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Operation

When a user sends a text message (SMS message) to another user, the phone actually sends the message to the SMSC. The SMSC stores the message and then delivers it to the destination user when they are available. This is a store and forward operation. The SMSC usually has a configurable time limit for how long it will store the message, and users can usually specify a shorter time limit if they want.

Protocols

For bulk transmission and reception of SMS messages, SMSCs have conventional, fixed, network interfaces as well as mobile network interfaces. A number of protocols have been defined to support this sort of wire-line access:

• SMPP (Short message peer-to-peer)
  • The most common protocol and the only non-proprietary one in wide use.
• EMI/UCP (External Machine Interface/Universal Computer Protocol)
  • A proprietary protocol by market leader LogicaCMG.
• CIMD (Computer Interface to Message Distribution)
  • A proprietary protocol developed by Nokia for its Artuse SMSC.
• OIS (Open Interface Specification)
  • Despite the name, a proprietary protocol developed by Sema Group (now Airwide Solutions).

Companies

Two companies who make many of the SMSCs in use in the GSM world are Logica and CMG - or rather just one company, LogicaCMG, as these two merged on January 1st, 2003. Other large players include Comverse Technology, Nokia, Huawei, Unisys, Airwide Solutions, Jinny, Oksijen, Telesoft, Lucent and Motorola.