The first time I send an SMS was long back, when they introduced mobile phones in Palai. I was a still a school kid and my cousin had a mobile, a big one and I send an SMS from it. It was a nice experience, but at that time SMS cost something like 5Rs per message. Then while in college I saw an article in Elektor about a GSM module which can be used to send and receive SMS without a mobile phone. Did some googling about it but...

Finally the picture is mine. Took me 30 mins. BTS – Base Transceiver Station (Antenna) BSC – Base Station Controller MSC – Mobile Switching center HLR- Home Location Register VLR – Visitor Location Register SMSC – Short Message Service Center When a user sends an SMS, the request is placed via the MSC. The MSC forwards the SMS to the SMSC where it gets stored. The SMSC queries the HLR to find out...

Unstructured Supplementary Services Data (USSD) is a GSM service that allows high speed interactive communication between the subscribers and applications across a GSM Network. A sample USSD service is the bill status service accessed by dialing *141# or similar numbers in between * and #. USSD applications can be thought of as an IVRS (Interactive Voice Response System) with out voice. Some of the USSD applications that we use...

PSTN – Public Switched Telephone Network GMSC – Gateway MSC MSC – Mobile Switching Center BSC – Base Station Controller BTS – Base Transceiver Station MSCs are the telephone exchanges of GSM networks. They route the calls based on the destination numbers current location. The BSCs and BTS are responsible to taking the call from the MSC to the handset. Those two components together handle the complications...

Once again apologies for using somebody else’s image. POTS – Plain Old Telephone System MSC – Mobile Switching Center BSS – Base Station SubSystem HLR – Home Location Register VLR – Visitor Location Register From our land line we dial a mobile number. Our telephone exchange identifies that its a mobile number and its of a particular operator. The call is routed to that operators Gateway MSC....

This is the basic unit of a GSM network. The image is not mine, I copied it from a PDF I got from the internet. The most important part of the network is the MSC or the Mobile Switching Center. MSC is equivalent to the telephone exchange. It has got necessary switching equipment to route a call to the appropriate MSC or external switching device, PSTN or PSPDN. PSTN – Public Switched Telephone network (our ordinary telephone...