Routing systems
Nov 1, 2008 12:00 PM, By Phil Cianci
Distributed routing and media networks will change the way content is moved within a facility.
Figure 4A. Distributed routing with high bandwidth “uplink” capabilities
Select image to enlarge.
File-based routing
As acquisition and production move away from tape-based workflows, there is an opportunity to distribute compressed content in file format. Many cameras now support file-based acquisition; play to air is increasingly from media servers. As content is repurposed over the Web and included in DTV multicasts, it may never exist as baseband audio and video.
Figure 5 illustrates an integrated traditional and IT routing system. Ingest and playout servers are already connected to the media network. The key additions are codecs with network interfaces that are IP-compatible. Content may be transferred from source to destination over the media network. Centralized storage is accessible from the network, and content can be routed there as well.
Naturally, there are issues to resolve. Content consists of essence and metadata. The essence/metadata association must be managed during content movement. There can be problems with real-time delivery of content to servers. Network congestion must be avoided by verifying bandwidth with rigorous testing, and efficient routing protocols that guarantee Quality of Service are necessary. Compression, decompression and transcoding will add processing delays and affect lip sync.
Configuration and control
Distributed routing and the inclusion of the media network will make system configuration and control significantly more of a challenge. In a centralized routing topology, an input is sent directly to an output — a straightforward source A to destination B switch. In a distributed scenario, point A to B may make a number of “hops” from router to router over a switched connection.
Optical TDM routing is complicated. Each switching node in a distributed architecture must demultiplex, then switch the signal of interest to a time slice that has as its destination the desired output port. This may entail a number of hops, each requiring a demux, switch and remux. This makes SDI routing more and more like IP packet routing. However, using TDM, packet jitter is non-existent, but latency increases with each hop.
Figure 4B. Distributed routing with high-bandwidth “uplink” capabilities and baseband routing ring
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Design-friendly configuration applications will be the only effective way to configure a distributed routing system. There will be the need to view systems as physical sources and destinations managed by logical “level” assignments across distributed resources. This will require careful planning and an understanding of workflows.
IP addressing schemes for devices and control panels must be carefully planned so that they do not conflict with existing network addresses and so that there are sufficient addresses reserved for future expansion. Suffice it to say that static IP addresses will be necessary.
Ready for prime time?
Although not presently available on the broadcast equipment market, there have been discussions, white papers and R&D efforts to develop BE/IT hybrid router systems. However, distribution and routing of uncompressed signals will not disappear anywhere in the near future. There is also a lot of legacy analog audio and video material to keep in mind.
Switched GigE has enabled distribution of compressed content to workstations and servers. However, 1Gig is limited. At best, four streams of content at 200Mb/s can be simultaneously transferred, provisioning 20 percent header routing, control and file validation information.
If 10GigE paths are switched to servers and workstations, more than one uncompressed 1.5Gb/s HD stream could be supported. 100Gb/s is close to standardization and commercial deployment and may support 50 1.5Gb/s streams.
Figure 5. A BE/IT routing topology
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With 10GigE paths to devices on a 100GigE network, the integration of SDI and IP routing in broadcast facilities becomes attainable. The limitations of dedicated ports to distributed routing nodes can be resolved with 100Gb/s single-cable interconnects. It is not all that far-fetched; 40Gb/s Infiniband and OC 768 exist now.
It is time to plan ahead for the inevitable, all file-based production work-flow. The routing of compressed content should be considered as part of the overall facility routing system.
Phil Cianci is a design engineer for Communications Engineering, Inc.
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