SMS Basics and Types of SMS

This Article on SMS covers following:
SMS basics and types
SMS network and elements
SMS MO MT call flow
SMS versus MMS

Everyone is aware of voice communication from one mobile to the other mobile and from landline phone to the other mobile/phone. Text based communication is slowly replacing the voice communication as it is very cheaper. When person just want to send short information to some one they do not call and just sends the message to the opposite person. This is referred as SMS or short message service. But the difference between voice and SMS is that voice is realtime and SMS is non-realtime.

SMS is about 160 characters maximum in size. It comes to about 140 bytes in GSM wherein each character is coded with 7 bits.

As mentioned SMS is non-realtime service means SMS sent from one mobile to the other gets stored on SMSC and computers before being delivered. It is also referred as store and forward service. For details of SMS path from originating mobile to the terminating mobile refer our page on SMS MO/MT call flow.

SMS can be transported using signaling channel(i.e.SDCCH in GSM) when GPRS is not activated. If GPRS is activated it can be carried on traffic channel too. As SMS is carried by signaling channel it can be sent while the voice or data communication is in progress. As for voice and data communication TCH or traffic channels are used.

SMS Working

The figure-1 depicts working of SMS. As shown user#1 transmits SMS (meant for user#2) which goes to SMS gateway. SMS gateway forwards the same to mobile service provider which retransmits the same SMS to user#2.

SMS Types

Depending upon the application and the way SMS is sent from originating system to the terminating system it is classified into P2P,A2P,P2N and I2P categories.The same is described below.

Person to Person(P2P): This type of SMS is sent and received between two mobile subscribers. If SMS is within the same RAT(i.e. say GSM to GSM) then originating and terminating SMSC is same. But if SMS is within two different RATs then originating SMSC sends the message to corresponding destination SMSC of terminating RAT.

Application/Advertiser to Person(A2P): In this type of SMS adverising agencies reach out to the service operator to send their ad. details to the mobile subscribers registered with them. With this ad. detail service operator broadcasts SMSs to the mobiles. This method is also referred as push mode.

Person to Network(P2N) or person to application(P2A): In this type of SMS, content provider will provide details such as ringtones,games,pictures to be downloaded to the network service operator/provider. They both will have agreement and accordingly will be charged. In this type, service provider gives out short codes to the content provider.

Internet to Person(I2P): In this type of SMS, few websites allow net users to send SMS to the mobile subscribers from the internet. Few websites also accept incoming messages from the mobile subscribers.

Useful Links

GSM RF planning  Mobile Terminated Call  GSM downlink PS data call flow  GSM uplink PS data call flow  GSM Tutorial   GSM protocol stack   GSM physical layer   GPRS protocol stack   GPRS tutorial   CS vs PS 


RF and Wireless Terminologies