Overview of international standards for transmission impairments affecting digital telecommunications networks

In moving into an era based on the integration of digital transmission and switching facilities, it is necessary to identify those impairments that can arise in a digital network and to establish appropriate performance objectives.

Within the International Telecommunications Union (ITU), one of the International Telegraph and Telephone Consultative Committees (CCITT) has been working in this field. Study Group XVIII has, over the last four year study period, been developing CCITT Recommendations and establishing performance objectives for some of the more significant impairments that can affect transmission through digital networks.

The study period ended in October 1984 when the CCITT Plenary Assembly approved the new and revised Recommendations prepared by SGXVIII. The work is far from complete and new study questions have been prepared for consideration during the next study period.

The aim of the paper is to increase the general awareness of the reader to the existence, scope and importance of these emerging international standards.

More specifically, the paper outlines the range of impairments that can arise in digital networks, namely errors, slips, jitter, wander, delay, short breaks and non-availability. Regarding the status of international standardisation, the CCITT current position is reviewed and, where appropriate, some of the overall performance objectives are included in the paper.