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Understanding Synchronous Digital Hierarchy (SDH) in Advanced Communications

This lecture, presented by Matthew Luckie from the University of Waikato, explores the principles of Synchronous Digital Hierarchy (SDH), the dominant standard for digital telecommunications networks. It covers key concepts such as self-healing rings, operations and maintenance (OAM), and fault location. The structure and functioning of STM-1 frames, including frame rates, overheads, and multiplexing methods are discussed. Students will also learn about the role of add-drop multiplexers and digital cross-connects, crucial for managing network traffic and ensuring system resilience.

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Understanding Synchronous Digital Hierarchy (SDH) in Advanced Communications

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Presentation Transcript

  1. COMP514 – Advanced Communications Lecture 2: SDH Matthew Luckie mluckie@cs.waikato.ac.nz

  2. Lecture Outline • SDH : Synchronous digital hierarchy • Self-healing rings • OAM • Fault location

  3. Synchronous Digital Hierarchy (SDH) • Dominant standard for digital telecommunications networks

  4. STM-1 • STM-1 frame rate 8000/second • 125 microseconds • STM-1 frame 270 columns by 9 rows • 2430 bytes / 19440 bits • 19440 * 8000 = 155.52 Mbps

  5. STM-1 Frame Regenerator Section Overhead (RSOH) PathOverhead AU Pointer 9 Rows Multiplexer Section Overhead (MSOH) InformationPayload Section Overhead (9 bytes) Payload (261 bytes)

  6. STM-1 / STM-n • STM-1 frames begin with A1/A2 frame alignment bytes. • Receiver can watch for this sequence every 125us to gain synchronisation • STM-n is formed by byte-multiplexing STM-1 frames. • STM-4 frame begins withA1 A1 A1 A1 A2 A2 A2 A2

  7. DXC DXC DXC DXC DXC DXC DXC DXC DXC ADM ADM ADM ADM ADM ADM ADM ADM ADM ADM ADM ADM SDH Networks Backbone RegionalNetworks ADM ADM ADM Local Metro Networks Customers C C C C

  8. SDH Multiplexers • Add-drop multiplexers allow individual streams to be added or removed from the STM-1 STM-n STM-n ADM

  9. SDH Multiplexers • Digital Cross Connects (DXC) demux the entire stream and switch channels to other SDH circuits • Core equipment will break down to STM-n rate • Edge equipment will break down entire stream DXC STM-n STM-n STM-n

  10. SDH Repeater • A repeater regenerates the optical signal

  11. Self Healing Rings Bidirectional links between nodes

  12. Self Healing Rings Bidirectional links between nodes

  13. Self Healing Rings Bidirectional links between nodes

  14. Operations and Maintenance (OAM) • Goals of OAM are • Performance monitoring • Fault detection • Fault notification • System protection • Point-of-fault identification

  15. OAM • Hierarchical structure • F1: Repeater section • F2: Digital section • F3: Transmission path • F4: Virtual Path (VP) • F5: Virtual Channel (VC)

  16. OAM for ATM 8 7 6 5 4 3 2 1 • If the first twobits of payloadtype field are1 and 0 • OAM cell • 100 : segment • 101 : end-to-end Virtual Path Identifier (VPI) Virtual Channel Identifier (VCI) Payload Type CLP CRC

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