C H A P T E R 15
• Describe the history of dialup technology.
• Describe dialup connectivity technology.
• Describe the different types of dialup methods.
• Discuss the benefits (and drawbacks) of different dialup technologies.
Dialup is simply the application of the Public Switched Telephone Network (PSTN) to carry data on
behalf of the end user. It involves a customer premises equipment (CPE) device sending the telephone
switch a phone number to direct a connection to. The AS3600, AS5200, AS5300, and AS5800 are all
examples of routers that have the capability to run a PRI along with banks of digital modems. The
AS2511, on the other hand, is an example of a router that communicates with external modems.
Since the time of Internetworking Technologies Handbook, 2nd edition, the carrier market has continued
to grow, and there have been demands for higher modem densities. The answer to this need was a higher
degree of interoperation with the telco equipment and the refinement of the digital modem: a modem
capable of direct digital access to the PSTN. This has allowed the development of faster CPE modems
that take advantage of the clarity of signal that the digital modems enjoy. The fact that the digital
modems connecting into the PSTN through a PRI or a BRI can transmit data at more than 53 K using
the V.90 communication standard attests to the success of the idea.
A Short Dialup Technology Background
Dialup technology traces its origins back to the days of the telegraph. Simple signals being sent across
an extended circuit were created manually by tapping contacts together to turn the circuit either on or
off. In an effort to improve the service, Alexander Graham Bell invented the telephone in 1875 and
changed communication forever. Having the capability to send a voice across the line made the
technology more accessible and attractive to consumers. By 1915, the Bell system stretched from New
York to San Francisco. Demand for the service drove techno