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Guard Tone
Guard tone is a feature of wireline modems. 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 AT command of the Hayes command set. North American Bell 103-style modems (300 bit/s) were incompatible with UK in-band signalling (the modem tones would disconnect the call) unless a guard tone is provided. Most of these (now-obsolete) modems did not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modem
A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulation methods, modulating one or more carrier wave signals to encode digital information, while the receiver Demodulation, demodulates the signal to recreate the original digital information. The goal is to produce a Signal (electronics), signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio. Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines. These generally operated at 110 or 300 bits per second (bit/s), and the connection between devices was normally manual, using an attached telephone handset. By the 1970s, higher speeds of 1,200 and 2,400 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 (or 2225 Hz for Bell modes). It is the tone heard by the caller after dialing the number. The plain 2100 Hz tone is meant to disable echo suppressors on international trunk connections. It may include 180° phase reversals at intervals of 450 ms to disable network echo cancellers. It may also be amplitude modulated by a 15 Hz signal to indicate ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ... V.8 capability. References * * {{DEFAULTSORT:Answer Tone Modems ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hayes Command Set
The Hayes command set (also known as the AT command set) is a specific command language originally developed by Dennis Hayes for the Hayes Smartmodem 300 baud modem in 1981. The command set consists of a series of short text strings which can be combined to produce commands for operations such as dialing, hanging up, and changing the parameters of the connection. The vast majority of dial-up modems use the Hayes command set in numerous variations. The command set covered only those operations supported by the earliest 300 bit/s modems. When new commands were required to control additional functionality in higher speed modems, a variety of one-off standards emerged from each of the major vendors. These continued to share the basic command structure and syntax, but added any number of new commands using some sort of prefix character – & for Hayes and USR, and \ for Microcom, for instance. Many of these were re-standardized on the Hayes extensions after the introduction of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bell 103
The Bell 103 modem or Bell 103 dataset was the second commercial modem for computers, released by AT&T Corporation in 1962. It allowed digital data to be transmitted over regular unconditioned telephone lines at a speed of 300 bits per second. It followed the introduction of the 110 baud Bell 101 dataset in 1958. The Bell 103 modem used audio frequency-shift keying to encode data. Different pairs of audio frequencies were used by each station: * The originating station used a mark tone of 1,270 Hz and a space tone of 1,070 Hz. * The answering station used a mark tone of 2,225 Hz and a space tone of 2,025 Hz. Although original Bell 103 modems are no longer in common use, this encoding scheme is referred to generically as "Bell 103 modulation", and any device employing it as "Bell 103-compatible" or "a Bell 103 modem". For many years, higher-speed modems retained the ability to emulate the Bell 103, allowing a fallback method for data to be communicated at low sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
In-band Signaling
In telecommunications, in-band signaling is the sending of control information within the same band or channel used for data such as voice or video. This is in contrast to out-of-band signaling which is sent over a different channel, or even over a separate network. In-band signals may often be heard by telephony participants, while out-of-band signals are inaccessible to the user. The term is also used more generally, for example of computer data files that include both literal data, and metadata and/or instructions for how to process the literal data. Telephony When dialing from a land-line telephone, the telephone number is encoded and transmitted across the telephone line in form of dual-tone multi-frequency signaling (DTMF). The tones control the telephone system by instructing the telephone switch where to route the call. These control tones are sent over the same channel, the copper wire, and in the frequency range (300 Hz to 3.4 kHz) as the audio of the teleph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
McGraw-Hill Professional
McGraw Hill is an American educational publishing company and one of the "big three" educational publishers that publishes educational content, software, and services for pre-K through postgraduate education. The company also publishes reference and trade publications for the medical, business, and engineering professions. McGraw Hill operates in 28 countries, has about 4,000 employees globally, and offers products and services to about 140 countries in about 60 languages. Formerly a division of The McGraw Hill Companies (later renamed McGraw Hill Financial, now S&P Global), McGraw Hill Education was divested and acquired by Apollo Global Management in March 2013 for $2.4 billion in cash. McGraw Hill was sold in 2021 to Platinum Equity for $4.5 billion. Corporate History McGraw Hill was founded in 1888 when James H. McGraw, co-founder of the company, purchased the ''American Journal of Railway Appliances''. He continued to add further publications, eventually establishing The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modems
A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulation methods, modulating one or more carrier wave signals to encode digital information, while the receiver Demodulation, demodulates the signal to recreate the original digital information. The goal is to produce a Signal (electronics), signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio. Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines. These generally operated at 110 or 300 bits per second (bit/s), and the connection between devices was normally manual, using an attached telephone handset. By the 1970s, higher speeds of 1,200 and 2,400 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
