizing and trusting content to an IP network meant losing vital management and control infrastructure and flying blind.
Despite trepidations in the professional video broadcast community, we are now entering a time when the benefits of IP and the technology to meet its challenges have converged. IP's physical infrastructure is a gift from the Internet revolution that can now be manipulated to deliver content the way broadcasters need it to. Instead of complex, expensive installation of special-purpose cabling and routing for video networks, IP equipment provides economies of scale. IP already is well-established in some areas; at the distribution level, set-top boxes are all IP-based. It's also coming to primary distribution, and soon on its heels will be contribution. IP offers flexibility with point-to-point video connections and switching replaced by IP addresses. IP can also provide maximum use of network capacity.
For all of its benefits, the limitations of IP are well-known, but technology now exists to meet the challenges of carrying professional-grade video over IP networks. Visual quality and latency are significant hurdles, yet the right products correctly implemented and integrated prevail over these hurdles. Forward error correction (FEC) ensures that the encoded video streams can be reconstructed if there is any packet loss; synchronization can be assured; and transport stream structure ensures continuous, real-time monitoring and analysis of any payload in the transport stream chain. There are comprehensive and standards-based multichannel systems for monitoring the integrity of transport streams, so broadcasters and telecommunications companies can demonstrate SLA-compliance, identify error sources, reconstruct intermittent error conditions and handle multiple protocols and combined signals.
Flexible, scalable transport streams
Another characteristic of a successful video network is the use of a transport stream structure. Transport streams provide an ideal way to carry video, allowing the control and monitoring of signals and video integrity at every step. As IP is adopted at different rates in different countries, and even across different market segments within the same country, underlying transport stream technology will provide a smooth migration. A transport stream is comprised of one or more packetized and multiplexed compressed video signals and their associated video along with program descriptors and other data, which together enable manageable mapping into video or telecommunications networks.
Transport streams may have simple or complex programs. Indeed, the flexibility of transport streams to carry wide-ranging signal sizes is one of its greatest advantages. Transport streams carry compressed signals of any kind (MPEG-2, MPEG-4, H.264, JPEG2000) while also providing the ability to multiplex or remultiplex to create new bundles of programs. This has enormous positive implications, because a transport stream that has been encapsulated over Ethernet retains the information required for control and monitoring that is lacking in video mapped directly onto IP. And once in the transport stream domain, interchange between IP, SONET, fiber, satellite, terrestrial, cable, microwave and wireless networks is possible, because there are standards for mapping to each of these transmission media.
Because transport stream structure allows scalable payload, hardware infrastructure does not have to be added to transport offices and studios. This saves investment and resources and goes a long way toward cost-efficiency. The flexibility afforded by transport streams allows the use of legacy infrastructures, perhaps one of the most important advantages of transport stream. Once in their packetized form, signals may be moved across any network structure. Transport streams allow multiplexing in a myriad of ways, carrying important timing and program information that allows different devices to add, drop or pass videos at will. Video networks initially deployed for MPEG-2 can be used for more advanced transport technologies. And now, with visually lossless JPEG2000 compression available for contribution networks, the benefits of MPEG-2 transport streams for JPEG 2000 are critical. International standards bodies are now at work to establish this standard. Once adopted, this standardized method will guide the transport of production, contribution and distribution material. And once in a transport stream, content may be mapped from SONET/SDH to ASI, IP, QAM, QPSK, etc., regardless of content specifics. Likewise, we can protect with transport stream switching and FEC, monitor and measure with ETSI 101-1290 equipment and multiplex, filter and store using the standard methods developed for MPEG-2.
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