What went wrong: end-to-end ATM

Red Pineapple was kind enough to share his 15-year-old ATM slides. They include interesting claims like:

ATM has the potential to displace all existing internetworking technologies
One single network handles all traffic types: Bursty data and Time-sensitive continuous traffic (voice/video).

All these claims are still true if you just replace »ATM« with »IP«. So what went wrong with ATM (and why did the underdog IP win)? I can see the following major issues:

  • ATM is a layer-2 technology that wanted to replace all other layer-2 technologies. Sometimes it made sense (ADSL), sometimes not so much (LAN … not to mention LANE). IP is a layer-3 technology that embraced all layer-2 technologies and unified them into a single network.
  • ATM is an end-to-end circuit-oriented technology, which made perfect sense in a world where a single session (voice call, terminal session to mainframes) lasted for minutes or hours and therefore the cost of session setup became negligible. In a Web 2.0 world where each host opens tens of sessions per minute to servers all across the globe, the session setup costs would be prohibitive.
  • Because of its circuit-oriented nature, ATM causes per-session overhead in each node in the network. Core IP routers don’t have to keep the session state as they forward individual IP datagrams independently. IP is thus inherently more scalable than ATM.

The shift that really made ATM obsolete was the changing data networking landscape: voice and long-lived low-bandwidth data sessions which dominated the world at the time when ATM was designed were dwarfed by the short-lived bursty high-bandwidth web requests. ATM was (in the end) a perfect solution to the wrong problem.

3 comments:

  1. I remember how much troubles I had trying to understand ATM back in 1993 - I was 14 years old then and that stuff kind of blew my mind away ;)

    ATM to the desktop topic was circulatiing all around 90s - I wonder if anyone was imaging then this emerging into MPLS and killing ATM itself.

    And do we hear anything about MPLS to the desktop nowadays? :)

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  2. There is no need for MPLS to the desktop. MPLS is a core technology (effectively adding virtual circuits to IP infrastructure) and there's nothing to gain (and scalability to lose) by extending it further.

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  3. I think you have missed the major issue, which is the cost. LANE was ugly but there was no need for it in an end-to-end ATM world.
    I believe that ATM came too early with very large costs that could be handled by TELCOs only, and not by the average ISP, home user, small corporates.
    So, we are now doing some kind of workarounds using MPLS, per-hop QoS, trying to figure out how each platform implements QoS etc.

    ReplyDelete

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Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.