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SDH Principles

SDH Principles. Course Contents. Chapter 1 Emergence of SDH . ---- Synchronous Digital Hierarchy ---- It defines frame structure, multiplexing method, digital rates hierarchy and interface code pattern. What is SDH?. ---- Need for a system to process increasing amounts of information.

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SDH Principles

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  1. SDH Principles

  2. Course Contents

  3. Chapter 1 Emergence of SDH ---- Synchronous Digital Hierarchy ---- It defines frame structure, multiplexing method, digital rates hierarchy and interface code pattern. What isSDH? ---- Need for a system to process increasing amounts of information. ---- New standard that allows mixing equipment from different suppliers. Why did SDH emerge?

  4. Plesiochronous Digital Hierarchy • 1-1 Disadvantages of PDH • interfaces • Electrical interface :- Only regional standards. 3 PDH rate hierarchies for PDH: European (2.048 Mb/s), Japanese, North American (1.544 Mb/s). • Optical interfaces:-No standards for optical line equipment, manufacturers develop at their will • Multiplexing methods • Asynchronous Multiplexing :- The location of low-rate signals in high-rate signals is not regular nor predictable. • OAM function • Weak Operation. • Weak Administration. • Weak Maintenance function. • Capabilities to setup a TMN is limited. 140 Mb/s 140 Mb/s 34 Mb/s 34 Mb/s 8 Mb/s 8 Mb/s de-multiplexer multiplexer 2 Mb/s

  5. 1-1 Advantages of SDH synchronous Digital Hierarchy • interfaces • Electrical interfaces:-Can be connected to all existing PDH signals. • Optical interfaces:-Can be connected to multiple vendors’ optical transmission equipment. • Multiplexing methods • Basic rate is STM-1, other rates are multiples of the basic rate • Low level SDH to/from high level SDH PDH signal to/from SDH signal. STM-64 10 Gb/s De-multiplexing STM-16 2.5 Gb/s ×4 STM-4 622 Mb/s STM-1 155 Mb/s ×4 622 Mbit/s ×4 622 Mbit/s Multiplexing 10 Gb/s WDM 2 Mbit/s

  6. 1-1-2 Advantages of SDH • OAM function • Abundant overheads bytes for automation, network monitoring and maintenance • Compatibility • Working with all kinds of signals like PDH, SDH, ATM & FDDI PDH, SDH, ATM, FDDI Signals packing package package STM-N STM-N SDH network Processing receive transmit Processing • Disadvantages of SDH • Mechanism of pointer adjustment is complex. • Large-scale application of software makes SDH system capable to receive viruses unpacking PDH, SDH, ATM, FDDI Signals

  7. Course Contents

  8. 2- SDH Frame Structure • From ITU-T G.707: • STM-1 is the basic transmission format • One frame lasts for 125 microseconds (8000 frames/s • Rectangular block structure 9 rows and 270 columns • Each unit is one byte (8 bits) • Transmission mode: Byte by byte, row by row, from left to right, from top to bottom Frame = 125 us 1 2 3 4 5 6 7 8 9 9 rows • Three parts: • Information Payload • Section Overhead • Pointer 9 270 Columns 1 byte = One 64 Kbit/s channel STM-N = 9 X 270 X N (N = 4, 16, 64) STM-1 rate = 9 X 270 X 8 X 8000 =155 Mb/s

  9. Information Payload • Information Payload • Also known as Virtual Container level 4 (VC-4) • Used to transport low speed tributary signals • Contains low rate signals and Path Overhead (POH) • Location: rows #1 ~ #9, columns #10 ~ #270 POH package POH loading and aligning low rate signal 9 rows package POH Data package 9 1 270 Columns

  10. Section Overhead • Fulfills the section layer OAM functions 1 2 3 5 6 7 8 9 • Types of Section Overhead • Regenerator Section Overhead (RSOH), monitors the whole STM-N • Multiplex Section Overhead (MSOH), monitors STM-1 in STM-N • √ Location: • RSOH: rows #1 ~ #3, columns #1 ~ #9 • MSOH: rows #5 ~ #9, columns #1 ~ #9 9 rows 9 270 Columns

  11. Pointer • Indicates the first byte of the payload container • Pointers permit phase and frequency differences of the VCs • Location: • row #4, columns #1 ~ #9 4 9 rows 9 270 Columns • Two stage alignment operation: AU-PTR 2nd alignment TU-PTR 1st alignment 2 M 34 M

