The SMS network entities

SMS messages are created by mobile phones or other devices (e.g.: personal computers). These devices can send and receive SMS messages by communicating with the GSM network. All of these devices have at least one MSISDN number. They are called Short Messaging Entities. To understand their role in the GSM SMS network please take a look at the following figure:

Figure 1 - Short Messaging Entities (SME) in the GSM network

The SME-s are the starting points (the source) and the end points (the receiver) for SMS messages. They always communicate with a Short Message Service Center (SMSC) and never communicate directly with each other. An SME can be a Mobile telephone. Depending on the role of the mobile phone in the communication, we can talk about two kinds of SMS messages: Mobile Originated (MO) messages and Mobile Terminated (MT) messages. MO messages are sent by the mobile phone to the SMSC. Mobile terminated messages are received by the mobile phone. The two messages are encoded differently during transmission.

An SME can also be computer equipped with a messaging software, such as the Ozeki Message Server, that can communicate directly with the SMSC of the service provider. For this communication a mobile-phone-sms.gif with a phone-to-pc data cable or a direct IP link can be used.

send sms with a mobilephone
Figure 2 - Ozeki Message Server use a mobilephone to send and receive sms

direct IP SMS connection
Figure 3 - Ozeki Message Server using direct IP SMS connection

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