SMS traffic is doubling in every two years. Operators used to see this as a new revenue source. Many companies started offering services around SMS. But this explosive growth of  SMS has started to created problems, mainly a degradation of the voice services.

Every operators are facing service problems during holidays and festival seasons just because of the large volume of SMS messages that are being sent. During New year almost every network will be jammed from 11:45 to 12:15. Every subsriber will be busy. This is not because everyone is calling up each other, but because the SMS traffic is blocking the voice services.

GSM networks use control channels and voice channels for handling calls and SMS messages. The control channel is used to handle SMS messages and also to setup calls. Once the call setup is finished the call proceeds using the voice channel.

Control channels have far lesser bandwidth than voice channels.

When lots of messages are pushed into the network the control channels will become busy and no control channel will be available for call setup. So all the voice services fail.

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BSNL Calcutta recently introduced Voice SMS services for its Landline, WLL and GSM customers.

To access the service dial 1256 from your phone and wait for the IVR. Follow the instructions to record the message and input recipient numbers.

The service currently supports 45 seconds of voice in a single message

If the called party is busy 15 attempts will be made to deliver the message before the message is discarded.

Group messaging facility is also available which will help you to send the same voice message to a group of numbers. Its really useful when sending festival greetings and similar applications.

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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 couldnt find much information about it.

Then again another article in Elektor about a project to control electrical appliances by sending an SMS. This happened in S3, and I found that a friend and a senior of mine named Robin was planning to do this as his project. I followed the project with him and learned a lot from it.

Now It was time for us to do a project. We decided we will do something with SMS and mobile phones. The team mates were Me, Sanil, Robin, …………… The project was to create an application that will fetch the phone number of every student in our class if we send in his roll number. If you send 26 (My roll number) to a particular number (984724972. Haris number used for testing) you will get 04829243366 (My home number) as a return message.

Learning to use serial ports, AT commands, solving timing issues, the project took almost 6 months to complete. We did the project in C++. That was the first real successful experiment with SMS. After that we did the same stuff in java, found out some easy to use serial APIs and SMS engines.

Then after one year the SMS thing came up again, but this time it was for our juniors, It was time for them to do a project and we thought we could make some money helping them to do their project. We helped a team, develop a SMS spamming application in Java. That was selected as the best project for that year. One of the team members Jinson, is still with me.

Now we all were in the final semester and it was time for us to do our final year project. We were planning to do a driver in linux for mobile phones that supported the standard AT command set. We couldnt find anyone to help us with a driver, so we dropped that project and did a software router for our final year project.

After college we joined for a course in programming handhelds and the company was trying to develop SMS applications for the railways. Our knowledge and experience paid off and we successfully developed an SMS alerting application for Indian Railways using a GSM modem. During that period we played with GSM modems a lot and developed many SMS applications for data fetching, alerting etc. We even did a game that can be played by sending SMS. (Credits for coding goes to Lakshmi).

It was during this period that we came to know about SMS gateways and short codes. I tried to get hold of one, but didnt succeed. Exactly at that point we found out some guys who had access to all the resources that we were looking for, the rest is history.

Products began to roll out. FastAlerts desktop version, Short Code backend, www.go3636.com , SMS CRM tool, Campaign Manager, FastAlerts Web Version, and some minor J2me applications and customized SMS tools for some clients.

Recent additions to the SMS basket are a multilingual online keyboard which can be used to send SMS in almost every language in the world, Application specific SMS from J2me, and GSM modem based SMSC for testing purposes.

The future plans are the setup an our own SMSC and expand FastAlerts to all countries.

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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 where the destination mobile is and forwards the message to the destination MSC if the destination mobile is available. If the mobile is not available the message gets stored in the current SMSC itself. In most installations If a mobile is not available for SMS delivery the SMSC will not retry. Instead the destination MSC will inform the SMSC when the mobile comes back in range.

SMS handling is a store and forward operation unlike USSD.

SMS has got a validity period, for which it will wait for the destination mobile to the available. After that time the SMSC will delete the message.  The validity period can be set by the user. Normal validity is 1 day.

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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 regularly are

• Alerts About special offers, services and news
• Balance enquiry
• Changing tariff plan and subscribing to various VAS services.
• Recharging using prepaid vouchers

Other than these many interesting services can be given using the USSD platform. One such service is the “call back” service. The user will use USSD to send a USSD message to his friend asking him to call back. This is done by pressing the USSD service number and the number to which the alert needs to be send. Assume 14 is the service number and you want me to call you back. Press this on your mobile and press dial.

*14*9846831128#

I will receive a message, “XXXXXXXXXX wants you to call him back” where XXXXXXXXXX will be your number.

USSD supports interactive sessions where a service can be provided by using a menu. Micro payment market gets a real boom with the USSD technology in place. Users can transfer money from their mobile prepaid and post paid account to other mobile accounts. There will be a service number associated with it. When the user presses the number and dials, he will be presented with menus where he has to enter the amount and the mobile number to which the money needs to be transferred.

USSD is a session oriented technology and hence it supports menus and transactions. The state of the interaction between the user is tracked by the USSD server. Response times for USSD messages are shorter than SMS because SMS is a store and forward technology. All USSD services are accessed by dialing numbers between * and #. The handset recognizes those numbers and forwards the request to the USSD server instead of initializing a normal call or a data call. No additional application, phone menu or sim menu is needed for USSD to function as USSD is supported by every GSM handset.

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