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SDH PrincipleSDH PrincipleV1.1V1.1

2

ContentsContents

SDH Overview

Frame Structure

Overhead

3

SDH OverviewSDH OverviewLimitation of PDH

Advantages of SDH over PDH

4

Limitations of PDH Limitations of PDH 1. Interface

Electrical interfaces

There are only regional standards, instead of universal standards

Optical interfaces

No unified standards for optical line equipments, manufacturers develop equipment according to their own standards.

5

European Series

565Mb/s565Mb/s

139Mb/s139Mb/s

34Mb/s34Mb/s

8Mb/s8Mb/s

2Mb/s2Mb/s

×4

×4

×4

×4

Japanese Series North American Series

1.6Gb/s1.6Gb/s

400Mb/s400Mb/s

100Mb/s100Mb/s

32Mb/s32Mb/s

6.3Mb/s6.3Mb/s

1.5Mb/s1.5Mb/s

274Mb/s274Mb/s

45Mb/s45Mb/s

6.3Mb/s6.3Mb/s

×4×4

×4

×4

×6

×7

×3

×5

64Kb/s64Kb/s

×24 ×30

×3

×3

Limitations of PDH Limitations of PDH

6

Limitations of PDH Limitations of PDH 2. Multiplexing Method

Asynchronous Multiplexing

Code rate justification is required for matching and accepting clock difference.

The locations of the low-rate signals in high-rate signals are not regular nor fixed.

7

Limitations of PDH Limitations of PDH

140/34 Mb/s 34/140Mb/s

34/8 Mb/s 8/34 Mb/s

8/2 Mb/s 2/8 Mb/s

2 Mb/s

Optical/Electrical Electrical/Optical

multiplexingdemultipexing

Adding and Dropping in PDH

8

Limitations of PDH Limitations of PDH 3. Operation and Maintenance

PDH signal frame structure has very few overhead bytes for Operation, Administration, and Maintenance (OAM).

4. Network Management Interface

No universal network management interface for PDH network.

9

Advantages of SDH over PDHAdvantages of SDH over PDHDefinition of SDH (Synchronous Digital Hierarchy):

SDH defines the frame structure, multiplexing method, transmission rate, and interface code pattern

10

Advantages of SDH over PDHAdvantages of SDH over PDH1. Interface

Electrical interfaces

SDH provides a set of standard rate levels----STM-N.

(N= 4n =1, 4, 16, 64……).

The basic signal transmission structure level is STM-1, at a rate of 155Mb/s.

Optical interfaces

Optical interfaces adopt universal standards. Line coding of SDH signals involves scrambling, instead of inserting redundancy codes.

11

Advantages of SDH over PDHAdvantages of SDH over PDH2. Multiplexing Method

low-rate SDH signals → high-rate SDHSignals via byte interleaved multiplexing method

PDH signals → SDHSynchronous multiplexing method and flexible mapping structure

12

Advantages of SDH over PDHAdvantages of SDH over PDH3. Operation and Maintenance

Abundant overhead bits are used for OAM.

Unnecessary to add redundancy bits to monitor line performance during line coding.

4. CompatibilitySDH network and the existing PDH network can work together.

SDH network can accommodate the signals of other hierarchies such as ATM, FDDI, and Ethernet.

13

ContentsContents

SDH Overview

Frame Structure

Overhead

14

SDH Frame StructureSDH Frame Structure

Byte-oriented block structure

Frame transmission rate: 125µs (8000 frames/sec)

9×270×N Bytes

1

345

9

SOH

STM-N Payload(including POH)

Transmission Direction

9×N 261×N270×N

SOH

AU PTR

15

SDH Frame StructureSDH Frame StructurePayload – area for services transmission in STM-N

2M, 34M, and 140M signals are packed and carried in the payload of STM-N frame over SDH network. If STM-N frame is a truck, the payload area is the carriage of the truck.

Path Overhead (POH) – after packing low rate signals, POH is added to monitor the transmission of every packet. This process is like attaching a label on the packet.

16

SDH Frame StructureSDH Frame StructureSection Overhead (SOH) – monitors the whole STM-N frame, i.e. monitor performance of all packages in the carriage of the truck.

Regenerator Section Overhead (RSOH) – monitors the whole STM-N frame.

Multiplex Section Overhead (MSOH) – monitors each STM-1 of the STM-N frame.

RSOH, MSOH, and POH compose the integrated monitoring system of SDH.

