A bridge is a device that connects two or more physical networks and forwards packets between them. Bridges can usually filter packets - that is, forward only certain traffic. Routing Information Protocol, a type of protocol a router can use to communicate with other routers. A formal description of message formats and the rules two or more systems must follow to exchange those messages. Protocol definitions range from how bits are placed on a wire to the format of an e-mail message.
Standard protocols allow different manufacturers' computers to communicate.
The computers can use completely different software, provided each computer's software can agree upon the meaning of the data. Simple Mail Transfer Protocol, the Internet e-mail protocol.