  12. SDH Multiplexing Structure • Mapping • A process used when tributaries are adapted into VCs by adding justification bits and POH information • Aligning • This process takes place when a pointer is included in a Tributary Unit (TU) or an Administrative Unit (AU), to allow the 1st byte of the VC to be located • Multiplexing • This process is used when multiple low-order path signals are adapted into a higher-order path signal, or when high-order path signals are adapted into a Multiplex Section • Stuffing • As the tributary signals are multiplexed and aligned, some spare capacity has been designed into the SDH frame to provide enough space for all various tributary rates. Therefore, at certain points in the multiplexing hierarchy, this space capacity is filled with “fixed stuffing” bits that carry no information, but are required to fill up the particular frame • SDH Multiplexing Structure Legend • TUG = Tributary Unit Group • AUG = Administrative Unit Group • STM = Synchronous Transfer Module

  13. SDH Multiplexing Structure ×1 Mapping AUG-64 STM-64 Aligning ×4 Multiplexing ×1 AUG-16 STM-16 Pointer processing ×4 ×1 AUG-4 STM-4 Add AU pointer ×4 Packing Add POH ×1 ×1 AU-4 VC-4 C-4 AUG-1 STM-1 139264 kbit/s Add SOH Filling Gabs ×3 Add AU pointer Add POH Multiplexing Packing TU-3 VC-3 C-3 ×1 TUG-3 34368 kbit/s Filling Gabs ×7 TUG-2 Add AU pointer Add POH Multiplexing Packing TU-12 VC-12 C-12 2048 kbit/s ×3 Multiplexing

  14. Course Contents

  15. Part 3 Section Overheads ∆ = Media dependent bytes

  16. A1 and A2 Bytes • Framing Bytes • Indicate the beginning of the STM-N frame • The A1, A2 bytes are unscrambled • A1 = f6H (11110110), A2 = 28H (00101000) • In STM-N: (3XN) A1 bytes, (3XN) A2 bytes Framing Find A1,A2 N OOF Y stream over 3ms LOF STM-N STM-N STM-N STM-N STM-N STM-N AIS Next process Finding frame head

  17. D1 ~ D12 Bytes • Data Communications Channels (DCC) Bytes • Message-based Channel for OAM between NEs and NMS • RS-DCC – D1 ~ D3 – 192 Kbit/s (3X64 Kbit/s) • MS-DCC – D4 ~ D12 – 576 Kbit/s (9X64kbit/s) NE NE NE NE – DCC channel TMN OAM Information: Control, Maintenance, Remote Provisioning, Monitoring (Alarm & Performance), Administration

  18. E1 and E2 Bytes • Orderwire Bytes • Provides one 64 Kbit/s each for voice communication • E1 –RS Order wire Byte – RSOH order wire message • E2 –MS Order wire Byte – MSOH order wire message NE NE NE NE E1 and E2 Digital telephone channel E1-RS, E2-MS

  19. B1 & B2 Bytes • B1:- Bit interleaved Parity Code (BIP-8) Byte • A parity code (even parity), used to check the transmission errors over the RS • B1 BBE is represented by RS-BBE • B2:- Bit interleaved Parity Code (MS BIP-24) Byte – • This bit interleave parity NX24 code is used to determine transmission errors occurred over the MS • B2 BBE is represented by MS-BBE STM-N Rx Tx Calculate B1, B2 2#STM-N 1#STM-N BIP-8 Verify B1 B2 2#STM-N 1#STM-N

  20. K1 and K2 Bytes • K1 & K2(b1 ~ b5) bytes • Transmitting APS signaling (Automatic Protection Switching ) • Implement equipment self-healing function • Used for network multiplex • protection switch function • K2 (b6 ~ b8) • Multiplex Section Remote Defect Indication (MS-RDI): K2 (b6-b8) • Rx detects K2 (b6-b8)="111" generate MS-AIS alarm after 5 consecutive frames • Rx detects K2 (b6-b8)="110" generate MS-RDI alarm Start Detect K2(b6-b8) 110 111 Generate MS-AIS Generate MS-RDI Return MS-RDI

