In this section you will find various industrial grade routers that use PSTNmodem technology to communicate over a wide area network (WAN). PSTN is an acronym for Public Switched Telephone Network, which is a general term used for a group of switched line modem technologies. Switched line modem technologies include 56k V.90 / V.92 and ISDN, which were popular in the commercial marketplace in the 1990s before the advent of broadband. However, the products found in this section are not commercial grade, they are designed to be used in industrial applications. Features such as DIN rail mounting, DC power, wide operating temperature ranges and rugged enclosures are commonplace.