The main disadvantage of this approach lies in the contention for the phone lines between voice and data, and the cumulative cost of all the additional phone lines that would end up being dedicated to modem use. A major limitation of this approach is that it does not support the ability to provide services on the Internet. If you want to have a Web server or other resource that can be accessed on the Internet, then you need a full-time dedicated connection. The more functional model of connecting to the Internet involves establishing a link between your local network and the Internet, rather than providing Internet access to individual computers. To enable this model of connectivity you would use a device called an router.
Large networks have sophisticated routers that manage multiple internal and external connections.
Small networks typically use much simpler, scaled-down devices called access routers. An access router would have an Ethernet port that connects to your local network and another port that connects to the link to your ISP and is equipped with simplified routing software that can be easily configured. Routers are devices that help networks connect efficiently. We noted earlier that networks pass information in packets. A router examines each packet on the network and makes decisions about the quickest way to get it to its destination.