Routing Technology

During the last decade, a full range of technical solutions for digital broadcast and production has emerged, and it has materially changed our industry.

Distribution amplifiers like those shown here are integral to an efficient routing system. Often, the DAs will take up more rack space than a modern router.

But, while some digital technology offers cost savings or new features, much of the technology implemented during this revolutionary period simply replaced the analog versions, function by function. Perhaps the only type of technological progress that does not fit this mold is the substantial innovation in routing technology.

Then and now

Routing, in the first 50 or so years of the video industry, was confined to connecting analog signals in a variety of interconnect formats. Most important are the NTSC and PAL analog composite single-wire interconnects, though component analog signals have been important in many applications. But component analog was implemented to a lesser degree, and thus received less attention in the design of new and innovative routing systems. Standing out from that crowd are applications for high-quality graphics, high-end compositing and wide-bandwidth display for large venues. Those requirements are very much alive. Suppliers who traditionally have concentrated their efforts outside broadcast technology have a significant share of the market for wideband analog systems in these venues.

Today, the routing landscape includes those applications, as well as digital implementations in the more traditional television (i.e., broadcasting) space that span a wide range of needs. We have also seen a proliferation of both very large and very small systems for a panoply of applications.

The emergence of SMPTE 259M facilitated much of the explosion in routing technology. The ability of 259M to handle multiple standards, as well as to act as a high-speed data transmission path, are key dynamics in the changes in routing technology. Similarly, the development of AES facilitated the design and deployment of audio routing (though initially AES was closely focused on audio production and recording markets). There are other forces that are equally important — forces that shape the range of applications for which routing is used and the way it is implemented. They will shape future routing evolution as well.

Controlling and monitoring

One aspect of routing that has seen dramatic changes is the control system. Early analog routers used discrete wiring to enable crosspoint selection, which limited the control panels to short distances. By the '70s, serial communications over coax and twisted pair took over and allowed the control-panel distances to increase dramatically.

Large installations require careful attention to cabling plans.

RS-422 communication became the favorite of a number of manufacturers partly because of the balanced nature of the RS-422 signal and its ability to transmit over longer distances. SMPTE has provided groundbreaking work in control systems also, with ESBUS technology allowing chaining of control panels, further simplifying wiring. A number of manufacturers implemented coax schemes with similar results. But, recently, several of the largest routing manufacturers have begun to deliver complex and intricate control schemes that communicate using TCP/IP communications over Ethernet.

By choosing a data-communications approach, video manufacturers materially changed the way routing systems are implemented. Most facilities already have LAN connections in place. Allowing the routing system either to live on the facility LAN or bridge to it provides interesting architectural choices. For instance, companies that have a potential need for wide-area connections can use their company WAN to extend routing control and monitoring, along with machine control, to distant locations without establishing additional circuits for special purposes. As remote-monitoring capability has increased, this approach has become much more desirable.

One result of this movement has been to greatly simplify the interfaces operators use to program routing switchers and read diagnostic information. Until personal computers became an integral part of broadcast systems, routing switchers were programmed from “command line” interfaces, usually using dumb terminals. As a result, the operator could not modify a routing switcher's operating parameters off-line and load the changes quickly. Instead, the process was tedious and time-consuming, and correcting errors was particularly unpleasant. By implementing advanced control schemes, routing manufacturers allow users to make off-line decisions. And, with some systems, users can store and load multiple setups as needed.

Systems have evolved to allow users to create the configuration in general-purpose software (for instance, spreadsheets), and later convert them, and sometimes compile them, into compact files and transmit them to the control system. Several routing products can now be both monitored and controlled using Web browsers. This raises the very powerful graphics capabilities of HTML to the top of the list of features. For instance, diagnostic screens can show the system in schematic form. The screen shows all control nodes and controlled matrices and other devices, complete with status information relevant to the system, as graphic information instead of text error messages that the user must interpret. By showing the interconnection as it is physically wired, the system becomes easier to understand, reducing time to repair.

