Siemens AC75 Benutzerhandbuch

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AC75_ATC_V01.002

Page 476 of 569

10/30/06

Confidential / Released

AC75 offers basic support for equipment using the CTM standard (Cellular Text Telephone Modems). The ben-

efit of CTM is that text characters typed on a TTY device (Text Telephone Type-writer) can be transformed into

special audio burst signals for reliable transmission via the existing speech channels of a cellular phone system.

If CTM mode is activated, the ME will set the necessary bearer capability bit on outgoing (mobile originated) calls

and incoming calls with this bearer capability bit set are accepted. The TE needs to decode the special audio

burst signals. 

If CTM mode is disabled, the ME will clear the bearer capability bit on mobile originated calls and incoming calls

with the bearer capability bit set are rejected because the AC75 expects that CTM coded speech data cannot be

decoded by the TE. 

Designed to set the module's speech system into CTM mode, the 

 command allows a CTM device

to be connected to one of the three audio interfaces of AC75. Traditional TTY devices that do not incorporate

CTM functionality can be connected through an external TTY-to-CTM adapter. 

Related documents: Refer to the relevant standards, such as 3GPP TS 26.226 (ETSI TS 126 226) and 3GPP

TS 23.228 (ETSI TS 123 226). 3GPP documentation can be retrieved, for example, from http://www.3gpp.org/

specs/specs.htm. Application Note 22 "Using TTY/CTM equipment" supplies information needed to connect

TTY/CTM equipment to the AC75. 

Requirements for using TTY/CTM features:
• TTY/CTM functionality requires audio mode 5 or 6 with all audio parameters set to their factory default.

To do so, first enter the 

 command to select audio mode 5, then use 

 and 

 to

restore the default values. Alternatively, factory defaults of all audio parameters in audio modes 2 - 6 can eas-

ily be set with 

.

• Depending on which audio interface the CTM device is connected to select the according settings via

. 

0

(P)

Audio path is in normal speech mode.

1

Audio path is in TTY/CTM mode.

Test Command

AT^SNFTTY=?

Response(s)

^SNFTTY: 

(list of supported 

s) 

OK

Read Command

AT^SNFTTY?

Response(s)

OK

Write Command

Response(s)

OK 

ERROR 

Reference(s)

PIN

ASC0 ASC1 USB MUX1 MUX2 MUX3 Charge

4

Last

SIEMENS

<audioState>

(num)