130 Voice API Programming Guide — June 2005
Send and Receive FSK Data
10.8.3 Technical Overview of Two-Way ADSI Data Transfer
In two-way ADSI data transfer, both the ADSI server and CPE device can transmit and receive
ADSI data messages. The CAS is used to initiate the transfer of ADSI FSK data and to return the
CPE to voice mode after the data exchange is completed.
The transactions that occur between the server and the CPE in two-way ADSI data transfer are as
follows:
1. The server initiates the data transfer by sending a CPE Alerting Signal (CAS) to the CPE
equipment.
2. Upon receipt of the CAS, the CPE device generates an ACK (DTMF ‘A’ signal) to the server.
At this point the CPE device has switched from voice mode to data mode. (Once the CPE
device is in data mode, subsequent FSK data transmissions do not require the CAS.)
Note: Only ADSI-compliant CPE devices will respond to the CAS sent by the server. Check
with your manufacturer to verify that your CPE device is a true ADSI-compliant
device. ADSI-compliant devices are also referred to as "Type 3 CPE Devices" by
Telcordia Technologies.
3. When the ACK signal is received, the server initiates the FSK transmission sequence. Each
FSK transmission sequence can contain anywhere from 1 to 5 messages. A "Switch to
Peripheral Mode" message (using 0x0A as a ‘requested peripheral’ code) must be included
within the FSK transmission sequence.
4. The CPE receives the FSK data and uses the checksum included within the sequence to
determine the number of messages successfully received.
5. The CPE device then responds to the server with a DTMF ‘D’ followed by a DTMF ‘0’
through ‘5’ to indicate the number of messages successfully received. In addition, the CPE
device acknowledges the "Switch to Peripheral Mode" message by responding with either
•DTMF ‘B,’ indicating that the requested peripheral is available and on line
•DTMF ‘A,’ indicating that the requested peripheral is not available
6. The server interprets the DTMF signals as follows:
•‘D’ followed by a DTMF in the range of 1 – 5 = ACK
•‘D’ followed by a DTMF ‘0’ = NAK
•DTMF ‘B’ = requested peripheral available (ready to receive and transmit ADSI data)
•DTMF ‘A’ = requested peripheral unavailable (unable to transmit or receive ADSI data)
Once the CPE device has acknowledged the "Switch to Peripheral Mode" message, the CPE may
transmit data to the server at any time. The server must be prepared to receive data at any time until
the CPE peripheral is switched back to voice mode. To return the CPE peripheral to voice mode,
the server sends a CAS to the CPE. Upon receipt of the CAS, the CPE responds with a DTMF ‘A’
signal. Receipt of DTMF ‘A’ at the server completes the return to voice mode transition.