In telecommunications, in-band signaling is the sending of metadata and control information in the same band, on the same channel, as used for data. In Telecommunication, signalling (UK spelling or signaling (US spelling has the following meanings The use of signals for controlling communications Metadata ( meta data, or sometimes metainformation) is "data about data" of any sort in any media In Telecommunication, signalling (UK spelling or signaling (US spelling has the following meanings The use of signals for controlling communications
Contents |
Telephone
For example, when dialing a modern telephone, the telephone number is encoded and transmitted across the telephone line as Dual-Tone Multi-Frequency (DTMF) tones. Basic principle A traditional landline telephone system also known as "plain old telephone service" (POTS, commonly handles both signaling and audio information A telephone number or phone number is a sequence of numbers used to call from one Telephone line to another in a Telephone network. Dual-tone multi-frequency ( DTMF) signaling is used for Telephone signaling over the line in the voice-frequency band to the call switching center The tones "control" the telephone system by instructing the telephone company's equipment where to route the call to. In the field of Telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls These control tones are sent over the same channel and in the same band (300Hz to 3. Channel, in communications (sometimes called communications channel) refers to the medium used to convey Information from a 4kHz) as the voice and other sounds of the telephone call. In-band signalling is also used on older telephone carrier systems to provide inter-exchange information on how to route calls. IXC redirects here For the IATA airport codes see Chandigarh Airport For Interexchange Point see Internet Exchange Point Examples of this kind of in-band signalling system are SS5 and R2. CCITT5 was a Multi-frequency (MF telephone signalling system in use from the 1970s for International Direct Distance Dialing (IDDD R2 is a 1960s - and 1970s -era channel-associated-signalling Signalling protocol used outside of the former Bell System to convey information
Separating the control signals, also referred to as the control plane, from the data (if a bit-transparent connection is desired) is usually done by escaping the control instructions. In Telecommunications transparency can refer to The property of an entity that allows another entity to pass thorough it without altering either of the This article refers to codes used as commands for computing devices Occasionally, however, networks are designed so that data is (to a varying degree) garbled by the signaling. Allowing data to become garbled is usually acceptable when transmitting sounds between humans, since the users rarely notice the slight degradation, but this leads to problems when sending data that has very low error tolerance, such as information transmitted using a modem. Modem (from mo dulator- dem odulator is a device that modulates an analog carrier signal to encode Digital information
In-band signaling is insecure because it exposes control signals, protocols and management systems to the user(s), which may result in falsing. In Telecommunications, falsing describes a Decoder detecting a valid input when one is not present In the case of the blue boxes that were popular in the 1960s and 1970s, such falsing was deliberate. An early Phreaking tool the blue box is an electronic device that simulates a Telephone operator 's dialing console By using blue boxes to generate the appropriate tones, a caller could abuse functions intended for testing and administrative use to make free long-distance calls.
Modems may also interfere with in-band signaling, so in some countries, a guard tone is employed to prevent this. Guard tone is a feature of wireline Modems The guard tone is sent by the answering modem after it has sent the Answer tone.
Non telephone
As a method of in-band signalling, DTMF tones were also used by cable television broadcasters to indicate the start and stop times of local commercial insertion points during station breaks for the benefit of cable companies. See also Signalling (telecommunications In Telecommunications, in-band signaling is the sending of Metadata and control information in For the band see Broadcast (band Broadcasting is the distribution of audio and/or Video signals which transmit Until better, out-of-band signaling equipment was developed in the 1990s, fast, unacknowledged, and loud DTMF tone sequences could be heard during the commercial breaks of cable channels in the United States and elsewhere. Out-of-band is a technical term with different uses in Communications and Telecommunication.
These DTMF sequences were sent by the originating cable network's equipment at the uplink satellite facility, and were decoded by equipment at local cable companies. Uplink An uplink (UL or U/L is the portion of a communications link used for the transmission of signals from an Earth terminal A specific tone sequence indicated the exact time that the feeds should be switched to and away from the master control feed, to locally-broadcasted commercials.
An example of a cable company DTMF sequence code would communicate the following to the cable company's broadcast equipment:
SWITCH TO LOCAL NOW - SWITCH TO LOCAL NOW - PREPARE TO SWITCH BACK - PREPARE TO SWITCH BACK - SWITCH BACK TO NATIONAL NOW - SWITCH BACK TO NATIONAL NOW - "IF YOU HAVEN'T SWITCHED BACK TO NATIONAL NOW, DO SO IMMEDIATELY"
DTMF signaling in the cable industry went away because it was distracting to viewers, it was susceptible to interference when DTMF tones were sounded by characters in television shows (a character dialing a Touch-Tone telephone in a television show might convince the cable company computers to switch away from a "hot feed" to dead air), and the cost of human-imperceptible signaling technologies decreased. This article is about the novel Dead Air for other uses of the term see Dead air.
In-band signalling applies only to Channel Associated Signalling (CAS). See also Signalling (telecommunications Channel Associated Signaling (CAS also known as Per-Trunk Signaling (PTS is a form of digital communication signaling In Common Channel Signaling (CCS) separate channels are used for control and data, as opposed to the shared channel in CAS, so all control is out-of-band by definition. See also Signaling (telecommunications In telephony Common Channel Signaling (CCS or in the US Common Channel Interoffice Signaling (CCIS is the transmission
In computer programming, magic numbers are used for in-band signaling of file formats. In Computer programming, the term magic number has multiple meanings
When out-of-band communication is unavailable, one of two techniques may be used to preserve network transparency. Out-of-band is a technical term with different uses in Communications and Telecommunication. In Telecommunications transparency can refer to The property of an entity that allows another entity to pass thorough it without altering either of the
- Encapsulation: The bundling of the control data in the packet's header and then removing the header (and/or footer) of the packet at the far end, restoring the data to be the same as the original. In Information technology, a packet is a formatted unit of Data carried by a Packet mode Computer network. In Information technology, header refers to supplemental Data placed at the beginning of a block of data being stored or transmitted
- Bit Stuffing: The insertion of noninformation or escape characters to modify, synchronize and justify the data so it never looks like signaling information (and remove the stuffed bits and escape codes at the far end, restoring the data to be the same as the original). In Data transmission and Telecommunication, bit stuffing (also known—uncommonly—as positive justification) is the insertion of noninformation bits In Computing and Telecommunication, an escape character is a single character which in a sequence of characters signifies that what is to follow takes an alternative
See also
External links
- InBandSignal from the Portland Pattern Repository
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic