The need for a single, reserved circuit from end-to-end does not exist in a packet switched network. Any piece of a message can be sent through the network using any available path. Additionally, packets containing pieces of messages from different sources can travel the network at the same time. By providing a method to dynamically use redundant paths, without intervention by the user, the Internet has become a fault tolerant method of communication. In our mail analogy, as our postcard travels through the postal system they will share transportation with other postcards, letters and packages. For example, one of the postcards may be placed on an airplane, along with lots of other packages and letters that are being transported toward their final destination.