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Transcript:
Building Unreliable Systems out of Reliable Components:
The Real-Time Story
Slide 3
Building Unreliable Systems out of Reliable Components:
The Real-Time Story
Slide 3 – Electronics Technology Delivers Timeliness The basic story is that electronics technology delivers timeliness, in fact, with incredibly good precision. We’re routinely able to construct synchronous digital logic that maintains synchronizations sub-nanosecond across distributed systems for reasonably small scales and a little more course granularity – maybe 10’s of nanoseconds over courses of 100’s of meters - and yet the overlaying abstractions of software throw all of this away. In fact, it just tosses it right out the window. I think it is very telling. We have been working with a group at Agilent that’s working on time synchronization techniques based on Ethernet. So one of the things they’re working with is an IEEE standard that they sort of instantiated called IEEE 1588, that over reasonable standard Ethernet hardware, can get time synchronization on the order of 10 nanoseconds, or so, across the scale of a factory floor. There was recently a meeting in Geneva. There was a bunch of participants in the standardization process there who brought prototypes so they could check out whether the standard was working by getting these things to interplay, all but one of the prototypes was a hardware implementation. The hardware prototypes were all able to achieve timing synchronizations between 5 and 40 nanoseconds of timing synchronization across a distributed system. The one software implementation was able to achieve approximately a millisecond of synchronization. That’s five orders of magnitude – ok. The underlying technology is the same – ok, but somewhere in the design process they have thrown away 5 orders of magnitude in timing precision. OK, how does that happen? References: IEEE 1588TM-2002 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems http://ieee1588.nist.gov/ Agilent Technologies ships LXI IEEE-1588 demonstration kits to members of LXI Consortium http://www.agilent.com/about/newsroom/presrel/2005/29aug-al05002.html
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