Voice API Programming Guide — June 2005 123
Send and Receive FSK Data
10.3 ADSI Operation
ADSI data is encoded using a standard 1200 baud modem specification and transmitted to the
telephone on the voice channel. The voice is muted for the data transfer to occur. Responses from
the ADSI telephone are mapped into DTMF sequences.
ADSI data is sent to the ADSI telephone in a message burst corresponding to a single transmission.
Each message burst or transmission can contain up to 5 messages, with each message consisting of
one or more ADSI commands.
The ADSI alert tone causes the ADSI telephone to switch to data mode for 1 message burst or
transmission. When the transmission is complete, the ADSI phone will revert to voice mode unless
the transmission contained a message with the “Switch to Data” command.
After the data is transmitted, the ADSI telephone sends an acknowledgment consisting of a DTMF
“d” plus a digit from 1 to 5 indicating the number of messages in the transmission that the ADSI
telephone received and understood. By obtaining this message count and comparing it with the
number of messages transmitted, you can check for errors and retransmit any messages not
received. (If you send 4 messages and the telephone receives 2, you must resend messages 3 and 4.)
You can send more than one transmission during a call. After the initial transmission of a call, you
do not have to re-establish the handshaking (sending the alert tone or receiving the
acknowledgment digit) as long as you have left the ADSI telephone in data mode using the ADSI
“Switch to Data” command. This is useful for performing additional data transmissions during the
same call without needing to send the alert tone or receive the acknowledgment digit for each
transmission.
10.4 One-Way ADSI
One-way ADSI support enables Intel telecom boards to be used as ADSI servers and to support
ADSI features such as visual voice mail. One-way ADSI allows for the one-way transmission of
data from a server to a customer premises equipment (CPE) device, such as a display-based
telephone. The phone (CPE) sends dual tone multi-frequency (DTMF) messages to the server,
indicating whether the data was received successfully.
For a more detailed description of the one-way ADSI data transfer process, see Section10.8,
“Developing ADSI Applications”, on page127.
ADSI data can be transferred only to display-based telephones that are ADSI compliant. Check
with your telephone manufacturer to find out if your telephone is a true ADSI-compliant device.
An ADSI alert tone, referred to as a CAS (CPE Alerting Signal), is sent by the server to query a
CPE device, such as an ADSI display phone. The device responds appropriately and, if the device
is ADSI-compliant, the ADSI data transfer is initiated.
Note: ADSI-compliant phones are also referred to as "Type 3 CPE Devices" by Telcordia Technologies
and by the Electronic Industry Association/Telecommunications Industry Association (EIA/TIA).