> 2.1 | Overview

> Your GSM engine offers basic support for equipment using CTM standards. Text characters typed on a TTY device can be transformed into special audio burst signals for reliable transmission via the existing speech channels of a cellular phone system. During typing, the message is sent over the GSM network. The text telephone characters are transformed into audio signals. At the receiving end, the CTM signal is detected and decoded by the corresponding functions of the CTM receiver. The decoded characters are available at the CTM receiver’s output.
> If neither the CTM demodulator nor the CTM transmitter detect a CTM signal, the incoming signal is forwarded to the output of the CTM modem in order to support alternating between text and voice.
> To use a TTY device the CTM can be:

> • | already implemented into your device

> • | a separate unit

> • | supported by the host application firmware (please note that Siemens wireless modules do not support this solution)

> Figure 1: Reference configuration to support TTY communication