RFX144V24-S23 and RFX96V24-S23 Modem Designer’s Guide
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10-1
10. CALLER ID
10.1 INTRODUCTION
Calling Number Delivery (CND), better known as Caller ID, is a telephone service intended for residential and small business
customers. It allows the called Customer Premises Equipment (CPE) to receive a calling party's directory number and the
date and time of the call during the first silent interval in the ringing cycle. The customer must contact a Bellcore Client
Company to initiate CND service.
10.2 CALLING NUMBER DELIVERY SPECIFICATION
All of this CND information, according to Bellcore, is sent between the first and the second ring and starts as early as 300 ms
after the first ring burst and ends at least 475 ms before the second ring burst.
The following information summarizes the CND information provided by Bellcore.
10.3 PARAMETERS
The data signaling interface has the following characteristics:
Link Type: .....................2-wire, simplex
Transmission Scheme: ..Analog, phase-coherent FSK
Logical 1 (mark): ...........1200±12 Hz
Logical 0 (space):..........2200±22 Hz
Transmission Rate: .......1200 bps
Transmission Level: ......-13.5±1 dBm into 900
Ω
load
10.4 PROTOCOL
The protocol uses 8-bit data words (bytes), each bounded by a start bit and a stop bit. The CND message uses the Single
Data Message format shown below.
Channel
Seizure Signal
Carrier Signal
Message Type
Word
Message
Length Word
Data Word(s)
Checksum
Word
Channel Seizure Signal
The channel seizure signal is 30 continuous bytes of 55h (01010101). This provides a detectable alternating function to the
modem.
Carrier Signal
The carrier signal consists of 130±25 ms of mark (1200 Hz) to condition the receiver for data.
Message Type Word
The message type word indicates the service and capability associated with the data message. The message type word for
CND service is 04h (00000100).
Message Length Word
The message length word specifies the total number of data words to follow.
Data Words
The data words are encoded in ASCII and represent the following information:
• The first two words represent the month.
• The next two words represent the day of the month.
• The next two words represent the hour in local military time.
• The next two words represent the minute after the hour.
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