What is Broadband?

13 October 2005

How much bandwidth is required to stream a high definition movie that is two hours long to a home receiver that will play that movie on a 52 inch display?

Same question, but instead of streaming that movie, we want to download it in a minute.

The point is that our current notion of a domestic Wi-Fi cloud probably won’t meet many of the needs that we have. I remember 10Mbps Ethernet. I use 100Mbps Ethernet today, but my Wi-Fi throttles that to around 11Mbps or less.

Something tells me that really high definition video is going to require us to move 6 or 8 GB of data in a hurry.

Calculations if you have them, please!

* * * UPDATE * * * Okay, here goes.

First, let’s clear up the confusion that arises when telecommunication types talk to computer engineering types. For the purposes of this discussion and mathematical simplicity, we’re using the following (slightly inaccurate) conventions:

  • 1 byte = 8 bits
  • 1 gigabyte = 1×109 bytes = 8×109 bits
  • 1 Gbps = 1×109 bits per second

Also, in light of the Blu-ray disc, we’re going to use 50GB as the capacity of a dual layer disc that holds 8 hours of high definition video with audio. In other words, that disc will hold approximately four movies. So, a two-hour high definition movie represents roughly 12.5 GB of data (or 100×109 bits).

To move that much data over the wires (or air?) and save it in a minute, we need a system with a throughput of 1.67Gbps. Contrast that with a cable modem speed of even 3Mbps, and you see that we need something that is over 550 times as fast as what is generally considered fast today.

An optical fiber in the telecommunications world that carries that much data that fast is called an OC-48. It will carry 2.488 Gbps. That’s the long-haul need. In the last mile and the local area network, you need that same 1.67Gbps. That means we’re looking at something beyond 10GigE to insure the kind of throughput required.

There aren’t many telecommunications carriers that can meet that requirement, much less ISP’s, regional phone companies or WiFi hotspots. Yet, does anyone doubt that we’d like to be able to move a DVD worth of information from place to place in a minute or less? Does anyone doubt that we want to do that from a laptop situated anywhere in the USA?

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