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Telecommunication Systems Spring 2010

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Synchronous Digital Hierarchy (SDH) is an international standard for transmitting digital information over optical networks. It multiplexes multiple low-rate signals into higher transmission rates, with each signal having a defined frame structure. The STM-1 (155.52 Mbps) serves as the base signal, with higher levels being integer multiples of this rate. SDH ensures that data signals are synchronized through a central clock, while supporting both synchronous and plesiochronous networks. This system plays a crucial role in modern telecommunication infrastructures.

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Telecommunication Systems Spring 2010

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  1. Telecommunication Systems Spring 2010

  2. ynchronous igital ierarchy S D H

  3. SDH What is it ?? Synchronous Digital Hierarchy is the international standard for transmitting digital information over optical networks

  4. SDH • The Concept ! • Signals with a higher transmission rate are obtained by multiplexing several low rate signal • Every signal in the hierarchy levels has a specific frame structure • All multiplex levels are positive integer multiples of the base signal

  5. SDH • Synchronous Signals !! • Data signals which have same nominal transmission rates, but come from different sources, controlled by a central clock frequency are clock aligned to each other

  6. SDH • Plesiochronous Signals !! • Data signals which have same nominal transmission rates, but come from different sources, have slightly higher or lower value than the nominal bit rate • There is a small amount of variation between them, such signals are almost synchronous to each other and therefore termed as Plesiochronous

  7. SDH • Plesiochronous Network • The individual link sections are not synchronous to each other • Synchronous Network • In synchronous network, the link sections are synchronous to each other

  8. SDH • PDH multiplex hierarchies !

  9. SDH • PDH multiplex hierarchies !

  10. STM-N Nx155.52Mbps STM-16 2.05 Gbps STM-4 622.08 Mbps SDH • What is STM-1?? • ITU-T defined the STM-1 (Synchronous transport module -1), 155.52 Mbps as base signal for SDH • All multiplex levels are positive integer multiples of this base signal (STM-1)

  11. SDH • Structure of an STM-1 frame !! • The two dimensional representation of an STM-1 frame includes 9 rows with 270 bytes each • The sequence of transmission is top left to bottom right

  12. SDH • Structure of an STM-1 frame !!

  13. SDH • Transmission rate of STM-1 ??

  14. SDH • Structure of an STM-1 frame !! • STM-1 frame has three types of blocks • Section Overhead • PTR (pointer) • Payload

  15. SDH • Multiplexing technique ! • Byte Interleaving (byte-by-byte multiplexing)

  16. SDH • Structure of an STM-1 frame !! • Every STM frame is transmitted 8000 times per second • Every byte in an STM-1 frame has a transmission capacity of 64 kbps

  17. SDH • Multiplexing technique !

  18. SDH • Mapping of ATM cells ! • Prior to their transmission, ATM cells are interleaved into the container C-4 (Mapping)

  19. SDH • Mapping of ATM cells ! • A C-4 is provided every 125 micro seconds • An ATM cell can be transmitted via two C-4

  20. SDH • Mapping of ATM cells ! • In order to transmit container C-4 in the STM-1, container specific supplementing is necessary • The C-4 receives a path over head with a size of 9 bytes

  21. SDH • Mapping of ATM cells ! • The block resulting from C-4 and POH is called virtual container VC-4

  22. SDH • MAPPING OF ATM CELLS ! • THERE IS A FLOATING EMBEDDING OF VC-4 INTO THE STM-1 FRAME PAYLOAD • PART OF THE VC-4 MAY BE TRANSMITTED IN ONE STM FRAME AND ANOTHER PART IN THE NEXT STM FRAME

  23. SDH • Mapping of ATM cells ! • The pointer indicates start of the Virtual container 4 in the payload

  24. SDH • Mapping of ATM cells ! • Component of the STM-1, inside which a VC-4 is able to float and which consists of the block PTR and payload is known as Administrative unit 4 (AU-4)

  25. SDH • Mapping of ATM cells ! • In the AU-4, pointer is abbreviated AU-4 PTR

  26. SDH • Mapping of ATM cells ! • To complete the STM-1 frame section overhead is added to AU-4

  27. SDH • Mapping of ATM cells ! • Individual steps of creating an STM-1

  28. SDH • Mapping of ATM cells ! • In SDH, containers with a fixed capacity are provided every 125 micro second • Incorporation of ATM cells into STM

  29. SDH • SDH Products !!

  30. Thank You

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