1. Objectives
In cases where devices such as power meters must be installed in a remote location
(e.g., in a mountainous region), a fixed PSTN or Ethernet network connection may
not be available. In order to retrieve real-time and historical data from devices that
are installed in remote locations, it is usually possible to install a wireless modem at
the remote site. This document gives a basic example of how to set up an ION
Enterprise power monitoring system to communicate with a remote device that is
connected using a wireless (GPRS) modem.
The setup is almost identical to the situation where a traditional analog modem is
used to connect to the meter. The main purpose of this document is to highlight the
additional settings needed when using wireless (GPRS) modems. Those people who
have experience in connecting to a meter using analog modems (or embedded
modems in the meter communication card) may ignore all sections other than the
section describing wireless modem setup.
Background Information
1. What is GPRS, and how is it different from GSM?
GSM and GPRS refer to connection methods used by cellular (mobile) phone
networks. The devices used to communicate (i.e., mobile phones or wireless
modems) are the same, as is the physical communication medium (air), but the
underlying mechanisms for data transfer are different.
Source: http://www.mobile-phones-uk.org.uk/gprs.htm
Whilst GSM (2G) networks are excellent for voice calls, they are limited when it
comes to sending and receiving data. GSM phones use a technology called CSD
(Circuit Switched Data) to transfer data. CSD requires the phone to make a special
connection to the network before it can transfer data (like making a voice call) which
can take up to 30 seconds. Once connected, the data is sent or received and the
user is billed for the time spent online. Data transfer is relatively slow: 14.4 kbps
(kilobits per second) for GSM 1800 networks (Orange and T-Mobile) and 9.6 kbps for
GSM 900 networks (Vodafone and O2).
GPRS (General Packet Radio Service) is a method of enhancing 2G phones to
enable them to send and receive data more rapidly. With a GPRS connection, the
phone is "always on" and can transfer data immediately, and at higher speeds:
typically 32 - 48 kbps. An additional benefit is that data can be transferred at the
same time as making a voice call. GPRS is now available on most new phones.
Because GPRS transmits data in packets, the timeslots are not in use all the time,
but are shared amongst all users of the network. That increases the overall data
capacity of the network, and it also means that you are billed for the quantity of data
transmitted, not the time that you are online. It may mean that during busy times,
data transfer rates slow down, because the network will give priority to voice calls.
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