Travelling wave (TW) based protection functions, which process the time of arrival of TWs, require high sampling rates in the range of hundreds of kilohertz to several megahertz. In digital substations merging units (MU) publish the sampled values of current and voltage signals on process-level networks. However, publishing these highly sampled signals for TW-based protection functions limits severely the number of MUs in a process-level network due to the significant increase of communication load. To circumvent this problem, distributed signal processing units (DSPU) extract directly the necessary signal features and publish these at a lower publishing rate in order to decrease the communication load. This paper provides an mathematical analysis on the scalable integration of DSPUs in deterministic process-level networks based on the High-availability Seamless Redundancy (HSR) protocol, time-aware network nodes and traffic scheduling. It is shown that the distributed signal processing architecture provides a scalable integration of high sampling rate measurements for TW-based protection functions. Lastly the analytical model has been validated through a discrete-event simulation.