Specifications

Rockwell Automation Publication AG-SG001G-EN-P - April 2015 25
Choosing a Telemetry Network Chapter 2
Public-switched Telephone Network (PSTN) or General
Switched Telephone Network (GSTN)
The dial-up network is furnished by a telephone company. This telephone line is
the one that we use daily and that carries voice and data transmissions.
Advantages/Capabilities
• Public-switched telephone networks are cost-effective for:
– short, occasional data collection from remote sites that have access to a
PSTN.
– sites calling in to a central location.
• Often point-to-point applications have a dial-up connection as a backup to
the main media link.
• The phone company charges a monthly fee based on usage – the number
of local connections made and/or the time and distance of each long
distance connection.
• The network supports communication rates of up to 57,600 bps.
• The network is a 2-wire connection that supports half-duplex modems and
2-wire, full-duplex modems. The topology is point-to-point.
Disadvantages
• Transmission is costly for long, frequent data collection from remote sites.
• The lines can contain impairments that can cause modems to have error
rates of less than 1 error per 1,000,000 bits.
• The media cannot be used in areas that do not have access to the network,
such as an offshore oil or gas well.
• Time is required to dial and establish each connection.
• Additional logic is required to automatically initiate a connection.
Equipment Required
Use standard Bell or Consultive Committee for International Telephone and
Telegraph (CCITT) modems. Contact the telephone company for information
about connecting to the network.
%%