AMP VISUAL TV built its Millenium Signature 12 HD/4K-capable, 40 camera OB van on a Riedel MediorNet 10 Gb/s fiber network. Image Riedel.
A few years ago, on a visit to the CBS Broadcast Center in New York City, a visitor and host were walking a hallway that seemed longer than a crosstown Manhattan block. Both sides of the hallway sported heavy cable races hung from the ceiling, each with a cross section of a foot square, brimming with cables.
“How many of those cables aren’t being used?” the visitor asked.
“Nobody knows,” was the quick answer.
CBS has broadcast from West 57th Street since at least 1963. One can imagine the inventory of unused cables buried in those trays included once-important paths for monochrome TV, composite NTSC, RGB and component color and other almost-forgotten signal formats.
In the future if not today, broadcast plants will need to support video formats beyond 1080i, perhaps even beyond UHD-1 (4K) and UHD-2 (8K), possibly with a mixture of bit depths, uncompressed and compressed streams, all simultaneously. By moving beyond some old notions and planning for the future, all this and more can be accommodated in smaller footprints than used in today’s broadcast plants.
This article is the first of two intended to help broadcasters plan for future needs while avoiding the obvious pitfalls, unintentional or otherwise, created by proponents and evangelists of particular approaches to the future.
Figure 1. Comparing the bandwidth of fiber against other types of connecting cable is no contest. Fiber wins in virtually every category.
At the outset, we need to be clear the further out our planning horizon, the fuzzier the horizon line appears. Even with the clearest of foresight, by the time an anticipated requirement arrives, the shape and extent of the need might have morphed.
A case in point is the International Telecommunications Union (ITU) development of the BT.601 standard (also known as CCIR 601) to bring the world’s analog TV stations into digital broadcasting with minimum pain. The offered “gold standard” for hybrid analog and digital broadcast plants caused most of the adopters to end up burnt and isolated when SMPTE SDI protocols (and audio/metadata embedding into video) eliminated the problems created by BT.601 implementations. The degrees of freedom created by the “internationalized” BT.601 work caused more problems than were solved and delayed widespread adoption of the superior SDI approach.
That said, we can anticipate that future broadcast plants will need to accommodate “deterministic” video forms such as the SDI family of protocols, as well as forms based on transport of IP packets and significant increases in bandwidth requirements per video stream.
Basic requirements in future-proofing a broadcast plant:
- Support current topologies and technologies while providing for incremental and “full-cut-over” approaches to any future standard or standards that emerge;
- In-service enhancements to broadcast plants need to be implemented without taking existing plants out of service or degrading any programming service;
- Costs in future-proofing must be comparable to current approaches and the benefits and flexibility must be clear even if they are to be realized over the long-term;
- Broadcasting plants of the future must be designed to be as, or more, reliable and more flexible than current plants;
Before we go further, let us iron out a few kinks.
Engineering fetishes are curable
Engineering fetishes do not usually involve leather, rubber, latex, Speedos nor stilettos. Engineering kinks often have more power than do those. These types of fetishes are defined by Oxford Online as:
- an excessive and irrational devotion or commitment to a particular thing;
- an intimate object worshipped for its supposed magical powers or because it is considered to be inhabited by a spirit.
Coax and BNC connectors have no magical properties and are superior for carrying up to 4Gb/sec. data flows. However, the future is likely to involve carrying 6Gb/sec, 12Gb/sec, 24Gb/sec. and higher bit rates for video and associated audio, data essence and metadata streams.
At NAB several years ago, a prototype NHK 8K video camera sported 48 separate BNC connectors for video alone. Imagine routing 48 coax runs in a broadcast plant while keeping the output in phase! The following year, NHK showed a prototype 8K camera the size of two balled fists and sporting a single fiber optic connector in place of 48 BNCs.
Table 1. This table compares key performance criteria of CAT-7, RG-6U and Single Mode Fiber. For many video applications fiber becomes a highly desirable choice because it excels in most comparisons with other solutions.
Ethernet NICs include clock circuits that cannot be updated, nor can RJ-45 connectors and CAT-7 cabling carry 10Gb/sec. a usable distance. Uncompressed 4K video requires at least 12 Gb/sec. 100Gb/sec. copper cabling is limited to runs of 15 meters or less. A comparison of RG-6U coax, CAT-7 and single-mode fiber characteristics is diagramed above this article and are listed in Table 1.
The cure for the BNC, RJ-45 and copper fetishes is single-mode optical fiber. Electrical and optical connectors on Small Form Pluggable Plus (SFP+) interface devices assist in bridging the copper world with the fiber future. SFP+ dongles slip into the SFP+ slot on a device or hang out the back end.
