Dialup WAN access may be required when no other WAN technology is available. For example, a remote location could use a modem and analog dialed telephone lines to provide low capacity and dedicated switched connections. Dialup access is suitable when intermittent, low-volume data transfers are needed.
Traditional telephony uses a copper cable, called the local loop, to connect the telephone handset in the subscriber premises to the CO. The signal on the local loop during a call is a continuously varying electronic signal that is a translation of the subscriber voice into an analog signal.
Traditional local loops can transport binary computer data through the voice telephone network using a modem. The modem modulates the binary data into an analog signal at the source and demodulates the analog signal to binary data at the destination. The physical characteristics of the local loop and its connection to the PSTN limit the rate of the signal to less than 56 kb/s.
For small businesses, these relatively low-speed dialup connections are adequate for the exchange of sales figures, prices, routine reports, and email. Using automatic dialup at night or on weekends for large file transfers and data backup can take advantage of lower off-peak tariffs (toll charges). Tariffs are based on the distance between the endpoints, time of day, and the duration of the call.
The advantages of modem and analog lines are simplicity, availability, and low implementation cost. The disadvantages are the low data rates and a relatively long connection time. The dedicated circuit has little delay or jitter for point-to-point traffic, but voice or video traffic does not operate adequately at these low bit rates.
Note: Although very few enterprises support dialup access, it is still a viable solution for remote areas with limited WAN access options.