KENS-TV, Belo’s news and information station in San Antonio, has integrated its IT functions into the television engineering department in order to ensure that every technician is capable of installing and troubleshooting computer- and network-related issues. Image courtesy of Sundance Digital.
Today's digital broadcast systems are increasingly dependent on IT technology. Indeed, the broadcast industry has embraced and used computer systems in a rapid pace over the past eight to 10 years. However, determining what IT network equipment may be best suited and available to improve the workflow at your facility can be difficult. Typically, you will need to rely on vendors for that information. But the more you know about IT technology, the better consumer you'll be. This article will present some basic information to help you in this journey.
IT networks and equipment
There are several resources available to help broadcast engineers better understand IT technology. The EBU/SMPTE Task Force results were published in 1998 and are a good place to start. However, they are more focused on traditional broadcast technology, rather than IT and future technology. Let's get some basic terms defined. Refer to Figure 1 as the starting point for a typical, generic broadcast plant.
Figure 1. Typical IT interfaces and devices in a broadcast plant. Click here to see an enlarged diagram.
Today, the typical goal of using a network is to support the safe and secure transport of content between devices, studios, within facilities or even between continents. The network may provide voice communications, control transmitters, the transfer of data between servers and an editing suite. A network can also be simply for monitoring. The successful operation of a network is based on extensive use of standard interfaces and protocols.
Standard interfaces and protocols
There are many standards and protocols used in today's broadcast and production systems. These standards are typically developed by various industry committees. Some key standards-setting bodies to be aware of include the Audio Engineering Society (AES), Advanced Television Systems Committee (ATSC), International Telecommunications Union (ITU), Internet Engineering Task Force (IETF) and the Society of Motion Picture and Television Engineers (SMPTE). As an engineer, you don't have to wade through long dissertations of standards-setting bodies to understand how they work and where they need to be applied. However, you do need to know how these standards should be applied in building your facility. Fortunately, today's vendors are highly reliable in properly applying the appropriate standards. You may just need to be sure that the various vendors all agree to speak the same standards when it comes to connecting all your devices together. You do not want to find yourself in the position of having to connect divergent equipment together. That is way beyond what most broadcasters have the skills to do.
The backbone of any facility is the network. That network needs to communicate with the devices in a reliable way and at increasingly high speeds. Today, that often means a 100Base-T or higher Ethernet connection. One free piece of advice: Build for higher speeds now, even if you don't need it. While your proxy browser news system may operate fine with a 10Base-T infrastructure, you'll soon find the need to connect devices that require 100Base-T or higher speeds. This means you should build for Gig-E speeds now. Wire is cheap; installation isn't. One good resource on the proper selection and use of network cabling is available at www.belden.com/college/college.htm.
Cat 5 cabling used to be considered standard and sufficient for broadcast interfaces. A Cat 5 cable is rated for 100MHz or 155Mbs, perhaps up to 1000Mbs if the lengths are short. That's not high enough today. If you're going to go to the trouble of wiring a facility, consider using Cat 6 wire. It will support 2.4Gbs. Now, let's look at the basic building blocks.
Figure 2. Shown here is the front door. This bi-directional port may handle either comm traffic only, or comm plus content traffic.
Figure 3. Digital systems need a reference clock. Use one linked to GPS for maximum stability.
Figure 3 shows the network clock component in this conceptual facility. The clock serves to keep all the network elements in time with each other. Never let anyone try to convince you to try to get along without it. Every site in your network needs one. The clock is crucial in not only keeping signals in time, but also to re-sync devices should an error or disturbance in transmission occur. In addition, it's a good idea to lock the clocks to a uniform standard like GPS.
Figure 4. This interface may not exist for some stations. It represents the Plain Old Telephone System (POTS). Click here to see an enlarged diagram.
Figure 4 is probably the simplest device in our facility. It represents the standard telephone connection — plain old telephone service, or POTS for short. If you have a newer IP-based phones, you won't have this element in your system.
Now its time to use the word router. In Figure 5, you will see the router connected to two IEEE interfaces and a virtual local area network (VLAN). This is not the typical cross-point router that broadcasters use to move audio and video between studios and devices, but an IP router. IP routers direct signals based on information contained in the headers of Internet packets using a routing protocol. Consider that an IP router and the typical broadcast router have little in common although they share the same name.
Figure 5. The data and Internet router may connect 802.xx inputs to the station VLAN. Click here to see an enlarged diagram.
All network equipment has to be configured. This can be simple or difficult, depending on the device, the network and the complexity of the task it performs. The configuration of a mid-size router can be complex. To get an idea of the steps that might be involved, go to http://www.ifb.com.pl/~mateo/bgp/ip/2917A-1.html. If you are doing a system-wide install, this can be handled by the system integrator or router installer. However, you will need to identify someone on your staff to be the system administrator to make future changes.
Now we come to the essence of broadcasting, generating the ATSC or MPEG signals for transmission. Today's digital TV plants have multiple SD and HD encoders and decoders. See Figure 6. These devices may have SMPTE 259/292 inputs, and the outputs might be DVB/ASI or Ethernet connections. It's likely they will be linked to an ASI or SMPTE 310 interface to a satellite or terrestrial network facility. The ASI signal may be further formatted to match a standard TDM or Layer 1 baseband transmission facility. It could also be mapped to ATM cells, or IP Packets at Layer 2 or 3. At this stage, it's simply another signal that may need to be routed again before it gets to its final destination.
Figure 6. The compression/decompression modules perform that last-piece interface with both storage and transmission systems. Click here to see an enlarged diagram.
Setting up an IP system starts by port configuration. So what's a port? There are two kinds of ports, physical and virtual. Physical ports are always on equipment. One common physical port is the RS-232 control port. Others include the common IEEE 802.xx or 10/100/1000Base-T ports. Figure 7 is a slightly modified version of the LAN segment diagram, showing one RS-232 port and two IEEE 802.xx ports.
Figure 7. Managing an IT-based broadcast or production system begins by configuring the ports.
Managing IP systems
When considering the benefits of an IT-based broadcast system, it's difficult to argue against the technology. Even so, the changes for broadcast engineers can be difficult and challenging, if not merely because of the new language.
However, the more you know about IT technology, the better qualified you will be to understand what vendors say — and what they claim — not that any vendor would oversell their capabilities. In the end, it's you and your staff that have to use and maintain these new systems, so knowledge is both power and protection.
SMPTE Journal Volume 107, Number 9, September 1998 http://www.smpte.org
“File Interchange Handbook”, Gilmer, Brad, et.al., Focal Press, Burlington, MA, 2003