PDH: Advantages and Disadvantages of Plesiochronous Digital Hierarchy

This page explores the advantages and disadvantages of Plesiochronous Digital Hierarchy (PDH), outlining its benefits, drawbacks, and fundamental principles.

What is PDH?

Introduction:

• PDH stands for Plesiochronous Digital Hierarchy.
• It’s a technology associated with digital exchanges.
• PDH combines different hierarchies of digital signals, each having different data rates. Tributaries can contain 24 or 30 channels, or multiples thereof.
• PDH combines inputs that have the same data rates but originate from different clock sources.
• Europe uses 30 channels, while North America uses 24 channels. Japan utilizes different PDH levels.
• Bit interleaving is employed to combine these signals.

PDH level hierarchy in North America

Benefits or Advantages of PDH

Here are the benefits and advantages of PDH:

• It was designed to support the transportation of large amounts of data over digital equipment using various transmission mediums, such as microwave radio or fiber optic systems.
• Network management is significantly enhanced.
• PDH functions independently and effectively in North America, Europe, and Japan according to their respective standard specifications.

Drawbacks or Disadvantages of PDH

Here are the disadvantages of PDH:

• PDH uses different frames for transmission and in the data layer, leading to complex multiplexing and de-multiplexing processes.
• Accessing a lower tributary requires de-multiplexing the entire system.
• The maximum capacity for PDH is 566 Mbps, which can be a bandwidth limitation in modern applications.
• Tolerance is allowed in bit rates.
• PDH only supports point-to-point configurations.
• PDH doesn’t support a hub architecture.
• Different manufacturers have their own standards, and PDH has varying multiplexing hierarchies, which can make integrating interconnecting networks difficult.