Guard tone
Encyclopedia
Guard tone is a feature of wireline modem
s.
The guard tone is sent by the answering modem after it has sent the answer tone
. It is a single continuous tone with a frequency of either 1800 Hz or 550 Hz, sent at a level of -6dB or -3dB, respectively, below the level of the transmitted data signal power.
It is used with V.22 and V.22bis modulation modes to prevent the high-band data signal from interfering with the operation of billing apparatus in certain countries where in-band signalling was commonplace in the 20th century.
1800 Hz is used in the UK and some Commonwealth countries, while 550 Hz is used in some Scandinavian countries. Guard tones are not used in North America.
The guard tone is controlled by the &G AT command of the Hayes command set
.
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
s.
The guard tone is sent by the answering modem after it has sent the answer tone
Answer tone
Answer tone is a feature of wireline modems.The answer tone is the first signal sent by the answering modem after the billing delay. In its most basic form, it is a single continuous tone with a frequency of 2100 Hz ....
. It is a single continuous tone with a frequency of either 1800 Hz or 550 Hz, sent at a level of -6dB or -3dB, respectively, below the level of the transmitted data signal power.
It is used with V.22 and V.22bis modulation modes to prevent the high-band data signal from interfering with the operation of billing apparatus in certain countries where in-band signalling was commonplace in the 20th century.
1800 Hz is used in the UK and some Commonwealth countries, while 550 Hz is used in some Scandinavian countries. Guard tones are not used in North America.
The guard tone is controlled by the &G AT command of the Hayes command set
Hayes command set
The Hayes command set is a specific command-language originally developed for the Hayes Smartmodem 300 baud modem in 1981. The command set consists of a series of short text strings which combine together to produce complete commands for operations such as dialing, hanging up, and changing the...
.