Editing In-band signaling (section)

==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 (communications)|channel]], the copper wire, and in the frequency range (300&nbsp;Hz to 3.4&nbsp;kHz) as the audio of the telephone call. In-band signaling is also used on older telephone carrier systems to provide [[Interexchange carrier|inter-exchange]] information for routing calls. Examples of this kind of in-band signaling system are the [[Signaling System No. 5]] (SS5) and its predecessors, and [[R2 signalling]].<ref>{{Cite book |url=https://books.google.com/books?id=YH_LBQAAQBAJ&q=signaling%2520system%2520ss4&pg=PA844 |title=The Telecommunications Illustrated Dictionary, Second Edition |last=Petersen |first=J. K. |date=2002-05-29 |publisher=CRC Press |isbn=9781420040678 |pages=844 |language=en}}</ref><ref>{{Cite book |url=https://books.google.com/books?id=VfPST6NEggEC&q=ccitt%2520ss1&pg=SA4-PA8 |title=Telecommunication Switching Systems and Networks |last=V.S.Bagad |date=2009 |publisher=Technical Publications |isbn=9788184315905 |pages=388 |language=en }}{{Dead link|date=September 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{Cite web |url=https://www.cisco.com/c/en/us/support/docs/voice/digital-cas/5717-e1-r2-sig.html |title=E1 R2 Signaling Theory |website=Cisco |language=en |access-date=2018-01-05}}</ref>

Separating the control signals, also referred to as the control plane, from the data, if a [[Transparency (telecommunication)|bit-transparent]] connection is desired, is usually done by [[Escape sequence|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 [[end user]]s, which may result in [[falsing]].  In the 1960s and 1970s, so-called ''[[phone phreaks]]'' used [[blue box]]es for deliberate falsing, in which the appropriate tones for routing were intentionally generated, enabling the caller to abuse functions intended for testing and administrative use and to make free long-distance calls.

Modems may also interfere with in-band signaling, in which case a [[guard tone]] may be employed to prevent this.