In-band signaling


In-band signaling

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.

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. The tones "control" the telephone system by instructing the telephone company's equipment where to route the call to. These control tones are sent over the same channel and in the same band (300Hz to 3.4kHz) 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. Examples of this kind of in-band signalling system are SS5 and R2.

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. 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.

In-band signaling is insecure because it exposes control signals, protocols and management systems to the user(s), which may result in falsing. In the case of the blue boxes that were popular in the 1960s and 1970s, such falsing was deliberate. 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.

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. 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.

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. 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.

In-band signalling applies only to Channel Associated Signalling (CAS). 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.

In computer programming, magic numbers are used for in-band signaling of file formats.

When out-of-band communication is unavailable, one of two techniques may be used to preserve network transparency.
* 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.
* 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).

See also

*Out-of-band signaling
*Line signaling

External links

* from the Portland Pattern Repository


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Out-Of-Band Signaling —   [engl.], Außenbandübertragung …   Universal-Lexikon

  • out-of-band signaling —    Use of narrowband filters to place the voice signal on a carrier channel below 3,400 cps, reserving the 3400 3700 cps band for supervisory signals …   IT glossary of terms, acronyms and abbreviations

  • out-of-band signaling —    The transmission of control information on frequencies outside the bandwidth available for a voice or data transfer. The separation is usually accomplished by means of a filter …   Dictionary of networking

  • Signaling System 7 — Signaling System #7 (SS7) is a set of telephony signaling protocols which are used to set up most of the world s public switched telephone network telephone calls. The main purpose is to set up and tear down telephone calls. Other uses include… …   Wikipedia

  • Signaling (telecommunications) — In telecommunication, signaling (signalling in British spelling) has the following meanings: the use of signals for controlling communications the information exchange concerning the establishment and control of a telecommunication circuit and… …   Wikipedia

  • Signaling System 7 — Signaling System #7 (SS7) ou système de signalisation #7 est un ensemble de protocoles de signalisation téléphonique qui sont utilisés dans la grande majorité des réseaux téléphoniques mondiaux. Sa principale application est l établissement et la …   Wikipédia en Français

  • signaling, in-band —    A type of signaling using an AC signal (usually 2600 Hz) within the normal voice band. This signal can be transmitted from end to end of a long voice circuit without an intermediate signaling equipment. Since the signaling is audible, the… …   IT glossary of terms, acronyms and abbreviations

  • Signaling (Wirtschaftswissenschaft) — Grundidee der Prinzipal Agent Theorie (P: Prinzipal, A: Agent) Die Prinzipal Agent Theorie (auch Agenturtheorie) ist innerhalb der ein Teilgebiet der . Sie bietet ein Modell, um das Handeln von Menschen in einer zu erklären, aber trifft auch… …   Deutsch Wikipedia

  • Signaling System 7 — Signalisierung Unter Signalisierung versteht man in der Telekommunikation die Übertragung von Steuerinformationen. Einfache Signalisierungsinformation sind zum Beispiel klingeln oder Teilnehmer besetzt. Weiter gibt es Signalisierungsinformationen …   Deutsch Wikipedia

  • Out-of-band — The term out of band has different uses in communications and telecommunication. In case of out of band control signaling, signaling bits are sent in special order in a dedicated signaling frame. D channel in ISDN is an example of out of band and …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.