SMS Network Architecture and Internal Protocols
In the SMS network
operated by GSM service providers four layers of transport are used (Figure
1.):
SM-AL (Application Layer)
SM-TL (Transfer Layer)
SM-RL (Relay
Layer)
SM-LL (Lower Layers)
Ozeki NG - SMS Gateway is located in the
SM-AL layer. When sending an SMS message, the software creates protocol data
units (PDUs) transported by the SM-TL layer. When a GSM device attached to the
PC receives an SMS message, the message is also encoded according to
the SM-TL layer PDU
specification. Ozeki NG - SMS Gateway decodes this PDU and makes the message
readable for computer programs and computer users.
Figure 1 - SMS network layers
To
understand how the SMS travels from the mobile phone to the SMSC, look
at Figure 2 below. In this figure you can see which protocols are used and which
GSM network entities take place in the communication process. As you can see,
the mobile phone (Mobile station) transmits the SMS message to the GSM base
station (BTS) through a wireless link. Then the message goes though the
backbone network of the service provider. The Mobile Switching Center
(MSC), the Home Location Register (HLR) and, optionally, the Visitor Location
Register (VLR) is used to find out the appropriate Short Message Service
Center (SMSC) which will store and forward the message when the receiving party
becomes available.
Figure 2 - SMS transportation
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