Twenty-Five Years of Applications of the Modified Allan Variance in Telecommunications

Abstract

The Modified Allan Variance (MAVAR) was originally defined in 1981 for measuring frequency stability in precision oscillators. Due to its outstanding accuracy in discriminating power-law noise, it attracted significant interest among telecommunications engineers since the early 1990s, when it was approved as a standard measure in international standards, redressed as Time Variance (TVAR), for specifying the time stability of network synchronization signals and of equipment clocks. A dozen years later, the usage of MAVAR was also introduced for Internet traffic analysis to estimate self-similarity and long-range dependence. Further, in this field, it demonstrated superior accuracy and sensitivity, better than most popular tools already in use. This paper surveys the last 25 years of progress in extending the field of application of the MAVAR in telecommunications. First, the rationale and principles of the MAVAR are briefly summarized. Its adaptation as TVAR for specification of timing stability is presented. The usage of MAVAR/TVAR in telecommunications standards is reviewed. Examples of measurements on real telecommunications equipment clocks are presented, providing an overview on their actual performance in terms of MAVAR. Moreover, applications of MAVAR to network traffic analysis are surveyed. The superior accuracy of MAVAR in estimating long-range dependence is emphasized by highlighting some remarkable practical examples of real network traffic analysis.

The Companion of Enrico’s Chart for Phase Noise and Two-Sample Variances

“…The ITU-T Recommendation G.8260 [32] compares ADEV, MDEV, and TDEV from the standpoint of telecommunications. MDEV seems the favorite tool in telecommunications [97] and enables the direct calculation of TDEV using (41). However, MDEV takes 50% longer acquisition time T .…”

The Enrico's Chart for Phase Noise and Two-Sample Variances

“…The ITU-T Recommendation G.8260 [70] compares ADEV, MDEV and TDEV from the standpoint of telecommunications. MDEV seems the favorite tool in telecommunications [17], and gives TDEV using (39). However, MDEV takes 50% longer measurement time T .…”