Unreliable Connection

Logic Level 3

Alice and Bob both want to send each other a message over an unreliable connection. They've agreed on a protocol whereby Alice will go first and keep sending her message until she gets a message from Bob. Likewise, Bob will wait until he receives a message from Alice then keep sending his message until he gets an acknowledgement message from Alice.

And so forth...

What is the minimum number of messages that need to be sent so both Alice and Bob are sure that both Alice and Bob are sure that their messages have been read?

Assume there's a 100% reliable connection.


The answer is 4.

Garrison Wynn by Garrison Wynn , 40, United Kingdom

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Garrison Wynn
Dec 28, 2015

Let's assume a 100% reliable connection, Although Alice and Bob don't know this.

  1. Alice sends message 1, Bob receives it, but Alice doesn't know this yet.
  2. Bob sends message 2, Alice receives it and is now sure that Bob has read her message, but Bob doesn't know this yet.
  3. Alice sends message 3, Bob receives it and now becomes aware of 2 things. Firstly, his message (2) has been read, and Secondly that Alice is sure her message (1) has been read, But Alice does not know that Bob is sure that his message has been read.
  4. Bob sends message 4, Alice receives it and now she knows that Bob knows that his message has been read.
7 Helpful 0 Interesting 0 Brilliant 0 Confused

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...