A key difference that can be observed between Internet and DTN routing is that Internet routing is based on packet forwarding. Whereas in DTN, routing mostly involves message replication. A node in DTN, which wants to transfer a message to the other node in contact, creates a copy of that message and forwards that * copy * to the other node. This process is repeated at every (or limited # of) node(s) until the message reach its destination. In Internet it is only the sender who buffers the message until an acknowledgement is received from the other end of the connection. Epidemic and Spray-and-Wait are two popular DTN routing protocols using such principle. Epidemic protocol replicates the message at every node it comes in contact with. Spray-and-Wait imposes certain limit on the # of replications to be done.