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Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Each square carries a letter. To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares.
Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. You can also try the grid of 16 letters. Letters must be adjacent and longer words score better. See if you can get into the grid Hall of Fame !
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In telecommunications, in-band signaling is the sending of metadata and control information within the same band or channel used for voice (e.g. DTMF Tones) and can be heard by the callers, as opposed to out-of-band signals (e.g. SS7 control signals) which cannot be heard as they are on a different channel or band.
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 signaling 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 signaling 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.
As a method of in-band signaling, DTMF tones were also used by cable television broadcasters to indicate the start and stop times of local 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 signaling applies only to Channel Associated Signaling (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, an example of in-band signaling are magic numbers, used for signaling of file formats.
||This article needs additional citations for verification. (January 2008)|