Embedded Systems, Mechatronics and Virtual Instrumentation

Embedded Systems - Mechatronics
Virtual Instrumentation

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Frequently Asked Questions

What are GSM, GPRS and SMS?
What is a Real-Time System?


GSM (Global System for Mobile communications: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. Its promoter, the GSM Association, estimates that 82% of the global mobile market uses the standard. GSM is used by over 3 billion people across more than 212 countries and territories. Its ubiquity makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs from its predecessors in that both signalling and speech channels are digital, and thus is considered a second generation (2G) mobile phone system. This has also meant that data communication was easy to build into the system.

The ubiquity of the GSM standard has been an advantage to both consumers (who benefit from the ability to roam and switch carriers without switching phones) and also to network operators (who can choose equipment from any of the many vendors implementing GSM). GSM also pioneered a low-cost (to the network carrier) alternative to voice calls, the Short Message Service (SMS, also called "text messaging"), which is now supported on other mobile standards as well. Another advantage is that the standard includes one worldwide Emergency telephone number, 112. This makes it easier for international travellers to connect to emergency services without knowing the local emergency number.
Short Message Service (SMS) is defined as a text-based service that enables up to 160 characters to be sent from one mobile phone to another. In a similar vein to email, messages are stored and forwarded at an SMS centre, allowing messages to be retrieved later if you are not immediately available to receive them. Unlike voice calls, SMS messages travel over the mobile network's low speed control channel.
"Texting", as it is also known, is a fast and convenient way of communicating. In fact, SMS has taken on a life of its own, spawning a whole new shorthand language that is rapidly being adopted as the norm.

Newer versions of the standard were backward-compatible with the original GSM phones. For example, Release '97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS) which allows packet based Internet connections. Release '99 introduced higher speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE).

The network behind the GSM system is divided into a number of sections as shown by the picture below.

GSM Network

  1. The Base Station Subsystem (the base stations and their controllers).
  2. The Network and Switching Subsystem (the part of the network most similar to a fixed network).
  3.  This is sometimes also just called the core network.
  4. The GPRS Core Network (the optional part which allows packet based Internet connections).
  5. All of the elements in the system combine to produce many GSM services such as voice calls and SMS.

One of the key features of GSM is the Subscriber Identity Module (SIM), commonly known as a SIM card. The SIM is a detachable smart card containing the user's subscription information and phone book. This allows the user to retain his or her information after switching handsets. Alternatively, the user can also change operators while retaining the handset simply by changing the SIM. Some operators will block this by allowing the phone to use only a single SIM, or only a SIM issued by them; this practice is known as SIM locking, and is illegal in some countries.


If it is required that performing a task or service requires timely response of control functionality to inputs or measurements, there is a deadline for the delivery of the service. The automation controllers must not only perform a specific functionality, they must do so within deadlines defined by the specific application, measured by the flow of time. This is usually the case when controlling parts of a physical entity (like a car). A system is considered a real-time system: when must perform specific services within specific deadlines. It is important to note that real time performance does not mean fast performance. A system could be slow but still real time. (e.g. A bell rings each hour sharp without any delay. Because the service of ringing is performed each hour on time without delays and deterministically the bell is considered real time system).

A real time system could be SOFT REAL TIME SYSTEM (when meet the deadlines with high probability) or HARD REAL TIME SYSTEM (when always meet the deadlines on time).

A real time system that performs at least one safety critical function it is called a SAFETY CRITICAL REAL TIME SYSTEM. In real time systems with safety critical functions, timeliness and predictability of the services are essential. Safety critical real time systems  usually have (some) hard deadlines.