plesiochronous digital hierarchy

Plesiochronous Digital Hierarchy (PDH) is a system used in telecommunications to transmit multiple data streams simultaneously over long distances. "Plesiochronous" means "nearly synchronized," indicating that the different data channels run at almost the same speed but may have slight timing differences. PDH allows efficient multiplexing — combining several smaller data signals into a larger one — enabling communication networks to handle increasing data traffic. Although it has been mostly replaced by newer technologies, PDH was a fundamental method for managing voice and data transmissions in the past, providing a scalable way to transmit multiple data channels over fiber or cable networks.