A computer network allows two or more computers to communicate through connected communication devices and links. For effective communication, all participating computers must follow the same set of protocols which define the communication rules. Protocols allow different computers from various vendors to understand each other. Networks can be classified based on their geographic range and access as LANs, MANs or WANs, and private or public networks. They can also use point-to-point or broadcast models and employ circuit switching or packet switching technologies.