17

SDH Frame StructureSDH Frame StructureAU Pointer (AU-PTR) – used for alignment of lower rate signals in the payload of STM-N frame to accurately locate the payload.

AU-PTR is added in transmitting end, when the signal is packed into the payload of STM-N frame. The process could be to setting a coordinate value to identify where the package is in the carriage.

At receiving end, the low rate signal is dropped from STM-N frame according to the AU-PTR value. The process could compare to getting the package from the carriage according to above coordinate value.

Since packages are byte interleaved, the entire payload could be dropped once the first package is identified through alignment.

18

SDH Frame StructureSDH Frame StructureWhen the rate of the signal to multiplex is lower, for low-speed signals like 2M & 34M, 2-level pointer alignment is necessary.

First of all, packing the low rate signals, like 2M or 34M into apacket;

Secondly, aligning the signal in the packet by TU Pointer (TU-PTR);

Thirdly, multiplexing the above lower rate packet into another higher rate packet by AU-PTR.

19

SDH Frame StructureSDH Frame Structure

2-level pointer alignment

AU-PTR

TU-PTR

2M

34MAU-PTR

TU-PTR

2M

34M

20

Synchronous Multiplexing StructureSynchronous Multiplexing StructureMultiplexing structure

Low order SDH frame → high order SDH frame: 4 in 1 byte interleavePDH → STM-N: synchronous multiplexing and flexible mapping

140M → STM-N34M → STM-N2M → STM-N

ITU-T G.709 defines a complete set of multiplexing structures, in which multiplexing of PDH signal into STM-N frame is not unique and every country or area adopts one particular structure.

21

ITU-T G.709 Multiplexing StructureITU-T G.709 Multiplexing Structure

Virtual Container

STM-N140Mb/s

45 Mb/s34 Mb/s6.3Mb/s

2Mb/s

1.5Mb/s

x3

x7

x7

x1x3

C-11

C-12

C-2

C-3

C-4

VC-11

VC-2

VC-3

VC-3

VC-4

TU-11

TU-12

TU-2

TU-3

TUG-2

TUG-3

AUG

AU-3

AU-4

VC-12

x3

x4

x1

Container

Tributary Unit

Administrative Unit

Tributary Unit Group

Administrative Unit Group

Synchronous Transmission Module

Alignment

Multiplexing

Mapping

xN

22

Multiplexing Structure in ChinaMultiplexing Structure in China

Mapping

Alignment

Multiplexing

STM-N AUG AU-4 VC-4

TU-3 VC-3 C-3

C-4

TUG-2 TU-12 VC-12 C-12

TUG-3

xN

139264 kb/s

34268 kb/s44736 kb/s

2048 kb/s

x3

x7

x3

23

Multiplexing of 140M into STM-1Multiplexing of 140M into STM-1

C-4: Container-4 is the standard information structure for 140M signal, implementing rate adjustment.

VC-4: Virtual container-4 is the standard information structure corresponding to C-4, monitoring the real-time performance of the carried 140M signal.

1

140MRate adjustment/ packing C-4

1 2609

125 µs

Add POH for monitoring/ packing VC-4

POH

1 1

9

125 µs1 261

Next page

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Multiplexing of 140M into STM-1Multiplexing of 140M into STM-1

AU-4: Administrative Unit 4, the information structure corresponding to VC-4.

Multiplexing process: 140M → VC-4 → AU-4 → STM-1

Consequently, only one 140M signal can be multiplexed into STM-1

Pointer alignment

1 270

AU PTR AU-41 9

10 270

Add SOH

RSOH

MSOHPayload

AU PTR

1

9

1 270×N1

9

STM-N

125 µs 125 µs

25

Multiplexing of 34M into STM-1Multiplexing of 34M into STM-1

C-3: Container 3 is the standard information structure for 34M signal, implementing rate adjustment.

VC-3: Virtual Container-3 is the standard information structure corresponding to C-3, monitoring the real-time performance of the carried 34M signal.

1 1

34M C-3

1 849

125 µs

Add POH for monitoring/packing VC-3

POH

9

125 µs1 85

Next page

Rate adjustment/ packing

26

Multiplexing of 34M into STM-1Multiplexing of 34M into STM-1

TU-3: Tributary Unit-3, the standard information structure corresponding to VC-3, implementing the first level pointer.

TUG-3: Tributary Unit Group-3, the standard information structure corresponding to TU-3.

