Streaming to Mobile Devices

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Trends in Technology, April 2010

Putting it all together, end to end

Let's take a look now at how a connection is made end-to-end when an end-user clicks on your application.

For starters, part of what the application developer does is to code the unique URL you want to use for a particular stream. Obviously a different URL can be used on the basis of the platform type.

After this URL is resolved, a redirect server is reached. In addition to redirecting you to the yet another URL, this server likely takes note of the fact that you requested the service. (You've just become a statistic.) This second URL points you to the CDN.

At the CDN, your request reaches a DNS that does a few things:

  • Reads the source of IP address of the requester
  • Does a lookup of the owner of that IP address
  • From that owner information, a reckoning is made of the location of the requester
  • The DNS then decides which of its POPs is the best place to serve your content based on: The closest physical proximity; network congestion encountered reaching that POP; server usage at that POP; and load sharing.

    Once the CDN's DNS comes up with an answer, it resolves the requested URL into an IP address for the user to attach to. The last mile connection is now made -- via unicast. In the case of mobile devices, the physical layer is done via two radio links: one from the cell site to you, and of course the other from you back to the cell site.

    The number of of smart phone users keeps increasing, and there's no end in sight. I for one don't believe streaming will ever supplant broadcast radio, but it is abundantly clear that streaming is growing in importance in our business. If you haven't already availed yourself to the new crop of Internet listeners, now is really the time. It's still early in the game, and definitely not too late to get in.


  • AirKast
  • Akamai
  • AudioTX
  • CDNetworks
  • Limelight
  • Orban

    Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at

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