Informational signaling informs the originator, or calling party, as to the status of a dialed call and also rings the called party to advise of a call presence. Informational signaling is often referred to as call-progress signaling and includes the following five types of signaling conditions.
• Dial tone— Certain predefined frequency pairs are used to convey informational signaling. A dial tone results from the generation of a continuous 350 and 440 Hz frequency pair by the telephone company switch or local PBX.
• Ringing signal— When a call is routed to its intended destination, the service switch or PBX sends a 20 Hz 86-VAC (volts alternating current) ringing signal that cycles for 2 seconds on and 4 seconds off.
• Ringback signal— When a call is in a ringing state, the ringback tone informs the caller as such. The ringback tone consists of a 400 and 48 Hz frequency pair. Like the ringing signal, it cycles on for 2 seconds and off for 4 seconds.
• Busy signal— When a call cannot be completed because the intended, or called, destination line is in use, the local PBX or switch generates a busy signal back to the calling party. The busy signal cycles between the frequency pair of 480 and 620 Hz for 1/2 second (0.5) on followed by a 1/2 second off.
• Fast busy signal— When a call cannot be completed because of trunks between switches being busy, a fast busy signal is sent. The fast busy signal consists of the same frequency pair as a regular busy, 480 and 620 Hz, but is cycled on for 0.2 seconds and off for 0.3 seconds. The local telephone company switch or corporate PBX generates the fast busy signal upon indications that it cannot find a trunk to carry the call beyond the local switch/PBX.
ANI, or automatic number identification, is a service that provides the telephone number of an incoming call. ANI is used for a variety of functions. By receiving the incoming telephone number, telephone companies can direct a call to the proper long-distance carriers equipment, help identify the callers address for 911 calls, and route 800 number calls to the nearest vendor. Call centers can also use ANI to identify the calling party to better service a customer.
ANI numbers, sometimes referred to as ANIs, are constructed per the NANP.
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