Multiplexing process: 34M → VC-3 → TU-3 → TUG-3, 3×TUG-3 → VC-4 →STM-1

Consequently, three 34M signals can be multiplexed into one STM-1.

First level pointer alignment

1 8686

Fill in gapTU-3

1H1H2H3

1

9

H1H2H3

R

TUG-3 Byte interleave

1

9 9

11 261

×3

POH

R R VC-4

27

Multiplexing of 2M into STM-1Multiplexing of 2M into STM-1

C-12: Container-12 is the standard information structure for 2M signal, implementing rate adjustment. Four basic frames compose a multi-frame.VC-12: Virtual Container-12 is the standard information structure corresponding to C-12, monitoring the real-time performance of the carried 2M signal.TU-12: Tributary Unit-12, the standard information structure corresponding to VC-12, implementing the first level pointer.

2M

125 µsBasic frame POH

速率适配

1 4

C-12

1

9

Add POH for monitoring

First level pointer alignment

VC-12 TU-12

1 1 441 1

9 9

Next Page

Rate adjustment

28

Multiplexing of 2M into STM-1Multiplexing of 2M into STM-1

TUG-2: Tributary Unit Group-2. TUG-3: Tributary Unit Group-3.

Multiplexing process:

2M → C-12 → VC-12 → TU-12; 3×TU12→ TUG-2; 7×TUG-2 → TUG-3; 3×TUG-3 → VC-4 → STM-1.

Consequently, 63( = 3x7x3) 2M signals can be multiplexed into STM-1. The multiplexing structure of 2M is 3-7-3 structure.

1 12

TUG-2

1

9

R R TUG-3

1 86

Byte interleave

Byte interleave

x 7x 3 x 3

Byte interleave

29

Mapping and Multiplexing ProcedureMapping and Multiplexing Procedure

STM-N

x Nx N x 1C-12C-12VC-12VC-12VC-4 TUG-2AUG-4 AU-4 TU-12TU-12 2Mb/s2Mb/s

Rate adjustment

LPOH

TU-PTR

AU-PTR

x３Multiplexing

x7 Multiplexing

HPOHxN Multiplexing

TUG-3

x３Multiplexing

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ContentsContents

SDH Overview

Frame Structure

Overhead

31

OverheadOverheadOverhead implements the monitoring functions to ensure proper transport of the payload.

Section Overhead- includes RSOH & MSOH

Path Overhead- includes HPOH & LPOH

32

Section OverheadSection OverheadTransmission direction

A1 A1 A1 A2 A2 A2 J0B1 E1 F1D1 D2 D3

Administrative Unit Pointer (AU PTR)

B2 B2 B2 K1 K2D4 D5 D6D7 D8 D9D10 D11 D12S1 M1 E2

RSOH

MSOH

9 columns

9 rows

Reserved for national use Media dependent bytes

33

A1, A2 BytesA1, A2 BytesFraming Alignment Bytes: A1, A2

To identify the initial location of a frame

A1=F6 H, A2=28 H

OOF is reported

OOF lasts 3 m seconds

LOF is reported

A1, A2 cannot be detected for five consecutive frames;

34

J0 ByteJ0 ByteRegenerator Section Trace Byte: J0

As the identification of regenerator section access point, it ensures that a section receiver can verify its continued connection to the intended transmitter.

It is used to identify individual STM-1 inside a multiplexed STM-N. STM-16 has sixteen J0 bytes for every STM-1 in it.

35

F1 ByteF1 ByteUser Channel Byte: F1

Provides a 64 kb/s data/voice channel for special maintenance purposes.

36

D1-D12 BytesD1-D12 BytesData Communication Channel (DCC) Bytes: D1-D12

DCC is the channel for transmission of OAM information among NEs and NMS.

192kp/s (3 x 64 = 192) channel is defined using bytes D1, D2, and D3 as a Regenerator Section DCC.

576kp/s (9 x 64 = 576) channel is defined using bytes D4 to D12 as Multiplex Section DCC.

37

E1, E2 BytesE1, E2 BytesOrderwire Bytes: E1, E2

E1 and E2 are used to provide 64 kb/s channels for voice communication.

E1 is accessed at regenerators as well as at all multiplex points

E2 is accessed only at Multiplexers

38

B1 ByteB1 ByteBit Interleaved Parity (BIP-8) Byte: B1

B1 is for regenerator section error monitoring.BIP-8 is computed over all bits of the regenerator section of STM-N frame. BIP-8 Principle:

B1 is computed in unit of 8 bits.Monitoring partition: bit column.Even parity is generated by setting the BIP-8 bits so that there is an even number of 1s in each partition of the signal.

