The Service Evaluation System (SES) was an

operations support system Operations support systems (OSS), operational support systems in British usage, or Operation System (OpS) in Nippon Telegraph and Telephone, NTT are computer systems used by telecommunications service providers to manage their networks (e.g., tele ...

developed by

Bell Laboratories Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, the company operates several lab ...

and used by telephone companies beginning in the late 1960s. Many local, long distance, and operator circuit-switching systems provided special dedicated circuits to the SES to monitor the quality of customer connections during the call setup process. Calls were selected at random by switching systems and one-way voice connections were established to the SES monitoring center. During this era, most voice connections used analog trunk circuits that were designed to conform with the Via Net Loss plan established by Bell Laboratories. The purpose of the VNL plan and five-level long distance switching hierarchy was to minimize the number of trunk circuits in a call and maximize the voice quality of the connections. Excessive loss in a voice connection meant that subscribers may have difficulty hearing each other. This was particularly important in the 1960s when dial up data connections were developed with the use of analog modems. The SES evaluated

multi-frequency In telephony, multi-frequency signaling (MF) is a type of signaling that was introduced by the Bell System after World War II. It uses a combination of audible tones for address ( telephone number) transport and supervision signaling on trunk ...

outpulsing signaling as well as voice impairments including sound amplitude, noise, echo, and a variety of other parameters. Deployment of common-channel signaling systems such as Common Channel Interoffice Signaling and later Signaling System #7 obviated the need to monitor

signaling as it became obsolete. The Service Evaluation System was described in Notes on the Network published by

AT&T AT&T Inc., an abbreviation for its predecessor's former name, the American Telephone and Telegraph Company, is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the w ...

in 1970, 1975, 1980 and later versions published by Bell Communications Research (now Telcordia Technologies) in 1983, 1986, 1990, 1994, and 2000.

References

{{Reflist Telecommunications standards Telecommunications systems