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ISDN is now more than 20 years old, and there's been quite a lot of progress in the computer business in the interim. Network manager have found that ISDN's ability to operate as a Wide Area Network often is not needed because now it is not only possible to put 128K on a pair of a copper wires, but the wires depending on their length and condition, can accommodate up to several millions bit per second.

The 1990's response to ISDN is Digital Subscriber line, which comes in several varieties. Asymmetrical DSL is a popular Metropolitan Area Network for individuals and small business. It's asymmetrical because the Downstream speed is faster than the Upload speed, typically 1 Mbps Downstream and 256 Kbps Upstream, with a distance limit of about 3 miles from the central office to the customer. ADSL can share a single pair of wires with a regular phone line, But in practice, because a customer's ISP usually arranges for his ADSL, service, many phone companies refuse to bill phone service to the phone user and ADSL to another user on the same wires. The longer the wire from the phone company's central office to the customer, the slower the maximum speed that ADSL can provide. At times, a line maybe too long to support ADSL.Unlike regular phone service, DSL is unswitched, which means that it gives dedicated connection to ISP's.

ADSL lines run from local phone company central offices to businesses, and data may travel from an ADSL line to an Internet provider in several ways. Installing an ADSL modem on each ADSL line, which splits the regular phone lines from the DSL data, is the official technique. In this process, phone lines are connected to a phone switch, and the DSL data lines are connected to a DSL Access Multiplexor (DSLAM). A DSL Access Multiplexor combines the data from an ISP's customers unto a faster connection to the ISP.

Another approach is for an ISP to rent dry pairs, unconnected phone wires, and run ADSL on them. An ISP then can run DSL data directly into a TCP/IP router. The ISP rents dry pairs that run between its office and the phone company. The ISP then rents long dry pairs out to its customers and just ties the two dry pairs together at the phone company's central office. the sort pairs are cheap, and the ISP's avoids having to pay to use the phone company's DSLAM. The ISP also avoids having to rent expensive space at the phone company's central office for a router. This only works in areas where phone companies still sell dry pairs, a service originally intended for burglar alarm circuit, which phone companies are trying to phase out. In other places the ISP has to order an official ADSL line and arrange to hook it to a DSLAM. Otherwise it may need to rent space at the phone company's central office for a router.

Although ADSL is the most common type of DSL used for Internet access, there are a couple of other kinds. Symmetrical DSL), provides connections at up to several millions bits per second over two pairs of wires, with both directions transporting data at the same speed. It's more expensive and les widely available than ADSL, and it usually is used for connecting corporate networks to the net. High speed DSL , and High speed DSL2 also are symmetrical systems. They run at 1 Mbps.

A few phone companies provide so called IDSL , which is an ISDN connection that's always dialed-up. IDSL is technically inferior to other kinds of DSL.