Why Asymmetric Bandwidth is Important to IP Video Systems

By John Honovich, Published Jun 07, 2008, 09:52pm EDT

You may notice that your home cable modem offers greater bandwidth going down to your house than going up to the Internet. For instance, while you may have 3 Mb/s download, you can only upload at 384 Kb/s. This is an example of asymmetric bandwidth, a very common and important factor in designing IP Video systems.

Generally, as a home user, this works out fine. Normally, what you want to do is access resources or view materials from remote servers (newspaper websites, iTunes, etc.). The average user rarely needs to upload lots of data/files/video quickly.

This is the opposite when designing IP video systems. With IP video systems, you want to deploy a number of cameras at your remote facilities, stores, branch offices, etc. And usually, you are interested in watching or recording those cameras at your central facility or other facilities. In this case, you are 'serving' video from your remote facility to your main facilities. This is, of course, the opposite of what you usually do, which is receive data/files/video from a main office/server.

As such, you have double design issues. First, bandwidth available to your remote sites is low (usually 5 Mb/s or lower max downstream). Second, upstream bandwidth (the bandwidth you need to serve your IP video) is only a fraction of what the already meager downstream bandwidth is.

And there's no solution to 'asymmetric bandwidth' on the horizon. This is not a minor technical issue. This is a fundamental electrical engineering issue of building shared networks like cable modems and DSL. You can eliminate the asymmetry by buying T1s or DS3s or fiber to the home but you are going to pay a massive premium for these alternative. So while they are technically feasible alternatives, most businesses do not find financial justification for leasing these services for purposes of IP video systems.

The solution used, almost universally, is local recording of the IP cameras at the remote site. This is what DVRs have done for years and you can expect the same for NVRs for years to come as well.

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