Paul Greene and Don Morgan /
09.01.2008 12:00 PM
NVISION's NV8576
The large-matrix, multiformat router ensures signal integrity.

The need for large-matrix routers is driven by the increased availability of video distribution channels to meet consumer demand for a richer offering of video services. This in turn increases programming volume as well as playout capacity. Another factor is the gamut of audio and video formats: SD-SDI, HD-SDI, DVB-ASI 3Gb/s and synchronous or asynchronous AES audio.

Until now, a router size of 512 × 576 was sufficient, but today, routers need to scale up to 1152 × 1152 for many applications. The router must also ensure signal integrity, full redundancy protection and power management to guarantee uninterrupted, on-air operation. The NVISION NV8576 large-matrix digital multiformat router addresses these requirements.

Frame size and linear expansion

The NV8576 router design is efficient in both vertical rack space and depth, two critical factors for installation planning. The frame supports 576 × 1152 in a single 32RU. At 16in deep, there is space to install the 1728 cable capacity of the router in a conventional 30in to 36in deep rack.

Traditionally, doubling a given matrix size requires four frames with external input DAs and secondary switches. With NVISION's linear expansion of large HD video routers, all input DAs and secondary switches are internal, eliminating the need for extra cabling and rack space. A 1152 × 1152 router is created using two 32RU frames, each configured 576 × 576, interconnected with high-speed differential expansion cables.

The active internal DAs and secondary switches provide high-quality signal integrity and stability in the router, including 3Gb/s data rates. Passive splitters and combiners could be considered, but can create termination problems. For example, if a connector is removed for any reason, the impedance for the other output is compromised.

Multiformat capability

The router can be configured as video-only, audio-only or a mixture of the two in one frame. Signal formats include SD-SDI, HD-SDI, DVB-ASI 3Gb/s and synchronous or asynchronous AES audio. Fiber I/O connectivity is supported for long-haul applications, such as tie lines between trucks or studio links in large facilities.

Impact block and redundancy

Large-matrix routers can create big impact blocks if not designed correctly. In the NV8576, inputs are in groups of nine, and outputs are in groups of 18. This design results in small router I/O cards that improve signal performance and are mechanically stable. While I/O can be managed in small blocks, large router crosspoint cards can represent a significant failure point. This challenge is remedied by a full N+1 redundant crosspoint option. In the event of the complete removal of a crosspoint card (288 × 288), a spare card capable of completely replacing the removed card can be activated in a single vertical interval. Thus, the largest impact block in the system is a single input or output card.

Most routers today use a square matrix architecture that is framed for equal numbers of inputs and outputs, such as 288 × 288. Square routers work well for routine applications but are limited for other applications such as large monitor walls. Typically, this implementation burns valuable router output space. (See Figure 1A.)

An alternative design is the rectangular matrix with larger output capacity than input capacity, as in the NV8576 router. Figure 1B shows a rectangular router with twice as many outputs as inputs, while occupying the identical rack space as the square matrix. This design supports additional output applications without burning core router output space.

Signal integrity and connector density

Signal path length is critical to the transmission of high-speed digital signals. With 3Gb/s signals, the dielectric absorption of the Flame Retardant 4 (FR-4) printed circuit board (PCB) material renders the signal unrecoverable within short trace lengths. Internal signal path length must be as short as possible to ensure the best signal integrity. (See Figure 2.)

Also, the proven use of DIN 1.0/2.3 connectors on large routers provides connector densities two to three times that of conventional BNCs. These connectors enable the use of shorter traces in the NV8576 matrix design, along with major rack-space savings.

Power and cooling

Power levels inside the routing frame should remain low so that a catastrophic short-circuit event cannot occur (arc welder effect). Multiple branches of DC power from the power supplies ensure that no single branch carries more than 170W or 3.5 amps within the router frame.

The cooling system consists of front-removable fan trays located in the top and bottom of the frame. Air is ingested through a vent in the center front of the frame, and the exhaust comes from the top and bottom rear. An additional rear cooling duct supports fiber I/O options. The fans have temperature speed control and use a magnetic-bearing squirrel-cage design.

Conclusion

As in the NV8576 router, the linear expansion of a large-matrix multiformat router gives broadcasters the largest number of inputs and outputs (1152 × 1152 at 3Gb/s) for today's and future broadcasting requirements, and within only two 32RU frames. The router architecture ensures signal integrity, full redundancy protection, power management to avoid catastrophic equipment failure, and there's no reliance on external distribution. Expansion from one frame to two frames in the field enables an uninterrupted, on-air, upgrade path that is unique to this router design.


Paul Greene is product manager, routers, and Don Morgan is senior systems engineer for NVISION.



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