EGEC4120 - Telecommunication Networks Chapter 8

EGEC4120 - Telecommunication Networks and Switching - Chapter 8: PDH/SDH/SONET

• E-book Reference: Introduction to Telecommunications, Network Engineering (second Edition) by Tarmo Anttalainen. Available at https://ebookcentral.proquest.com/lib/uomp/reader.action?docID=227647

• Course Authors: Analene Montesines Nagayo and Mohamed Yusuf Hasan

• Outcome Coverage (OC 3): Design and manage a Digital Transport network such as SDH/SONET.

• PDH (Plesiochronous Digital Hierarchy): An early digital hierarchy for transmission, standardized by ITU-T and CCITT. The higher-order multiplexers in PDH operate according to their own independent clock frequencies.

• SDH (Synchronous Digital Hierarchy): A synchronous digital hierarchy; unlike PDH, SDH is used with digital multiplexers in exchanges, combining different hierarchies with varied bit rates.

• SONET (Synchronous Optical Network): A synchronous optical network that utilizes light-emitting diodes (LEDs) or lasers for optical fiber communication. Removing synchronization problems and restoring plesiochronous digital hierarchy (PDH) systems, it was developed for bulk telephone and data exchange. It is designed for high-bit-rate optical transport, carrying all PDH types in one universal structure.

• SONET Limitations: PDH systems were standardized decades ago. The need for access to tributary rates requires a step-by-step de-multiplexing process. Optical interfaces lack standardization but are vendor-specific. Network management, features, and specific interfaces from different vendors often aren't compatible. High data rates (above certain numbers) aren't standardized, copper interfaces are defined, and overhead percentage increases with rate.

• SONET Layers:

  • Path Layer: Responsible for signal movement from source to destination. STS Multiplexer/Demultiplexer components provide this layer's functions.
  • Line Layer: Manages signal movement across a physical line. STS Multiplexer/Demultiplexer and Add/Drop Multiplexer provide the functionalities for this layer.
  • Section Layer: Manages signal movement across a physical section. Each network device is responsible for functionalities at the section layer.
  • Photonic Layer: Corresponds to the physical layer of the OSI model, including physical specs for the optical fiber channel.

• SONET Components:

  • STS Multiplexer: Multiplexes signals from various electrical sources to create optical signals.
  • STS Demultiplexer: Demultiplexes optical signals into corresponding electrical signals.
  • Regenerator: A repeater that regenerates and strengthens optical signals.
  • Add/Drop Multiplexer: Allows inserting and removing signals from a given path.

• SONET Network Topology:

  • Unidirectional Path-Switched Ring (UPSR): Traffic flows in one direction around a ring. If a link fails, traffic re-routes in the opposite direction.
  • Bidirectional Line-Switched Ring (BLSR): Traffic flows in both directions. When a failure occurs, traffic re-routes to a protective path on the opposite side of the ring.

• SONET vs SDH:

  • They are high-speed optical communication networks.
  • SONET uses a 9x90 grid (9 rows, 90 columns) frame structure, while SDH uses a 9x270 grid.
  • SONET uses STS (Synchronous Transport Signal) and VT (Virtual Tributary) while SDH uses STM (Synchronous Transport Module) and VC (Virtual Container).
  • SONET has a fixed payload rate of 51.84 Mbps, while SDH has multiple variable payload rates, including 155.52 Mbps, 622.08 Mbps, and 2.5 Gbps.

• SONET STS-1 Frame:

  • 90 columns x 9 rows = 810 bytes
  • 8000 frames per second

• STM-1 Frame Structure has 270 columns.

• SONET Advantages: Reduced network complexity, flexible topologies, high data rates, and efficient bandwidth management.

• Drill Problems:

  • Problem 1: Calculate the data rate and DS1 channels in a SONET STS-3 frame.
  • Problem 2: Calculate the ATM cell transmission rate in an OC-12 connection. (Provides relevant example calculations.)