Carrier sense multiple access with collision detection or CSMA/CD is a protocol (or rule) used by computer ethernet networks. It stops computers from sending information on the same ethernet wire at the same time. With this rule, a computer will check that the wire is not being used before it sends information. This ability to check is called "carrier sense." This rule is used when many computers can use the same connection. This is called "multiple access." If computers do send information at exactly the same time, the computers can tell a mistake has been made and stop sending. This is called "collision detection." When this collision occurs, the computers stop sending information, wait for a random amount of time, and then check before resending the information.