Software for Telecoms & Audio
Call Waiting Caller ID (Standard) Detector DSP C Code
Description: implements the landline telephony function of Call Waiting Caller IDentity (CWCID) generation. CWCID is sent off-hook in an established call to pass the identity of a third party trying to call one of the talking parties. The talking party can then accept the call by a hook-flash. CWCID is signalled from the exchange - the Generator end - by an alerting dual-tone signal CAS, and acknowledged by the subscriber - the Detector end - with another dual-tone signal ACK. The Caller ID message bytes are then sent by V.23 or Bell 202 modem modulation, formatted as in on-hook Caller ID. The CWCID Detector is for "standard" locales - eg ETSI, UK SIN 227, US Bellcore SDMF/MDMF, Bell Canada - but not for Japan. The software function summary is:
CWCID Detector: on detecting CAS it sends ACK, then demodulates the Caller ID data verified against the checksum, using the on-hook CID decoder routine. The Detector returns diagnostics, signalling CAS-detected for voice-blocking, then full message reception, or else failure due eg a CRC error.
The Detector forms
a buffer of the complete message data for the user interface in parameterised
byte form, excluding the checksum byte. Message de-parameterisation in
the user code gives flexibility in dealing with Caller ID categories.
The message buffer format is 2 per 16-bit word for efficiency in multi-channel
data receiver performance:
#example figures from compiling for the TI TMS320C5000(C55x) DSP processor
at 8.0kHz sampling
Availability: NOW - sale is under licence - integration support offered