Television facilities are gradually evolving and are becoming more IP/networking-centric in many areas. IP networking infrastructure has been built up throughout facilities primarily to handle the exchange of files from one storage device or file-based system to another. Files have been successfully navigating the IP domain within television and playout facilities for some time.
IP networking makes perfect sense for file-based processes, but what about real-time program streams? There are many areas where real-time or linear program streams are in use. (See Figure 1.) Today, we commonly find IP networking used for real-time program streams on the edges of the facility, typically in the incoming feeds area or at the point of outbound transmission. At these points, the stream is encoded and compressed for transport. Take that farther, and here is the killer question: Could IP networking be used throughout a facility?
Headends take an IP plunge
Anyone unsure about the suitability of IP networking infrastructure to carry real-time program streams need only look to the radical transformation that has occurred in cable, DTH and IPTV headends in the past 10 years. (See Figure 2.) In the beginning, these headends would accept a combination of compressed and uncompressed signals, and employed a combination of SDI and ASI infrastructures. Now, these headends have transitioned to using IP networking infrastructures for several reasons. Namely, the signals they transport are now compressed when they arrive and remain so either all the way to the home or, for cable systems that still support analog tiers, are decoded close to the home where the signal is modulated to RF. But, why did TV delivery headends transition to IP?
With the functional integration of devices leading to the development and proliferation of compressed domain splicer systems, the transition to IP was facilitated. Today, traditional MPEG decoders and encoders are being replaced by integrated systems that feature IP inputs and outputs, and combine ad and graphics insertion and transcoding from one compression format to another, or from one bit rate to another, inside a single box. With these integrated transcoder systems, a signal can be demodulated at the entrance of the facility but stay IP until it hits the integrated processing chain. Here, it is internally transcoded, while allowing processing and insertions to take place, thus allowing routing to remain in the IP realm. This integration has allowed the scalability to more channels. Also, it allows for ease of redundancy within a flexible, routable environment, compatible with telecom networking gear already in use there. Having switched the video infrastructure to IP, headends have the ability to share the same infrastructure for TV, telephony and data for Internet services.