The substantial scripting capability of HTML also allows manufacturers to design custom controls without designing controls that all users might not want. As long as the manufacturer supports direct control from a Web browser, you may be able to use the design scheme. (Some only allow programming, and others provide a toolkit for designing screens and controls.) By custom-designing PC-based control panels, you could, for instance, have single-button selections to reset the monitor wall in a control room for each production while retaining the ability to use common language for naming these for a single mouse click. If the routing system can provide status back on active crosspoints to the Web page, you can even get tally information for satellite records, perhaps even including machine status if the router also can provide machine control (as many routers can).

These features can extend to very sophisticated monitoring capability. Envision a centralized (or distributed) broadcasting system with Web-enabled routing and machine control over a company WAN. From the remote station, you could return low-bit-rate, thumbnail-sized video signals to the same Web page that is controlling the bypass switcher remotely. By using the remote router as a probe, you could troubleshoot an unmanned facility quite effectively, and even route around failed items from a Web page set up to look like a block diagram of the facility, swapping in redundant receivers, for instance. By using commercial solutions developed for other industries to provide new functionality and leverage the growth in networking, routing manufacturers have shown a level of innovation and attention to customer needs that has materially changed the face of our industry.

Cost vs. capability

In an analog router, it used to suffice for a manufacturer to provide a good control system and transparent video and audio paths. But digital routing systems have made other niche strategies necessary. For instance, some manufacturers concentrate on narrow markets, eschewing very large systems and instead design cost-effective smaller routers that can be used in niche applications, or connected in a web of small systems interconnected by trunks as necessary. This is an effective implementation strategy because the cost of routing increases roughly as the square of the number of I/O ports. Implementing four small 32×32 routers affords the same number of I/O ports as a single monolithic 128×128 matrix, though the latter has four times as many crosspoints.

Figure 1. As routing systems get larger, manufacturing economies of scale reduce cost per crosspoint.

Obviously, a routing system with the same number of I/O ports but four times the number of crosspoints will cost more. Logically, the cost of building one crosspoint should be vastly higher than building a large array. And, on a sliding scale, this is indeed true. The efficiency of manufacture is driven by packaging costs, power-supply cost, and intangibles like documentation and engineering costs. As Figure 1 shows, larger routers do provide a lower cost per crosspoint. Below 32×32, the trend does not repeat from manufacturer to manufacturer.

A score of signals

The range of signals that can be routed today is very important. The following list, though not exhaustive, shows the types of crosspoints and I/O channels that a manufacturer must consider supporting in a range of sizes:

  • SMPTE 259M (143/177/270/360Mb)
  • SMPTE 344M (540Mb)
  • SMPTE 292M (1.485Gb HDTV)
  • Analog NTSC/PAL (typically 10MHz bandwidth channels)
  • Analog audio (typically 20kHz channels)
  • Stereo analog audio
  • AES PCM audio (balanced 75V and unbalanced 110V implementations)
  • Timecode
  • RS-422 bi-directional ports
  • SMPTE 305M (DTV MPEG interconnect, 19- and 38Mb)
  • DVB ASI (270Mb NRZ MPEG interconnect)
  • Single- and multi-mode fiber

This represents a substantial product-line choice, and a manufacturer who supports all of the above has indeed created a flexible and worthy product line. Economics being what they are in our industry, we are increasingly asking for “more and less,” — that is, high-value features (like many signal types) at low cost. To the credit of the manufacturing community, it has responded to the challenge.

The core function of routing is to act as an electronic patch panel, connecting circuits on an ad hoc basis. A router is doing its best work when it is invisible to the user, who should only perceive the user interface. A router that is able to flexibly handle a range of signals will be “visible” less often and thus perceived as more important to an operation.

Router cooling and wiring must coexist.

