Custom Calling Features

Custom Calling Features. Also known as custom local area signaling services (CLASS), these are a suite of enhanced telephone services offered by local exchange carriers beyond standard plain old telephone service (POTS). They provide subscribers with greater control over incoming calls, offering functionalities like selective call blocking and distinctive ringing patterns. The development and deployment of these features were closely tied to the modernization of the public switched telephone network (PSTN) and the advent of Signaling System No. 7 (SS7). Their adoption marked a significant shift in user interaction with the telephone network, preceding the more advanced capabilities of Voice over IP (VoIP) systems.

Definition and Overview

These services are defined as value-added functionalities provided by a telephone company operating within the North American Numbering Plan or other national networks. They operate on the subscriber's local loop and are typically managed through a combination of network-based intelligence and customer premises equipment. The overarching goal is to enhance the basic telephony experience by filtering, identifying, or managing calls based on predefined subscriber preferences. Regulatory bodies like the Federal Communications Commission (FCC) have historically governed the provisioning and tariffs associated with these services, distinguishing them from the core regulated offerings of AT&T and the Bell System before its breakup.

Common Features

A standard portfolio includes several widely recognized capabilities. Caller ID displays the originating number, and sometimes a name from a CNAM database, on a compatible device before the call is answered. Call waiting emits an audible tone to indicate an incoming call while the line is in use, allowing the subscriber to toggle between conversations. Three-way calling enables a conference between the subscriber and two other parties. Distinctive ring assigns unique ringing patterns to calls from specific pre-programmed numbers. Call forwarding allows all calls to be redirected to another designated number, while selective call rejection automatically blocks calls from up to a specific quantity of unwanted numbers. Other features include call return (to redial the last incoming number), repeat dialing, and anonymous call rejection, which blocks calls from parties who have blocked their caller ID information.

Implementation and Technology

The implementation of these features relies heavily on the capabilities of the central office switch, such as those manufactured by Nortel Networks, Lucent Technologies, or Ericsson. The transition from electromechanical switches to digital switching systems like the 5ESS Switch or DMS-100 was a prerequisite for their widespread rollout. The intelligent network functionality is enabled by Signaling System No. 7 (SS7), a protocol suite that separates call control signaling from the voice path, allowing for rapid querying of databases and feature activation. Subscriber interaction is often managed through a vertical service code, such as dialing *69 for call return. The features are provisioned on a per-line basis and are stored in network databases like the Service Control Point (SCP), interacting with the Service Switching Point (SSP) at the switch.

Historical Development

The conceptual origins lie in early Bell Labs research into network intelligence. Widespread deployment began in the late 1980s and accelerated throughout the 1990s, driven by the digitalization of the network following the Modification of Final Judgment that broke up the Bell System. Regional Bell Operating Companies (RBOCs) like BellSouth, Ameritech, and U S West competed by marketing these features aggressively. The development of the CLASS industry standard ensured interoperability between equipment from different manufacturers, such as Siemens and Alcatel-Lucent. This period also saw legal and regulatory debates, including rulings by the Supreme Court of the United States regarding the privacy implications of caller ID services.

Business and Residential Use

In residential markets, these features became a significant source of incremental revenue for carriers like Verizon and CenturyLink, often bundled into packages. They fundamentally changed social and communication etiquette, as documented by researchers at institutions like the Massachusetts Institute of Technology Media Lab. For businesses, especially small offices, features like call forwarding and distinctive ring provided rudimentary call center functionality without private branch exchange (PBX) investment. The advent of competitive local exchange carriers (CLECs) and later Voice over IP providers like Vonage and Skype incorporated and expanded upon these concepts, offering them as software-based features. Today, while still available on traditional POTS lines, their core functionalities are seamlessly integrated into the service offerings of modern mobile network operators and cloud communications platforms such as RingCentral and Microsoft Teams. Category:Telecommunications services Category:Telephone exchange equipment