User`s guide

4-1
4 CELLULAR SERVICE
4.1 GSM Service
4.1.1 GSM Overview
GSM is an abbreviation for Global System for Mobile communications. This
communications standard is widely used throughout Europe, Africa, Asia and parts of
North and South America. Messages are digitized into packets and sent in brief bursts
during allocated time slots using a variation of TDMA (Time Division Multiple Access)
techniques. Up to 8 cellular phones can thus share the same frequency band, which in
turn permits the system to support more users with existing equipment. Efficient
utilization of spectrum is an important consideration for service providers since there is
only a limited bandwidth space that has been allocated to cellular phone service.
Most GSM systems throughout the world operate on either the 900 MHz or 1800 MHz
communications bands. In North America most GSM systems began operation on the
1900 MHz band. Older analog cellular services on the 850 MHz band are now also
being converter to GSM.
4.1.2 Establishing cellular service for GPRS
A cellular account must be activated with a cellular service provider prior to placing a
DCM-200 into service. Some GSM service providers may not offer all forms of data
transfer. General packet radio service (GPRS) may have to be added to a standard
voice plan, or may be a stand-alone service.
GPRS packages are generally priced by the number of bytes to be transferred, rather
than by the minute. Typically, the smallest available package will be 1 megabyte (1 Mb)
per month. The amount of data that the DCM-200 will produce depends upon how the
device is configured and what sort of data is requested from the electric meter. The
amount of information exchanged on each call may range from several hundred bytes to
10’s of thousands of bytes. 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.
In order to connect to the Internet, the cellular service provider has its own computer
equipment called a “gateway” server. The server will have an “APN” (access point
name), usually in the form of a domain name, such as
“internetaccess.providername.com”. Contact your service provider for this information.
This APN will be needed when configuring the DCM-200 (Chapter-5).
Service providers may have several different gateways to choose from, depending upon
the type of service required. “Web phones” (cellular phones that support Internet
access) are generally assigned to a gateway that only connects to WAP services
(wireless application protocol). The DCM-200 requires full Internet access because
the data collection software could be running on any server located anywhere in
the world. Full access gateways are usually assigned to customers who will be
connecting a wireless modem to a personal computer.