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Synchronous Digital Hierarchy

Synchronous Digital Hierarchy. Eleventh Meeting. History of Multiplexing. Synchronous digital hierarchy (SDH) is a world-wide standard for digital communication network. Two other systems were before it: the plesiochronous digital hierarchy (PDH) and frequency division multiplexing (FDM).

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Synchronous Digital Hierarchy

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  1. Synchronous Digital Hierarchy Eleventh Meeting

  2. History of Multiplexing • Synchronous digital hierarchy (SDH) is a world-wide standard for digital communication network. • Two other systems were before it: • the plesiochronous digital hierarchy (PDH) and • frequency division multiplexing (FDM). • Frequency division multiplexing (FDM): • a number of signals share a medium that has a much larger bandwidth. • Support of many stages

  3. Time Division Multiplexing (two ways)

  4. Plesiochronous Digital Hierarchy • Basic data transfer rate is 2048 Kbps • It is broken in • 30 x 64Kbps • 2 x 64Kbps (synchronization and signaling) • The exact are of the 2Mpbs is controlled by a clock with some percentage +/- %0.005 • What is Justification or Stuffing • Extra bits that are need to reconstruct correctly

  5. Synchronous Transport Module (STM) • STM-1 Frame • STM-1 frame is designed this way because • transport the full range of PDH bit-rates • provide sufficient flexibility to transport future services based

  6. Building transport (interleaving) • The transmission of digital signals over optical fibre allows for transmission rates far in excess of the 155.52 Mbit/s defined as the aggregate rate for STM-1. • STM- 4 622.080 Mbit/s • STM-16 2488.32 Mbit/s • STM-64 9953.28 Mbit/s

  7. SDH Multiplexing Structure

  8. STM1 Frame • Equals to 9 × 270 byte block. • AU-4 = payload area (9 × 261) • The pointer address is located in row four of the overhead • The location of the start of the VC-4 • The floating nature of the virtual containers and the pointer is one of the key features of SDH. • The VC-4 occupies the whole payload area of the AU-4.

  9. VC-4 holds Lower-order virtual containers, Tributary unit (TU) pointers Indicate the start position of lower-order VCs. The AU-4 pointer marks the location of the beginning of VC-4 TU pointers Have a fixed position within the VC-4. Mark the start of lower-order VCs. AU-4 Pointer

  10. Simple Transmission System • Two connected multiplexers on an optical link • Containing three regenerators. • SDH signals is sent to a distant location, • Logical signal is converted to a physical signal. • Carried out by the STM-n multiplexer. • Signals are attenuated and distorted • The regenerator detects the incoming optical signal and ‘regenerates’ a perfectly formed signal with the same information content. • The distant STM-1 multiplexer receives the optical signal and reconverts it into a logical signal for processing. Generators

  11. Overhead • Overhead functionality two types. • operation and maintenance of the SDH signal itself • Provides framing, identification and alarm indication. • error performance indication and data communications channels, • Provide error performance monitoring and an embedded management communication channel.

  12. regenerator section overhead(RSOH) multiplex section overhead (MSOH). A1 and A2 bytes together contain a frame alignment word. The frame alignment word is repeated with each frame to maintain alignment and re-alignement. When STM-1 signals are multiplexed into an STM-4, then the C1 byteallows each STM-1 to be uniquely identified. The B2 bytes provide an error monitoring capability (D1 to D12) is to provide an embedded data communications link Section overhead

  13. Y Z X C1 A1 A1 A1 C1 A1 A1 A1 C1 A1 A1 A1 Alignment Example Expected: A1 Read: A1 Source: Z

  14. Y Z X C1 A1 A1 A1 C1 A1 A1 A1 C1 A1 A1 A1 Alignment Example Expected: A1 Read: A1 Source: X

  15. Y Z X C1 A1 A1 A1 C1 A1 A1 A1 C1 A1 A1 A1 Alignment Example Expected: A1 Read: A1 Source: Y

  16. Y Z X C1 A1 A1 A1 C1 A1 A1 A1 C1 A1 A1 A1 Alignment Example No reading because of attenuation

  17. Y Z X C1 A1 A1 A1 C1 A1 A1 A1 C1 A1 A1 A1 Alignment Example Expected: C1 Read: C1 Source: X

  18. Y Z X C1 A1 A1 A1 C1 A1 A1 A1 C1 A1 A1 A1 Alignment Example Expected: C1 Read: C1 Source: Y

  19. Y Z X C1 A1 A1 A1 C1 A1 A1 A1 C1 A1 A1 A1 Alignment Example Require Alignment Expected: C1 Read: A1 Source: Z

  20. Path Overhead • 9 bytes, arranged in one column, dedicated to management and supervision of that path.

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