|  | 8.8 | Remote Connectivity
| 8.8.3 | The attributes, advantages and disadvantages of ISDN and PSTN (POTS)
The Public Switched Telephone Network (PSTN) was originally designed to carry analog voice signals across telephone lines. A technology called Integrated Services Digital Network (ISDN) was created to convert analog signals into digital signals to allow data transfer rates faster than PSTN. An advantage of ISDN over PSTN is speed. The fastest connection a modem can establish using a PSTN analog line is 56 Kbps. Data is converted by the modem from the PC's digital signals to analog signals, then sent across the wires to a remote network, where the data is again converted from analog signals to digital signals. ISDN enables digital signals to travel over regular telephone lines in its digital form; transmitting data in half the time of analog modems. An ISDN BRI line can carry data at 128 Kbps, and ISDN BRI lines can be aggregated to create an ISDN PRI line to carry 1.472 Mbps(T1) or 1.920 Mbps(E1). Another advantage of ISDN over PSTN is the ability to be connected to the network "all the time" without tying up the analog telephone line, which is especially useful for telecommuters.