Specifications

Rockwell Automation Publication AG-SG001G-EN-P - April 2015 27
Choosing a Telemetry Network Chapter 2
Digital Data Services (DDS)
DDS is a special wide-bandwidth private leased line that uses digital techniques
to transfer data at higher speeds and at a lower error rate than private leased lines.
The line is available 24 hours a day.
Advantages/Capabilities
• DDS is a digital network that offers higher transmission rates and
minimal, if any, line impairments.
• The media is useful when an application requires very large amounts of
data to be transferred between sites with a low data error rate.
• Regardless of use, the phone company charges you a flat, monthly fee based
on the following:
– Distance between sites
– Area of the country
– Speed of the integrated service unit (digital ‘modem’)
• A constant connection exists.
• Asynchronous communication rates are 2.4 K, 4.8 K, 9.6 K, 19.2 K,
38.4 K, and 57.6 Kbps.
• The network provides a four-wire connection and can be configured in a
multi-drop topology.
Disadvantage
The media is costly for applications not needing to transmit large amounts of
data quickly and at a low data error rate.
Equipment Required
Use standard integrated service unit, ISU (also called a data service unit [DSU]
or channel service unit [CSU]). The ISU data rate must match that of the digital
data service line, which operates at a fixed rate.
Phone Company
DDS DDS