Routers are even more intelligent than switches.
Routers read each packet and send it over the most efficient path possible to the appropriate destination according to a table of rules. This greater intelligence, though, requires more processing, making routers less efficient than switches or hubs. Routers are most often used to connect geographically separated networks using relatively low-speed technologies, such as ISDN or T1 lines. The branch-office router is the lifeline back to headquarters. Because WAN bandwidth is expensive, the router uses data compression and knows when to keep local area network traffic from going out over the connection to the main office.