

Ask HN: Inherent limitation of networks? - alanh

Isn’t there a mathematically proven limitation of networks, in that you can never be 100% sure that two clients are on the the same page?&#60;p&#62;I could send you a message, and to be sure you got it, I could ask for a confirmation. But are you sure I got the confirmation? We can confirm the confirmation, but then it’s confirmations “all the way down”, isn’t it?&#60;p&#62;What’s the name for this paradox?
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alextgordon
Perhaps you're thinking of the Two Generals Problem?

    
    
        Two armies, each led by a general, are preparing to attack a fortified city.
        The armies are encamped near the city, each on its own hill. A valley
        separates the two hills, and the only way for the two generals to communicate
        is by sending messengers through the valley. Unfortunately, the valley is
        occupied by the city's defenders and there's a chance that any given messenger
        sent through the valley will be captured. Note that while the two generals
        have agreed that they will attack, they haven't agreed upon a time for attack
        before taking up their positions on their respective hills.
    
        The two generals must have their armies attack the city at the same time in
        order to succeed. They must thus communicate with each other to decide on a
        time to attack and to agree to attack at that time, and each general must know
        that the other general knows that they have agreed to the attack plan. Because
        acknowledgement of message receipt can be lost as easily as the original message,
        a potentially infinite series of messages is required to come to consensus.
    

<http://en.wikipedia.org/wiki/Two_Generals%27_Problem>

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chime
I agree. Looks like the submitter is thinking of Two Generals. It's closely
related to BFT ( <http://en.wikipedia.org/wiki/Byzantine_fault_tolerance> )
which does have some pretty complex solutions. Friend of mine wrote a paper on
improving BFT for his PhD thesis.

