In the previous tutorial, the Ethernet technology was used to connect an Arduino based IOT device with the internet network. The IOT devices can also be connected to internet network using mobile technologies like GSM, CDMA and GPRS. There are two major technologies for data transfers over cellular networks – GSM and GPRS. These two technologies differ from each other on the basis of data rates and the charges they take for their operation.
GSM (Global system for mobile communication) is one of the most successful second generation cellular technologies. It is used for mobile communication, but the major drawback of this technology is the low data rates i.e. GSM was initially developed to transfer the packets at low rates up to 14.4kbit/s. GSM is based on circuit switched technology in which the user’s running cost is based on how long the connection is made (i.e. circuit is closed) regardless of the amount of data sent.
On the other end, GPRS (General Packet Radio Service) is an upgraded version of GSM with the feature of high speed data rates up to minimum of 85.6 kbit/sec. It enables the users to connect to the Internet so that they can easily browse websites, can interact with multimedia sites, can take part in video conferences and similar applications using mobile devices as well as computers. GPRS is based on packet switching technology in which user’s running cost is based on the amount of data sent (no. of packets) regardless of connection time. It allows the network to transmit IP packages to external networks. This technology became the intermediary between second-generation GSM cellular technology and 3G W-CDMA/UMTS system. This service is compatible with 2G and 3G networks.
GPRS Communication Mechanism –
GPRS is based on IP communication and the connected unit must provide an IP address before a connection can be established. For this the mobile phone or laptop must be connected to the GPRS network. A dynamic IP should be assigned to the mobile device and only after that the exchange of data over GPRS takes place.
Fig. 1: Image showing GPRS Communication Mechanism
Benefits of GPRS technology –
GPRS technology is playing a vital role in the field of cellular network communication. It has a number of advantages for users and network operators over the GSM system as follow –
• Speed – One of the great advantages of GPRS technology is that it offers a much higher data rate as compared to GSM system. The maximum range, GPRS can provide is 172 kbit/second in 3G system where as for 2G system, GPRS provides 56-114 kbit/sec.
• Packet switched operation – Unlike GSM which is based on circuit switched techniques, GPRS technology uses packet switching in line with the Internet. This technology provides greater advantage to GPRS when it merges with Internet techniques.
• “Always On” connectivity – Another advantage of GPRS is that it offers an “Always On” capability. As GPRS is based on packet switched technique, the user pays charges for the amount of data carried by him/her whereas GSM is based on circuit switched technique in which charges are based on the time of the use of circuit i.e. how long the call is!
• Instant messaging and presence – Due to greater data speed of GPRS, the messaging between two devices is done extremely fast in GPRS. If SMS is sent over GPRS, the SMS transmission speed of nearly 30 SMS per minute can be achieved, whereas with GSM the SMS speed is only about 6-10 SMS per minute. The speed difference can be observed by using GPRS as well as GSM.
The GSM and GPRS are the two faces of a single coin called a system, though they are operated separately. The GSM technology carries the voice calls and text messages, while the GPRS technology is used to transfer the data along with voice and text messages. Collectively, this system is referred as GSM GPRS system. The GPRS is a best-effort service which implies variable through and latency that depend on the number of users sharing the service simultaneously.
SIM800 Module –
The IOT devices can be connected to a GSM GPRS network by interfacing them with a GSM GPRS modem. One of the popular GSM GPRS modem is SIM800 module that has full flexibility of GSM/GPRS features. It supports Quad-band frequency of 850/900/1800/ 1900MHz. It can transmit voice, SMS and data information with low power consumption. It provides serial UART communication over AT commands with computer or microcontroller.
Fig. 2: Typical Image of SIM800 GSM GPRS Modem
The SIM800 Modem has the following features –
• Quad-band 850/900/1800/1900MHz
• Bluetooth: compliant with 3.0+EDR
• Control via AT commands
• Supply voltage range 3.4~4.4V
• Low power consumption
There are many more features of SIM800 available. The features that must be known for using the module are mentioned above. In the next tutorial, learn about how SIM800 Modem can be configured to connect with the GSM GPRS network using a PC as TCP-IP server.
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