Figure one shows the role of protocols in data transfer.  The role here is to forward data packets across a network.  The example shows a router reading a message because it understands the I P version four header and therefore can process it. Figure two shows routers sharing information about pathways to other networks.  It is common for routers to share information. Figure three shows routers communicating with each other regarding a slow path due to another path that is down, this sharing of information is critical to a network. Figure four shows the setup and termination of a data transfer session between a host and a server.