SFPs interface devices offer SDI and HD-SDI connectivity via BNC, Ethernet via RJ-45 and fiber connectors. SFP+ connectors are limited to 10 Gb/sec, but physically compatible Quad SFP+ bulkhead connectors and interface devices provide for up to 40Gb/sec. throughput. Once copper is in the rearview mirror, newer fiber-only pluggable connectors will easily handle 100 Gb/sec. and more.
A strand of single-mode fiber optic cabling provides at least 700 Gb/sec. throughput. The next article in this series will detail employing fiber optic connectivity in and between broadcast plants. Going forward, devotion to copper, BNC and electrical connectivity will be a limited, expensive, and bulky fetish.
Using Precision Time Protocol (PTP) for sync
Despite the importance of highly accurate timing signals to video continuity, sync, timing and time are usually disjointed within television plants. Video sync generators require dedicated wiring to distribute those signals and are incapable of providing time of day. SMPTE ST-12M time code can carry time of day in separate dedicated wiring, although it often does not due to incompatibilities and seldom is ST-12 time of day available throughout a plant.
Both video sync and ST-12 are bound to video frame or source video format, making synchronous intermixture difficult. Network Time Protocol (NTP) via IP networking does distribute time of day but is not particularly useful in media flows.
There is a screaming need for a unified, IP-based approach to distributing high-precision time of day signals that can be consumed directly or indirectly by all systems within a broadcast plant. Such a system would necessarily need to be independent of any video or audio format and upstream of sync and time code generators.
Employing a “grandmaster” IEEE-1588:2008 (v2) Precision Time Protocol (PTP) sync generator is the embodiment of the best case unified approach to sync, timing and time of day. IEEE-1588v2 is supported by SMPTE ST-2059 and Audio Engineering Society AES-67 standards.
PTP signals, like the NTP signals they resemble, are distributed as IP packets or directly in Ethernet frames. PTP provides a time of day reference with precision on the order of 1 ns and accuracy of between 10 and 100 ns, better than that needed for television sync. An embodiment of PTP in a television plant is shown in Figure 2.
Basically, a “grandmaster” PTP timing reference employs an internal or external high-precision time reference to create PTP datagrams which are distributed via IP networking to media-centric sync generators, media devices, local "slave" PTP generators and even desktop computers.
Each of the devices that consume PTP continually interact with the grandmaster or master PTP generators to measure dynamically network latency and create a localized time of day reference. Many vendors of media sync generators already offer PTP coordination as a standard or optional feature.
PTP time is supported by a wide variety of COTS devices, including computers and network switches. The key is whether the NIC or NICs create the essential “hardware timestamps” which are compared to PTP time from the reference as adjusted for network latency. Even inexpensive, newer computers include PTP hardware timestamp capability.
Ultimately, as PTP trickles down to more media devices, traditional media-centric sync, including black burst, tri-level, 1 PPS and SMPTE-S12 can be minimized or eliminated. Thus, PTPv2 works as advertised today and is the way forward for broadcast plants.
How to proceed
- Buy just a little bit more than you need today – Contemplate replacement equipment that supports higher standardized frame rates and “screen sizes” than you need today. Be looking beyond the “usual suspects:” often there is new gear with such support at the same or less price than the usual suspects offer today. Even where this is not the case, buying just a bit more than you need will give your equipment a longer service life and lower overall costs than gear ‘sufficient” for current needs.
- Uncompressed video over IP = Single-Mode Fiber optic cabling
- Buy HD equipment now that can be upgraded later via software – SMPTE has adopted standards to address 1080p, 4K and 8K within and between broadcast plants. The makers of interface circuits have baked these standards into chips sold to equipment vendors. In many cases, moving to higher standards might mean activating a license key and possibly adding storage capacity.
- Automatic detection and configuration of inputs – All equipment needs to detect the standardized media format (SD, HD, 1080p, 4K, etc.) on inputs and automatically configure and adapt without any human intervention. Outputs must be configurable to support any currently-standardized media format.
- Don’t bind processing equipment to emission formats – To get the most out of 1080i29.97 (as an example), performing processing at 1080p59.94 (or higher) will improve output quality visibly and audibly while easing transition to higher-quality emission outputs. Your mantra should be “over-sample in temporal, spatial and bit-depth domains and down-convert at the last possible point in the workflow.” By doing so now, your plant will be ready for higher quality emission formats of the future.
- When replacing copper wiring with fiber optics – Provision multiple strands within the same jacket to bake in flexibility and redundancy.
For many reasons, broadcasters need to buy today with an eye to the future. Try to plan in ways that the technology needed today can be repurposed or upgraded as needs change. Few of us will have the opportunity to build an entirely green field site. Even so, we can build new technology islands, implement software solutions, and use fiber when possible.
Careful planning will reduce bottom line CAPEX by allowing solutions purchased today to meet the needs of tomorrow.
John Willkie is a former broadcast engineer, systems integrator and now consultant based in San Diego, CA.
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