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.
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.
More bang for Bruck ; An X-ray machine developed in Goa prods change in Siemens AG's global approach to the low and middle market.
Oct 02, 2011; You know what a submarine is?" asks Armin Bruck. The Managing Director of Siemens in India is not referring to the literal...
IBM ThinkPad Developed in Boca Raton, Fla., Will Go Along for Indy 500 Ride. (Originated from The News, Boca Raton, Fla.)
May 30, 1994; May 29--When Indy 500 race car driver Emerson Fittipaldi hits top speeds at today's race he will have a little help from a gadget...