Manufacturers have clearly understood this need and have developed wide-bandwidth routing solutions for video to partially accommodate this need. At the upper bounds of bandwidth is the SMPTE 292 HDTV interconnect (1.485Mb/s, 4:2:2 coded). Initially, HDTV routers were hugely expensive, with the first 32×32 routers costing upwards of $200,000. Today a router capable of HDTV rates and rates as low as 143Mb/s can cost as little as $16,500 (16×16). At the same time, the cost of larger routers with wide bandwidth has dropped significantly as the manufacturing volume has increased during the DTV/HDTV transition. One might logically expect that trend to continue, though the higher cost of designing and building high-bandwidth solutions will likely moderate that trend, slowing the drop in cost.

Analog vs. digital

Analog is far from dead in this market. It is indeed a difficult decision when doing conceptual planning for a facility to decide if an all-digital plant is right. It is always possible, but it may not be appropriate when the facility must support a broad variety of signal types. Almost all video facilities have some analog requirement, if for nothing else than analog monitoring circuits. Since most source devices have both analog and digital interfaces, it is often convenient to implement a small analog “layer” to avoid growing the size of the digital matrix. If this can be controlled in a seamless control system, it will become an invisible distinction for operators.

It is not at all unusual for a broadcaster to choose to implement a fully digital video plant, but to use mostly, or all, analog audio. This subject is beyond the scope of this article. But we can say that the choice is often driven solely by economics. No one would dispute that you can build a higher-quality plant with AES signals than analog signals. But you must decide if the additional quality is worth the potential additional expense of upgrading the rest of the audio system. Converting marginal audio signals to AES will not improve the sound in a facility, but it will have an impact on finances.

Additionally, one might consider embedded audio for the same reasons, perhaps resulting in more complex answers due to the technical complexity of a production facility where synchronization between audio and video is affected each time audio mux or demux operations are performed. Eliminating the audio levels of a matrix, however, may well swamp any cost disadvantage. It is a calculation worth doing with more than one manufacturer's hardware.

There are defining differences between manufacturers' digital (and analog) routers. You must consider factors such as cost, size, power consumption, redundancy in power and signal electronics, control architecture, control-panel design, ease of programming, maintenance cost and ease, and technical specifications.

Crosspoint implementations

All manufacturers offer redundant control systems and redundant power supplies. One even offers redundant crosspoints in a strategy where two crosspoint cards are required to keep all signals flowing, but a third is installed and capable of taking over the work of a dead cousin.

Echostar’s Cheyenne, WY, facility employs a large-scale routing system.

This allows you to make repairs without ever taking the router out of service when even a single crosspoint in a large system has failed. This kind of advanced thinking is not affordable in small systems, but is well worth having in a facility that must be online around the clock with no excuses.

Routing switcher designers and manufacturers are slowly moving to TDM technology for crosspoints. Though such a crosspoint system uses potentially fewer cards and less point- to-point wiring, failures could be harder to troubleshoot and repair quickly. One manufacturer designed an audio routing system using asynchronous transfer mode (ATM) data technology. Several manufacturers sell audio switchers that allow you to split and combine the audio channels in an AES pair freely between all pairs and outputs. Another offers a single-frame solution in which half of the crosspoints can be digital and half analog, yet all signals are available in both domains. Others allow you to connect matrices (audio, at least) over high-speed TDM links that can make a very large audio system distributed over a large area in a plant look like one monolithic frame with access to a potentially huge number of I/O channels.

What's next?

Though no prediction of the future is possible with assurance that it really will evolve in a particular direction, it seems clear that the convergence of data-communications techniques and discrete audio and video routing systems will continue. As our signals move increasingly towards compressed signals where the essence is simply data, it is hard not to see such a movement being a logical extension of the injection of data techniques in the signal path. Video devices are emerging with Ethernet connections as common ports, and other data connections cannot be far behind. Most devices have both inputs and outputs, so bi-directional data circuits with sufficient bandwidth, isochronous throughput and frame-accurate switching almost certainly will begin to nibble at the edge of the traditional video-routing business.

John Luff is senior vice president of business development at AZCAR. To reach him, visit

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