Principles Digital Communication System & Computer Networks (Charles River Media Computer Engineering)

24.5 INTERNET ACCESS PRODUCTS

To access the Internet, the user has to be connected to the server of the local ISP. This access can be through a dial-up line, a digital subscriber line, or wireless links.

Dial-up lines: The dial-up connection can be a regular PSTN line, in which case the data rate is generally limited to about 56kbps. Alternatively, ISDN lines can be used that support higher data rates up to 128kbps.

Dial-up lines and ISDN lines are used extensively for Internet access. The family of digital subscriber lines such as HDSL and VDSL provide dedicated high-speed connection between the subscriber and the Internet service provider. Present access speeds using the DSL technologies are up to 50Mbps.

Digital subscriber lines (DSL): Nowdays, DSLs are being provided between the subscriber premises and the ISP premises. DSLs with various speeds are available, which are collectively referred to as xDSL. Using HDSL (high data rate digital subscriber line), data rates up to 2Mbps are now possible. DSL can provide a dedicated connection between the ISP and the subscriber, and so the subscriber is always connected to the Internet. The latest in the DSL family is VDSL (very high speed DSL). Using VDSL, speeds up to 48Mbps can be achieved if the distance is no more than 300 meters and up to 25Mbps if the distance is no more than 1500 meters, with 0.5mm copper cable. Soon, fiber to home will be more widespread, which will support much higher data rates.

Wireless access to the Internet: With the popularity of mobile phones and PDAs, accessing the mobile network through wireless devices is catching up very fast. Though access speed with the present wireless networks is about 14.4kbps, in the near future access speeds up to 2Mbps are feasible with the third generation (3G) wireless networks.