User`s guide

1-5
• If the cellular account includes a feature called SMS (short message service), the
computer can send a text message to the DCM-200. When the DCM-200
receives the message it will immediately call back as described in Scenario #1.
1.4 CSD Versus Packet Mode
The DCM-200 can communicate with the central computer’s modem using a circuit-
switched data (CSD) connection, or can use the general packet radio standard (GPRS)
to exchange information with the central computer over the Internet. There are
advantages and limitations to each method.
CSD mode is similar to two modems communicating over a wired telephone line. The
cellular service provider has a bank of modems available in their switching centers.
When it detects a CSD call, it connects one of its own modems to the wired line. Data is
transferred between the DCM-200 and the switching center over the radio link, and then
between the switching center and the destination modem via wire. Cellular service
providers often offer this service as an add-on package to a standard “voice” account,
and each call is measured and billed in terms of minutes used. Depending upon the
frequency and length of the calls this service can become quite expensive. In situations
in which the calls are long distance, it may be possible to purchase plans that include
free long distance in order to reduce costs.
The cellular service provider may offer access to the Internet using a service called
GPRS (general packet radio service).
Data is exchanged in small blocks, or packets, to
a server running Metretek’s DC-2000 software.
Cellular service providers may offer this
service as an add-on package to a standard “voice” account, or may offer it as a stand-
alone product. Each connection is measured and billed in terms of the amount of data
exchanged, usually in increments of 1 million bytes (1 Mb) per month. The amount of
information exchanged on each call may range from several hundred bytes to 10’s of
thousands of bytes, depending upon the information that is requested from the electric
meter. It may be necessary to test the system for several months and then adjust the
cellular account for the best cost based on your needs.