THE PROCESS BEHIND SENDING AN SMS (GSM)

THE PROCESS BEHIND SENDING AN SMS (GSM)

 Have you ever wondered what happens when you send a text? For it to reach its final destination, it passes through series of protocols and validation in the service provider’s systems. This systems includes base transceiver stations (BTS), base switching center (BSC), mobile switching center (MSC) and the database systems (ELR, VLR, EIR)

When an message is immediately sent, it is transmitted via the radio waves in the air to the BTS, then to the BSC via the ABIS channel. The BSC function is to control traffic and to assign signals from one channel to the other. As our message leaves the BSC, it is transferred to the MSC and then stored in the within SMSC (short message service center)  while the subscribers details are validated using the following database.

·         Home Location Register (HLR) - Main copy of the database

·         Visitor’s location Register (VLR - The copy of the HLR

·         Equipment Identification Register (EIR) – checks mobile devices ownership and information i.e. stolen or cloned.

This database ELR and VLR contains the following

·         IMSI (International mobile subscriber’s identity) which has

Ø  Country code

Ø  Callers ID

Ø  Mobiles phones unique ID (EMEI)

·         MSISDN (Mobile subscribers ISDN number) which has

Ø  Your mobile number

Ø  Subscriber’s mobile phones tariff. I.e. Texts, Minutes and data.

The channel between the BSC and the MSC is referred to as the “A” interface .The MSC handles significant tasks and this makes it the Heart of the communication channel.

Once this information has been confirmed our message can move to the final part of the journey. At this point the MSC asks the HLR for the recipient location using the phone number saved in the massage. 

 

Once this information has been received the message is released and passed through the transit channel to the appropriate MSC which then passes it to the BTS in the geographical range of the recipient.

 

Finally the message reaches its destination.

BY: KEN RONOH.