SDH and Fiber Optics Study Notes

INTRODUCTION TO THE SYNCHRONOUS DIGITAL HIERARCHY (SDH)

CHAPTER 1 - ABSTRACT/BACKGROUND

  • Overview of SDH:

    • SDH (Synchronous Digital Hierarchy) represents an international standard aimed at high-speed telecommunication over optical and electrical networks.

    • Capable of transporting digital signals with variable capacities.

    • Characterized as a synchronous system, facilitating a flexible yet simplified network infrastructure.

    • Origins trace back to standard bodies around 1990, leading to significant advancements in optical fiber communication networks regarding performance and cost.

  • History of Digital Transmission:

    • 1970s: Introduction of PCM (Pulse Code Modulation) into telecom networks, enabling multiplexing of 32 PCM streams to achieve a rate of 2.048 Mbit/s (E1).

    • PDH (Plesiochronous Digital Hierarchy) was used for higher multiplexing rates.

    • 1985: Bellcore proposed SONET (Synchronous Optical Networking).

    • 1988: Introduction of the SDH standard designed to unify transmission rates into a mapping hierarchy.

CHAPTER 2 - PDH

  • Definition:

    • PDH stands for Plesiochronous Digital Hierarchy, which allows for the structured multiplexing of signals.

  • Multiplex Levels:

    • Common data rates include:

    • 2.048 Mbit/s

    • 8.448 Mbit/s

    • 34.368 Mbit/s

    • 139.264 Mbit/s

  • Error Definitions:

    • AIS: Alarm Indication Signal

    • LOS: Loss of Signal

    • LOF: Loss of Frame

  • Plesiochronous Multiplexing:

    • Refers to a system that is nearly synchronous but not perfectly so.

    • A typical setup multiplexes 2 Mbit/s service signals to 140 Mbit/s, requiring intermediate stages (8 Mbit/s and 34 Mbit/s multiplexers).

    • PDH necessitates more equipment for alarm management and performance oversight.

CHAPTER 3 - SDH

  • What is SDH?:

    • SDH employs synchronous multiplexing, allowing data from multiple sources to interleave bytes.

    • Channels are multiplexed in fixed positions associated with the framing byte.

    • Demultiplexing allows individual channels to be selectively dropped without affecting other streams.

  • Advantages of SDH over PDH:

    • Establishes a worldwide digital format standard.

    • Introduces optical interface standards, enhancing networking capabilities.

    • Flexible multiplexing structure, permitting efficient add-and-drop traffic handling.

    • Offers improved management capabilities, enabling back-and-forth compatibility between legacy PDH and future ISDN requirements.

  • When to Use SDH:

    • To enhance network capacity, flexibility, survivability, and reduce operational costs.

  • SDH Rates:

    • Based on multiples of 155.52 Mbit/s.

    • Basic unit: STM-1 equals 155.52 Mbit/s.

    • Higher units:

    • STM-4 = 622.08 Mbit/s

    • STM-16 = 2,588.32 Mbit/s

    • STM-64 = 9,953.28 Mbit/s

CHAPTER 4 - CONCLUSION

  • Advantages of SDH:

    • High transmission capacity, replacing most PDH systems.

    • Serves both legacy telephone networks and modern packet-switched broadband networks (ATM, IP).

    • Innovative features such as VCAT (Virtual Concatenation) and LCAS (Link Capacity Adjustment Scheme) enhance flexibility and capability.

CHAPTER 5 - SDH SYNCHRONIZATION - TIMING LOOP ISSUE

  • Timing Issue Overview:

    • Timing loops can lead to severe frequency errors within an SDH network due to internal clock tracking issues.

    • Often, timing loops occur without alarms to indicate their presence.

  • Modes:

    • Free-running Mode: Relies entirely on the internal clock of the Timing Clock and Control (TCC) card.

    • Holdover Mode: Activates when external timing references are lost, allowing the internal clock to provide continuity temporarily based on past data.

  • Synchronization Quality Requirements:

    • Compliance with ITU-T standards for network element clock performance and synchronization functions.

    • Limitations on the number of tandem network elements to prevent timing loops.

  • Prevention Measures for Timing Loops:

    • Implementing diverse technical solutions and verifying synchronization quality.

CHAPTER 6 - FIBER OPTICS VS COPPER CABLES

  • Definition:

    • Fiber optics utilize light to transmit information, offering advantages over traditional copper mediums in aspects of distance, bandwidth, and interference resistance.

  • How Fiber Works:

    • Based on total internal reflection, light pulses are transmitted through highly pure glass fibers.

  • Comparison Factors:

    • Bandwidth: Fiber optics have a capacity that far exceeds copper wire, significantly reducing signal loss over long distances.

    • Electromagnetic Interference (EMI): Optical fibers are immune to EMI, offering greater security and reliability.

    • Size and Weight: Fiber optics are smaller and lighter than copper cables, making them easier to install while allowing expansive deployments.

    • Electrical Safety: Fiber optic cables do not carry electrical currents, eliminating shock and fire hazards associated with copper wires.

CHAPTER 7 - HIGH-SPEED BROADBAND (HSBB) IN TM

  • Overview:

    • HSBB aims to enhance Malaysia's telecommunications capabilities, promising significantly faster broadband speeds.

    • Deployments will target urban areas and industrial zones to ensure broad access.

  • Goals:

    • Supports national economic growth and fosters competitive positioning within the region through enhanced broadband infrastructure, matching or exceeding international standards.

CHAPTER 8 - GLOSSARY

  • Key Terms:

    • MTIE: Maximum Time Interval Error

    • TDEV: Time Deviation

    • PDH: Plesiochronous Digital Hierarchy

    • SDH: Synchronous Digital Hierarchy

    • SSMB: Synchronization Status Message Byte

    • SETS: Synchronous Equipment Timing Source

    • SSU: Synchronization Supply Unit

DOCUMENT REVIEW HISTORY

  • Chain of Edits:

    • Document revised on 15-Dec-2008, with major content contributions by various experts.