Short Message Transfer

Overview

The SM-TE connects to the network using the PSTN as access. The SM-SC connects to the network via an ISDN primary rate interface, SS7 or other connection type.

To send and receive Short Message (SM) transfers, a voice-band communication path must be established in the PSTN between the SM-TEs and SM-SC using basic call control procedures.

The SM transfer is divided into two phases:

• SM submission - transfer of a SM from the SM-TE (sender) to the SM-SC.

• SM delivery - transfer of a SM from the SM-SC to the SM-TE (receiver).

Figure 7-7 Short Message Transfer

Short Message Submission

In the SM submission phase, the SM-TE establishes a a voice-band communication path to the SM-SC in order to submit the SM.

After the voice-band connection between SM-TE and SM-SC has been established, the end-to-end SM data transfer phase is entered for Short Message transfer from SM-TE to SM-SC.

When this occurs, the Caller ID (calling line identification) of the SM-TE is routed to the SM-SC. The SM-SC uses this information to identify the SM-TE and for billing purposes. After the SM has been transferred, the connection between SM-TE and SM-SC is released.

SMS Submission from SM-TE to SM-SC

After the SM-TE originates the call and the SM-SC answers it, the connection is ready for the SM transfer between SM-TE and SM-SC.

The SM-SC then initiates the data transfer by sending the appropriate Data Link Layer message DLL_SMS_EST. The Data Link Layer in SM-TE then sends the DLL_SMS_DATA message containing the SMS information. The SM-TE then releases the connection by sending the DLL_SMS_REL message.

Short Message Delivery

In the SM delivery phase, the SM-SC establishes a call to the SM-TE to deliver the SM to the SM-TE. In this case, the network provides the Caller ID (calling line identification) of the SM-SC to the SM-TE. The SM-TE uses this Caller ID information to identify and connect an incoming call from the SM-SC automatically.

As in the SM submission phase, the SM is transmitted from the SM-SC to the SM-TE after the voice band connection between SM-SC and SM-TE has been established. After the SM has been transferred, the connection between SM-SC and SM-TE is released.

SMS Delivery from SM-SC to SM-TE

To deliver a SM to the designated SM-TE, the SM-SC calls the SM-TE's subscriber line.

Depending on the delivery mode identifier in the calling party number of the SM-SC when calling SM-TE’s subscriber line, the following two options are available:

• The SM-TE answers the call and receives the SM.

• The SM-SC terminates the call after a short time after transmitting the SM-SC's Caller ID to the SM-TE. The SM-TE then generates a call back to the SM-SC to receive the SM.