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October 17, 2007

Broadband Primer Part 2

Yesterday’s post explained broadband (sort of), bandwidth, speed, kilobits, megabits, the difference between bits and bytes and some of the many reasons why your Internet experience is almost never at the speed advertised by your Internet Service Provider (ISP). Today’s post, class, is about why downlink (to you) and uplink (from you) speeds are often different and why you might care.

Most American’s didn’t get on the Internet until the WorldWideWeb made online information easily accessible and appealing. When you request a page from a website, you send a simple line of text on the uplink (like http://blog.tomevslin.com which is 27 bytes long counting the carriage return you don’t see) and you usually get back lots of pictures and text; over a quarter of a million bytes of text is returned by this simple page request for my blog and the embedded pictures probably bring the whole page size up to over two million bytes. So 27 bytes up, two million bytes down.

If you were designing a road where most of the traffic went in one direction, you’d put more lanes in that direction than in the other. The “pipes” that link you to the Internet can be partitioned to separate the bandwidth devoted to downlink and uplink. Given the huge imbalance during web browsing, it made a lot of sense for consumer Internet access to be designed with more capacity – often most of the capacity – devoted to downlink. This is called asymmetric use of bandwidth.

This asymmetry persists today, Basic DSL, for example, usually has an downlink speed of 768 kbps (kilobits per second if you skipped yesterday’s lesson) and an uplink speed of 128kbps. Most cable plans offer two or three times as much downlink capacity as uplink.

But we are changing the way we use the Internet. When we send email, the downlink usage and the uplink usage are almost the same (not quite because one upload can reach multiple recipients and because of spam). Our emails are getting much, much bigger. When we work at home, we often have a need to send huge emails including PowerPoint presentations, architectural drawing etc. If we have kids, we’ve got to email their pictures to grandma – and the videos we now send are even bigger.

Increasingly WE supply the content we care about on the Web. WE upload the videos to YouTube. WE “share” music. WE populate Flickr with pictures. WE post the blogs and the comments on the blogs. Some of us have web cams sending new pages up very frequently. All of this adding content requires uplink capacity.

When we use online backup (turned out to be a lifesaver for us), we upload millions of bytes every night and download almost nothing unless and until we have a catastrophe.

If we make Voice Over IP (VoIP) calls or video call, we use as much uplink bandwidth as downlink.

Michael Birnbaum, who runs the Vermont WISP (Wireless ISP) Cloud Alliance, comments:

“Most users upload rarely in relation to their downloads. This is changing, though. As more and more users upload their videos to YouTube, for example, upstream needs will increase. We try to deliver the most usable product the economics dictate. Right now, we offer twice as much downstream speed as up. This leaves less purchased speed fallow from the subscriber's point of view. As the demands change, we will adjust.”

He adds that they can give business customers who need it symmetrical access today. (We’ll be hearing more from Michael’s comment in a later post).

Many ISPs are not as forthcoming as Michael about their uplink speeds and just feature the faster downlink speed. But, if you are anything but a very passive viewer of pages, you want to make sure that your ISP (should you be lucky enough to have a choice) offers you substantial uplink as well as downlink speed.

More on uplink and downlink speeds here.

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