  21. S1& M1 Bytes • S1 byte:- • Synchronization Status Message Byte (SSMB): S1 (b5~ b8) • Value indicates the sync. level • Used to implement the clock source protection function • M1 byte:- • Multiplex Section Remote Error Indication（MS-REI）Byte • A return message from Rx to TX ,when RX find MS-BBE • A count of the number of BIP-24xN (B2) errors • TX generate corresponding performance event MS-REI Traffic Rx Tx Return M1

  22. Path Overheads Higher Order Path Overhead

  23. Path Overheads Path trace byte: J1 • Path BIP-8 Byte: B3 • Path bit interleaved parity code byte (even parity code) • Used to detect transmission errors(Performance Monitoring) • Calculated over all bits of the previous VC before scrambling and placed in the B3 of the current frame Detect J1 Verify B3 Match N Y Next process correct N Y HP-TIM • The first byte of VC-4 • User-programmable • Required match HP-BBE Next process Insert AIS downward

  24. Path Overheads • Signal label byte: C2 • Specifies the mapping type in the VC-N • 00 H  Unequipped • 02 H  TUG structure • 13 H  ATM mapping • Requires matching Detect C2 Detect receiving VC4 00H N Y HP-UNEQ HP-TIM HP-SLM Match Y N N Y HP-UNEQ • Path Status Byte: G1 • Return performance message from Rx to TX • HP-REI  b1 ~ b4 • HP-RDI  b5 HP-BBE Return HP-RDI N Y HP-SLM Next process Next process Return HP-REI Insert AIS downward

  25. Path Overheads • Error checking, Signal Label and Path Status of VC-12 V5 • First byte of the multi frame • Indicated by TU-PTR • b1 ~ b2  Error Performance Monitoring (BIP-2) • b3  Return Error detected in VC-12 (LP-REI) • b4  Return Failure declared in VC-12 (LP-RFI) • b5 ~ b7  Signal Label for VC-12 • b8  Indicate Defect in VC-12 path (LP-RDI) Detect V5 Low Order Path Overhead Detect b5-b7 Verify b1 b2 000 N Y match N Y LP-UNEQ Match Y N LP-BBE LP-SLM Return LP-REI b3 Next process Next process Return LP-RDI b8

  26. Pointers • AU-Pointer • Payload pointers permit differences in phase and frequency of the VC-N • Indicates the offset between VC payload & STM-N frame by pointing to 1st byte in VC • Divide the VC-4 payload bytes into 3 *783 units each unit is given an address  0 ~ 782 • H1 & H2 Bytes  Pointer bytes: • VC pointer bytes specify the VC frame location • Used to align the VC and STM-1 SOHs in an STM-N • Perform frequency justification • H3 Byte  Pointer action byte • Depending on the pointer value, the bytes are used as buffers for positive or negative pointer justifications • If receiver side cannot interpret the PTR value, AU-LOP then AIS alarms are inserted downwards “Receiving H1H2H3H3H3 all 1s, insert AU-AIS downwards” 3 x AU-3 1 = All 1s Y = 1001ss11 (S bits unspecified) 1 x AU-4

  27. Pointers • TU-Pointer • TU payload PTR allows dynamic alignment of the L-O VC-12 within the Multi frame • Payload PTR value is located in bits 7~ 16 of V1 & V2 Bytes • VC-12 Multi frame is divided into 140 units, each unit is 1 Byte. Each Byte has an address, Range 0~ 139, Unit 1 (Add = 0) is located after V2 Byte in the Multi frame • Indication of Multi frame in H4 Byte • If receiver side cannot interpret the PTR value, TU-LOP then AIS alarms are inserted downwards ”Receiving V1, V2, V3, V4 all 1s, insert TU-AIS downwards” TU Pointer

  28. SDH Networking Application

  29. Course Contents

  30. Chapter 1 Common SDH Network Topologies

  31. 1-1 Chain Network • Features of chain network: • All the nodes are connected one after the other • Both ends open • Advantages of chain network: • Cheap to build • Easy to operate , administrate and maintain • Disadvantages of chain network: • Services are difficult to protect • Applications of chain network • Railway Lines • Power Supply Lines

  32. 1-2 Star Network • Features of star network • A special node connected directly with other nodes • No direct connections between other nodes • Advantages of star network: • Capable of managing bandwidth • Disadvantages of star network: • Potential bottle neck • Equipment failure at the hub node • Applications of star network: • Access Networks • Rural Telephone Networks

