Specifications

56 Rockwell Automation Publication AG-SG001G-EN-P - April 2015
Chapter 3 Choosing Data Communication Equipment
Two major components of the cellular network are the remote site and the host or
central site. The remote site has application devices locally networked and
communicate to the host site by using the cellular network through a gateway.
These devices could be a PLC or other equipment like an embedded computer.
The host site runs an application server that could be a web server that is
responsible for running the application.
Depending on the application of the cellular network, a cellular network may be
organized as Mobile Originated mode, Mobile Terminated mode, or Both
Mobile Originated and Terminated mode.
In the Mobile Originated mode, the remote device or node initiates a connection.
This connection is terminated at the host, usually at the host web server. In the
Mobile Terminated mode, a host will request or poll for information from the
remote device. In this case, the host device initiates the connection and the
connection is terminated at the remote site. In the Both Mobile Originated and
Terminated mode, the host and the remote site are able to initiate connections.
Usually, the host will poll for information from the remote site, but the remote
site is also proactively able to send out event and alarm information to the host
site.
To use the cellular modem technology effectively, a user has to have the following
components:
Data plan subscription
Cellular modem
The user needs to make sure that the cellular modem purchased for the network
is compatible with a good cellular service provider's plan. As mentioned above,
there are two very popular cellular technology types namely GSM and CDMA.
Verizon Wireless, Alltel, and Sprint use CDMA. T-Mobile and AT&T use the
GSM cellular format. Often, CDMA may be referred to as or associated with W-
CDMA, EV-DO, and EV-DV, while GSM/GPRS may be associated with EDGE
or EGPRS.
Below are some considerations to be made before finalizing a cellular modem and
plan purchase:
Ensure that the manufacturer of the cellular modem device offers technical
support and other regular update services.
If you are expecting certain areas to have low connectivity issues, purchase a
signal booster or repeaters to enhance data reception.
Understand the different cellular providers' plan options in the target
areas.
Choose a carrier that offers the maximum reception coverage in the target
areas. Most carriers have interactive websites with geographic maps that
you can use to determine coverage in your area.
Some cellular modem providers have dedicated contacts with the cellular
providers who can facilitate and make cellular account set up easier.