A Buyer's Guide to Cellular Multiplexers 2014
A typical channel-bonding link aggregator does not have this layer of communication. It assumes a fixed QoS across the various aggregated links.
Cellmux integrates the video encoding, the channel bonding, and the link aggregation and so that both the field equipment and the remote demultiplexer are able to communicate with the video encoding process and vary the bitrates and handle different network conditions in a smooth and integrated way. This ensures that the demultiplexer can then forward the best stream possible to the origin server of the distribution network even if the network conditions are constantly and rapidly varying.
Get the Right Equipment for Your Needs
If you are trying to bond several fixed ADSL links in a fixed location for web traffic, then you only need a link aggregator. If you are in a fixed location or bonding two networks with QoS guarantees and aiming to stream video, then you can probably use a channel-bonding link aggregator, which will be considerably cheaper than a cellmux. However, if you want to use multiple networks with no QoS guarantee to stream the best video possible then you will need a proper cellmux. The rest of this article assumes you’ve determined you need one.
Make Sure the Source Will Work With Your Workflow
The next thing you need to consider is your workflow. Most demultiplexers will offer two types of output: They will provide a mechanical SDI or HD-SDI interface that will produce the live video stream. They will also offer the same video on internet protocol (IP) via an Ethernet interface, and this will typically produce H.264 encoded video encapsulated in an MPEG-TS transport on IP.
Some of the devices will allow direct contribution to Wowza Media Server or Flash Media Server. Alternatively, some may only offer streaming outputs, and this may compromise your ability to use the resulting output in your broadcast workflow.
Most of the devices also will allow a file-based transfer, so while this “store and forward” feature is not about streaming live (so the telecoms and links quality may be less critical), you’ll want to check on the compatibility of the output files with the rest of your workflow. A proprietary implementation of MPEG-TS may demand a transcode or some other treatment of your archives, and this may negate all the effort of implementing a fast backhaul using cellmux: There is little point getting the video back to base in a matter of moments only to have to wait an hour before your transcoding system is available to actually prepare the content for broadcast.
Plan Your Usage
Plan your usage. While obviously cellmux offers versatility in terms of location and access if you are always broadcasting from the same location and (for example) have clear view of the sky, you may find a satellite-IP-based system is going to cost the same, and it comes with a QoS service-level agreement that no cellmux can offer.
If, however, you are planning to broadcast from a moving vehicle in a dense urban area, then without a doubt cellmux will find cellular signals and even the compact units with small antenna will be able to find sufficient capacity to deliver your source signal back to base.
Where it becomes more complex is in the marginal areas where there may only be a limited amount of cellular capacity. In that context, using a cellmux with a flexible, high gain (perhaps roof-mountable) antenna will make all the difference, where a compact unit would struggle.
Ask an Expert
Talk to me! I have had the privilege of playing with may of these devices (you can see an increasing list of benchmarks published in Streaming Media). It has been tricky getting access to all the products and, even with my press hat on, the logistics of getting hands-on with equipment from vendors that are based all over the world is complex. It is highly unlikely you will be able to play with all the products you would like to before you make your final buying decision, but if you have any nagging doubts or considerations, do feel free to ask me.
In the spring, I am launching a microsite (cellmux.com), which aims to bring all the data into one place -- my editorial reviews will remain published in Streaming Media, but the raw data, community information, and press releases from the vendors will be collected on cellmux.com, and I hope this will augment the editorial content in these pages to help you make informed decisions. That said, please do reach out and ask me directly. I always enjoy hearing about workflows and their challenges -- particularly challenging live ones!
This article appears in the 2014 Streaming Media Sourcebook.
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