  33. 1-3Tree Network • Features of star network • Combination of chain network and star network • Advantages of star network: • Capable of managing bandwidth • Disadvantages of star network: • Potential bottle neck • Equipment failure at the hub node • Applications of star network: • Broadcast Services

  34. 1-4 Ring Network • Features of star network • All nodes are connected together • Connect the two end nodes of a chain network to form a ring network • Advantages of star network: • Highly-reliable • Highly-survivable • Disadvantages of star network: • Complicated • Applications of star network: • The most common network- • -of modern SDH system

  35. 1-5 Mesh Network • Features of star network • Many nodes are interconnected together via direct routes • Advantages of star network: • No bottle neck • Very reliable • Disadvantages of star network: • Expensive • Complicated • Difficult to manage • Applications of star network: • Regions with large traffic • High hierarchy communication networks

  36. Course Contents

  37. Chapter 2 Common Network Elements

  38. 2-1 TM • Functions and Features: • PDH low rate signals <->STM-N • SDH signals<->STM-N • Electrical signals<-> Optical signals • Applications: • Point-to-point Network • Chain Network • Ring-chain Combination

  39. 2-2 ADM • Functions and Features: • PDH low rate signals <->STM-N • SDH signals<->STM-N • Electrical signals<-> Optical signals • Cross connections: • Tributary unit<->Eastward Line unit; • Tributary unit<-> Westward Line unit; • Eastward Line unit<->Westward Line unit • Applications: • Hub Network • Chain Network • Ring Network

  40. 2-3 REG • Functions and Features: • Signal regeneration • Amplification • Relaying • Applications: • Long-distance Transmission

  41. Course Contents

  42. Chapter 3 Introduction to SDH Network Protection

  43. 3- 1 Types of Survivable Network • Survivable Network • A network that is capable of restoring traffic in the event of a failure. • Automatically restore services • Within very short time (50ms) • Without manual intervention • Types of Survivable Network • Linear Multiplex Section Protection: • 1+1 Linear MS Protection • 1:N Linear MS Protection • Protection Rings • 2-fiber Unidirectional Path Protection Ring • 2-fiber Bidirectional Path Protection Ring • 2-fiber Bidirectional Multiplex Section Shared Protection Ring • 2-fiber Unidirectional Multiplex Section Dedicated Protection Ring • 4-fiber Bidirectional Multiplex Section Shared Protection Ring

  44. 3-1 Types of Survivable Network • Unidirectional Traffic • Traffic flow direction along the ring • Clockwise and counter-clockwise • Bidirectional Traffic • Traffic flow direction along the ring • Clockwise or counter-clockwise

  45. 3-2 Linear MS Protection • Switching modes of 1+1 linear MS protection system: • Unidirectional switching or Bidirectional switching • Revertive mode or Non-revertive mode • As a result: • Unidirectional switching in revertive mode • Unidirectional switching in non-revertive mode • Bidirectional switching in revertive mode • Bidirectional switching in non-revertive mode • APS protocol necessity • Unidirectional switching in non-revertive mode unnecessary • Other modes necessary

  46. 3-2-1 1+1 Linear MS Protection • Structure of 1+1 Linear MS Protection System • Protection mechanism of 1+1linear MS protection system: • Concurrent sending is permanent bridging • Selective receiving is switching

  47. 3-2-2 1:1 Linear MS Protection • Structure of 1:1 Linear MS Protection System • Protection mechanism of 1+1linear MS protection system: • Normal traffic flow

  48. 3-2-3 Linear MS Protection criteria • Linear MS protection is based on the MS (STM-1 within STM-N) • Protection switching criteria are SF and SD • SF (Signal Fail) includes RLOS, RLOF, MS-AIS, etc. • SD (Signal Degrade) includes B2-EXC, B2-SD • Those requiring the APS protocol • 1:N linear MS protection • uni- or bi-directional 1+1 linear MS protection in revertive modes • bidirectional 1+1 linear MS protection in non-revertive mode • This not requiring the APS protocol • unidirectional 1+1 linear MS protection

  49. 3- 3 Types of ring protection • Classifications of Protection Rings • Protected Traffic • Path protection ring • Multiplex section protection ring • Traffic Direction • Unidirectional protection ring • Bidirectional protection ring • Number of Optical Fibers • Two-fiber protection ring • Four-fiber protection ring

  50. 3- 3-1 Two-fiber bidirectional path protection ring • network is normal: • Protection switching mechanism:

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