What is SS7?

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  • Written By: Malcolm Tatum
  • Edited By: Bronwyn Harris
  • Last Modified Date: 06 October 2019
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While the term SS7 is commonly used in the United States, it is not an accepted acronym around the world. Here are some facts about the nature, function, and applications of SS7 technology around the world, including the other names for the system.

With a proper name of Signaling System #7, SS7 technology is a set of signaling protocols developed specifically for telephone communication protocols. Originally developed by AT&T in 1975, these protocols today provide the underpinning for public switched telephone networks around the world. The name used to identify the protocols varied from place to place. For instance, SS7 technology is known simply as C7 in the United Kingdom, CCSS7 in other parts of North America, and more recently as ITU-T in other parts of the world.


SS7 was originally designed to replace earlier signaling technology that was beginning to experience more failures as the demand for voice communications continued to increase around the world. With the earlier versions of signaling protocols, the basis was an in-band signaling process, where the set up process for initiating calls was activated by the playing of special tones into the lines. Referred to as bearer channels, this earlier technology became problematic as touch-tone technology led to persons discovering they could bypass the special keys used by operators to initiate these protocols. Devices that could emit a series of tones and thus hit on a working combination were beginning to cause quite a bit of confusion and in some cases would overload an already busy communications grid.

SS7 technology solved both problems at once. By moving into signaling protocols that were protected and out of band, it was not possible to emulate the tones any longer to trigger telephony activity. This effectively eliminated the hijacking of the phone channels and freed up the communications grid to process legitimate requests for voice communications. The expansion into out of band tones also made the expansion of phone networks in a number of countries possible, since new channels could be added as needed.

SS7 also made a whole range of new services available to telephone subscribers. For example, many of us have grown accustomed to using star (*) commands in order to redial a last number, check dial tone or access a voice mailbox. The creation of SS7 also led to a number of support services that clients of various audio conference call bureaus can enjoy, such as the ability to dial out to a participant, signal for operator assistance, initiate a recording, and a roster of other options that help control the conference.

With the marriage of voice communications and the Internet, SS7 has proven to be perfectly compatible with online phone service options, allowing for what is referred to as switch to dedicated service with no problem. In other words, someone who uses an Internet phone service is still able to call someone who uses traditional landline services, with no degradation in sound clarity. This is possible due to SS7 protocols, as is the growing use of Voice over Internet Protocol (VoIP) to process international telephone calls.


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Post 1

What is SS7?

(A) A signaling standard used in message switched digital networks

(B) A switching standard used in digital networks

(C) A switching standard used in analog networks

(D) A signaling standard used in packet switched digital networks

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