Bit Flipping at work

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At work I deal with a variety of problems, and I currently have a long running issue that is kind of interesting.

The short version is that we have a subtle network problem with network connection between two buildings. This problem affects about 0.14% of the traffic that goes over the fibre optic link between those two buildings. We've got about about 20 buildings with network in them. This problem only shows up between two specific buildings.

The long version is quite interesting, but to understand it you need to know two things about how networks work.
  •  The idea of packets
  •  that information is sent as bits
Just like everyone else, at work we use an IP datagram network. Information is sent from your computer as packets of information, and is received as packets. If you load up the company web page, you might send about 110 packets requesting the page, and receive about 176 packets.

When those packets are sent over fibre optic links they are represented as bits, a sequence of '0' and '1' symbols. So if you were watching those symbols fly by you might see '110110011111100001101'. The computers and network switches know what all these 1's and 0's mean, and you get to see a web page.

Now, the problem! After noticing some small irregularities, and doing a great deal of investigation, I noticed that about 0.14% of the time a 1011 sequence of bits is changed to 1111. For some reason we don't understand, one of these bits gets flipped.  I don't know why. Just another problem to solve.

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This page contains a single entry by Geoff Crompton published on May 12, 2010 7:22 PM.

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