Source-Independent path in graph
===

Some years ago I read about an algorithm: it labels graph's edges so path from source node X to destination node Y is always the same sequence of labels, independently from which node you select as source X. How is it called?

(I can't remember which kind of conditions should be satisfied by graph)

Here an example (created by me):

![Example graph][1]

- Vertex 1: Red/Black/Red
- Vertex 2: Red/Red/Black
- Vertex 3: Red/Red/Black/Green
- Vertex 4: Red/Black/Red/Green

Starting from any vertex as source you using the path above you always reach the destination vertex. 

  [1]: http://i.stack.imgur.com/uH6y6.png