1. SMS

2. Mobile Computing over SMS
GSM is digitized but not packetized. A circuit is established and the user is charged based on the time the circuit is active and not on the number of packets transacted.
GPRS also known as 2.5G, which is the next phase within the evolution of GSM, supports data over packets.
WAP is a data service supported by GPRS and GSM to access Internet and remote data services.
A unique data service of GSM, not found in older analog systems, is the Short Message Service (SMS). SMS enables sending and receiving text messages, and form, GSM mobile phones.

3. SMS & it’s Strengths
Now a days SMS is the most popular data service within GSM, for SMS SS#7 signaling channels are always physically present but mostly not active. When during an active user connection or in the idle state.
SMS uses the free capacity of the signaling channel, each short message is up to 160 characters.
Omnibus nature of SMS:- SMS uses SS7 signaling channel, only a service that allow a subscriber to send a long distance SMS without having long distance subscription. For international call user have to activate international calling facility, but for SMS need not to activate international SMS facility.
Asynchronous:- there is a request and response pair making it synchronous at the transaction level. SMS can be used as a transport bearer for both synchronous and asynchronous information exchange.
Stateless:- SMS is session less and stateless. SMS is the best bearer for notifications, alerts and paging.
Always connected:- SMS used SS7 signaling channel for data traffic, the bearer media is always on. User can’t switch off or divert any SMS.

4. SMS Architecture There are two types for SMS,
1) SMMT – Short Message Mobile Terminated
SMMT is an incoming message from the network side and
terminated in the MS.
2) SMMO – Short Message Mobile Originated
SMMO is an outgoing message, originated in the user device and
forwarded to the network for delivery.
SMS network structure

5. For outgoing message, the path is from MS to SC via the VLR and the IWMSC function of the serving MSC, now for incoming message the path is form SC to the MS via HLR and the GMSC function.
SMS bearer using for Information exchange, Origin server or the Enterprise server needs to be connected to the SC through a short message entity (SME).
SME is works as a SMS gateway.

6. SMMT:- basic purpose for the message is sent from SC to the MS, it’s done in one transaction. SC of the serving network is never used during the delivery of MT or incoming message. SMS can be sent from any SC in any network to a GSM phone, SMMT message mobile operation independent.
SMMO:- It’s outgoing message originated in the MS. MSC forwards the message to the home SC. In SS7 terminology SC is a SCP (Service Control Point). Message is sent from the home SC to the MS as a MT message.

7. Value Added Services Through SMS
It’s a additional service offering but user have to pay for it.
Sometimes stand-alone operationally.
Can be an add-on to basic service, and as such
VAS over SMS are entertainment and information on demand. Information on demand has three categories.
Static Information:- this information is not change frequently, e.g. bus timetable, restaurant menu.
Dynamic Information:- information changes once in a day. e.g. daily horoscope.
Real-time information:- information change a continually, e.g. stocks, live cricket score.
Some another examples for VAS…
News/Stock quotes service
Session-based chat application
through SMS
Health care services
Micro-payment services