This 3 sentence document summary provides an overview of the key information from the source document: This document discusses design considerations for the time base unit of Italy's first digital switching system deployed in the national telecom network (Gruppi Speciali) in 1971. The switching system was developed by CSELT and first installed in Mestre, Venice in 1972. The time base unit was a critical component that provided timing signals for the digital switching system.

1. PIERO BELFORTE March 1971
DESIGN CONSIDERATIONS FOR THE TIME BASE
UNIT OF THE FIRST DIGITAL SWITCHING
SYSTEM DEPLOYED IN THE ITALIAN TELECOM
NETWORK (GRUPPI SPECIALI).
THIS SWITCHING SYSTEM WAS DEVELOPED BY CSELT in
1971 and INSTALLED IN MESTRE (Venice) in 1972.