Computer modems have evolved a lot over the past few decades and now offer much higher speeds and greater functionality. These hardware devices are what connect a computer (and often the network it is a part of) to the Web. ADSL modems use copper telephone lines to transfer data unlike 3G modems, which use mobile networks to do the same job. Another type of wired modem that you might encounter is the cable modem, a hardware device that connects to the Internet via a cable TV line.Types of ADSL
The two main types of ADSL in use are ADSL2 and ADSL2+. The major difference between the two is speed. ADSL2+ offers twice the maximum download speeds as compared to ADSL2, going as high as 20 Mbps. Modems designed for ADSL2+ work with an ADSL2 network as well, but those designed for ADSL2 may not exploit the full potential of ADSL2+.Types
While some ADSL modems only offer the ability to connect to the Internet, most consumer devices also combine a router in the same device. This means that the one device will both access the Web and offer a means to create a local network.Router Connectivity
ADSL modems that include a router will have a number of Ethernet ports. The more the number of ports, the more computers you can connect to the local network directly. In addition, some routers offer Wi-Fi functionality. This means that you can set up a local wireless network as well, all with just one device.Downstream Speeds
While the speed of the modem's connection to the Web is fixed based on what the provider offers, it is the modem that controls the speeds at which devices in the local network connect to it (and to each other). For wired Ethernet connections, the fastest is Gigabit Ethernet, which supports a maximum rate of 1 Gbps (1000 Mbps). Wi-Fi connections have different standards, some of the latest being the 802.11ac and 802.11n. Specifically, an ADSL router that offers an 'n' Wi-Fi connection can support data speeds from 54 Mbps to 600 Mbps.