A scalable architecture for integrated SDH/SONET framers is presented. It exploits the fact that not only those framer functions that are obviously suited for parallel processing but all SDH/SONET overhead processing and most of the payload processing functions can be implemented as distributed algorithms. Thereby an M/spl times/STM-N framer also handles STM-M/spl times/N and STM-(M/spl times/N)c frames. These distributed algorithms cover frame scrambling, overhead byte processing, ATM and PPP payload handling, and interface implementations. A series of modular building blocks for this architecture and first complete framers is now available.

In the field of communications, an ever-increasing number of system functions is realized in digital form. In this context, the problem of economical analog/digital conversion becomes an important issue. The cost of analog/digital conversion, however, is often dominated by the associated filters required for the prevention of foldover distortion. For this reason, an approach characterized by analog filtering (with relaxed requirements) before A/D conversion, and additional, digital, time-shared filtering after A/D conversion, becomes an attractive solution. In this paper, the signal-to-noise ratio of such a system is analyzed. The analysis includes quantization noise and overload distortion from the analog/digital conversion process, additional noise due to codec imperfections and round-off noise from the digital filters and interpolators. A design example, that was also implemented in hardware, demonstrates that the specifications of the CCITT can be easily met.

The paper treats linear and nonlinear methods that refine the delta modulation process. These methods improve the quality of the decoded signal at a given transmission rate. Two linear processes are analyzed. The first one matches the source signal to the coder for minimum weighted noise in the decoded signal. The second one influences the signal which is fed to the comparator; it shapes the spectrum of the quantization noise desirably. Two nonlinear methods used in the delta modulation process are discussed. The first achieves a best possible prediction of the future signal from past binary decisions and thus a reduction of the error signal. The methods of the second type make the coder adaptive to variations in the power level of the source signal. This results in a large dynamic range of the coding system. A comparison of the various methods is made and a coding system for speech signals, based on a suitable combination of these methods, is described.