When intermittent, low-volume data transfers are needed, modems and analog dialed telephone lines provide low capacity and dedicated switched connections.

Traditional telephony uses a copper cable, called the local loop, to connect the telephone handset in the subscriber premises to the public switched telephone network (PSTN). The signal on the local loop during a call is a continuously varying electronic signal that is a translation of the subscriber voice.

The local loop is not suitable for direct transport of binary computer data, but a modem can send computer data through the voice telephone network. The modem modulates the binary data into an analog signal at the source and demodulates the analog signal at the destination to binary data.

The physical characteristics of the local loop and its connection to the PSTN limit the rate of the signal. The upper limit is around 33 kbps. The rate can be increased to around 56 kbps if the signal is coming directly through a digital connection.

For small businesses, this can be 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 (line 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 provided by dialup will have little delay or jitter for point-to-point traffic, but voice or video traffic will not operate adequately at relatively low bit rates.

Interactive Media Activity Checkbox: WAN Technologies Analog Dialup Upon completing this activity, the student will be able to identify the characteristics associated with an analog dialup circuit.

   

Web Links Dialup Technologies http://www.cisco.com/univercd/cc/ td/doc/cisintwk/ito_doc/ dialup.htm