scope:

SCOPE AND PURPOSE

Standardization of electrical interfaces for the digital hierarchy, at rates ranging from DS1 through STS3 and above, has been determined a necessary function to assure interoperability of both equipment and networks.

Information in the digital hierarchy is transported via cable pairs or coax links by either of two means:

By signals represented by the presence or absence of pulses occurring within specific time slots or,

By signals consisting of continuous pulses encoded to represent binary ones and zeros.

Pulse mask and eye pattern templates have been established by ANSI and ITU-T (CCITT) to provide information on the signals allowable at interface points. In conjunction with other specifications such as signal power, bit rate, and line code, these pulse masks and eye patterns, are used to ensure compatible operation of equal-level DS-n and STS-n signals at interface points provided by the DSX-n and STSX-n Cross Connects. In principle, however, none of the existing waveform specifications - isolated pulse templates for DS1 thru STS1 or eye patterns for STS1¹, STS3, and above - provide a direct measure of transmission performance at the system level.

This technical report provides an introduction to the basis for the use of pulses masks and eye patterns to determine signal characteristics at specific electrical interface points in the digital network. Included are definitions and discussions of desired signal parameters, a review of various measurement techniques used to verify that the desired parameters are met, and an interpretation of the observed results when measurements are performed using first a non-inductive resistive load and then when the signals are terminated by their normal (reactive) sink.

¹ STS1 is described by both pulse mask and eye pattern specifications.