ISDN is still a dial-up connection, but it has a few key differences. ISDN is a digital connection that is used over regular lines. An ISDN line is made of two regular copper telephone lines, each with their own phone number so they can be used with regular telephones. Because ISDN is dial-up, it means that the telephone line can not be used by both a ISDN connection and a telephone. The advantages of being digital is that the connection is 64k for each line, connect rates are always at 64kbps, ISDN signals can be processed by routers, bridges and hubs. The disadvantages are that special offload circuits have to be installed into the telephone line, and like DSL, ISDN is range limited. ISDN is limited to 18000 cable feet for a connection to be possible. ISDN connections can use either 1 or 2 phone lines using inverse multiplexing. While using only one line, the maximum speed is 64k, and for 2 lines it is double at 128k. A typical 128k connection uses two 64k bearer (B) channels and one 16k delta (D) channel for a controller. Because ISDN needs a controller, in some areas that have older telephone switching equipment, the controller has to share the same bandwidth as the data. This results in a 56k single line connection and a 112k double connection. ISDN never caught on for consumer level because it suffers the same range restrictions as DSL, but offers only a fraction of the speed. Although this connection is only 64k or 128k, because it is a digital signal, throughput is always 8k or 16k respectively for both uploads and downloads. The digital signal also allows for lower ping times, around double that of a cable or DSL connection.

DSL was developed to be broadband connection that could compete with cable. DSL uses standard phone lines to send analog signal link a regular modem, but uses the unused frequencies for greater bandwidth. Regular phones use the frequencies between 0-4KHz, while DSL often use the frequencies between 26KHz and 1MHz. DSL signals are filtered out before the PSTN processing occurs. This means that DSL modems are capable of using all of the frequency ranges like a cable modem is, except for the small portion that a standard phone uses. Because DSL modems do not use the standard telephone or standard modem frequencies, the phone line can be used simultaneously between the two. And because DSL signals do not have to travel through PSTN, they do not have to dial in to make connections.

DSL is dedicated bandwidth, unlike cable, and offers multiple speed grades, depending on the users distance from the PSTN telephone office. High bandwidth in excess of 2Mbps are capable withing 12000 miles of the PSTN, but available bandwidth diminishes the farther away from the PSTN the user is. The maximum distance that DSL is able to operate at is 18000 cable feet from the PSTN. This is because, unlike coaxil cable lines, phone lines were not designed to handle high bandwidth signals. The greater distance the signal has to travel, the more interference it will have. Interference disrupts the high frequency ranges, so they may become too distorted for use at long or even moderate distance.

DSL comes in many different variations, the most popular is Asynchronous DSL, which offer different speeds for upload and download, making is more economical for the average user. DSL connections are cable of very low pings, in the ranges of sub 10ms.

Dial-Up Phonelines | ISDN and xDSL | Cable, Satellite, & Shotgun