This is a fun thought-experiment highlighting the challenges of communicating over an unreliable channel — where your message may or may not get through, and where you won’t know if it has.

The situation is that two armies, either side of a hostile valley, are trying to coordinate an attack, and they want to attack at the same time to be sure to succeed. The trouble is, to coordinate they have to send brave messengers through the hostile valley to the other camp and the messengers may or may not be captured along the way.

To coordinate the attack you have to know that your message got through which you’d know if you received a confirmation. But how would the general sending the confirmation know that their confirmation got through unless they received a confirmation of the confirmation. And on…

The two generals problem

The value of a telecommunications network is proportional to the square of the number of users of the system.
— Robert Metcalfe

This law explains a little of the remarkable power of a growing network. Each time you add a user, or node, to the network, the number of connections increase in proportion to the square of the number of users. So, in this simple example where every new node gets a connection to each of the existing nodes, you can see that, say, adding a single node to an 11 node network creates 11 new connections.

It’s a simplified example because in most networks the value is not directly proportional to the number of connections as some connections or users may be more valuable than others, and usually adding a new user wouldn’t create a connection to all existing users — say if it was in a different country, or people spoke a different language, or just cared about different things. But nevertheless, you can see how a network quickly becomes valuable as users join.

So, Facebook has about 2 billion users…

Metcalfe was talking about telecommunications networks and the basic proposition has been modified since it was formulated including by Metcalfe himself.

Once again, just because something is called a law doesn’t mean it is one. See Fitt’s Law

Metcalfe’s Law

When you're next at a conference try starting 3 mindmaps: one for Questions, one for People and one for Ideas.

I have found this technique helps me with both getting the most out of the event at the event, and getting the most out of the event after the event.

Starting a to-do list on the side doesn’t hurt either.

Sketchplanations tagged with networking