39

B1 ByteB1 ByteB1 Byte Principle

At transmitting side, the BIP-8 is computed over all bits of the STM-N regenerator before scrambling, and the result is placed in byte B1 of the preceding frame.

At receiving end, the BIP-8 is computed over all bits of the regenerator after de-scrambling. This result is then Exclusive OR with the B1 byte result received in later frame.

If the value of Exclusive OR operation is zero, there is no bit block error. But if the result is not zero then there may be errors in transmission.

A1 00110011 A2 11001100 A3 10101010 A4 00001111

B 01011010

BIP-8For example

BIP-8 is computed over a frame of signal composed of 4 bytes.

40

B1 ByteB1 ByteAt transmitting end A, BIP-8 is computed over all bits of the first frame, and result is placed in byte B1 of the second frame. At receiving end B, the BIP-8 is computed over all bits of the first frame, and then exclusive OR with the B1 byte of the second frame. The number of 1s of exclusive OR operation indicate transmission errors.

1stframe

A B

1st frame1st frame

Transmitting end

2ndframeNth

frame

Nth frame

2ndframe2nd

frame

Receiving end

41

B2 BytesB2 BytesBit Interleaved Parity Nx24 (BIP-Nx24) Byte: B2

B2 is for multiplex section error monitoring.

The BIP-N x 24 is computed over all bits of the STM-N frame except for the first three rows of SOH.

BIP-N x 24 Principle:

B2 is computed in unit of N x 24. Monitoring block: bit column.Even parity is generated by setting the BIP-N x 24 bits so that there is an even number of 1s in each block of the signal.

42

B2 BytesB2 BytesB2 Byte Principle

At transmitting end, the BIP-Nx24 is computed over all bits of the STM-N frame except for the first three rows of SOH, and the result is placed in 3 bytes B2 of the preceding frame before scrambling.

At receiving end, the BIP- Nx24 is computed over all bits of the frame except for the first three rows of SOH, and then Exclusive OR with the B2 bytes of the later arrived frame.

If the value of Exclusive OR operation is zero, there is no bit block error. Any mismatch in result indicates transmission errors.

For example

BIP-N×24 is computed over a frame of signal composed of 9 bytes.

11001100 11001100 11001100

01011101 01011101 01011101

11110000 11110000 11110000BIP24

01100001 01100001 01100001

43

M1 ByteM1 ByteMultiplex Section Remote Error Indication (MS-REI) Byte: M1

A return information from receiving end detecting MS-BBE to transmitting end.

Convey the count of interleaved bit blocks that have been detected in error by BIP-24 in receiving end.

The transmitting end will report a corresponding performance event, MS-REI.

44

K1, K2 BytesK1, K2 BytesAutomatic Protection Switching (APS) Bytes: K1 & K2

Last three bits of K2 byte indicates alarm type;111 indicates MS-AIS alarm (Multiplex Section Alarm Indication Signal) at receiving end.

110 stands for MS-RDI alarm (Multiplex Section Remote Defect Indication) at transmitting end.

45

S1 ByteS1 ByteSynchronization Status Message Byte: S1 (b5-b8)

S1 is used to implement clock source protection and switching function.

The value corresponding to b5-b8 indicates the quality of synchronization. The smaller values indicates better quality of the clock sources.

46

Section OverheadSection OverheadByte interleaving of Section Overhead

When STM-1 frames are multiplexed into STM-N, the byte interleave multiplexing way of AU Pointer and Payload is different from Section Overhead. In former case, all bytes are interleaved. For the later, only the first STM-1 frame’s section overhead is reserved, while remaining STM-1 frame’s Section Overheads are omitted except few bytes like A1, A2, B2.

47

Path OverheadPath OverheadClassification

High Order Path Overhead (HPOH)

Low Order Path Overhead (LPOH)

48

HPOHHPOH

Path trace byte J1B3C2G1F2H4F3K3N1

VC4

1

1

261

9

Path BIP-8 byte

Signal label byte

Path status byte

Path user channels byte

Position indicator byte

Network operator byte

(b1~b4) APS channel byte

Path user channels byte

49

J1 ByteJ1 BytePath Trace Byte: J1

The first byte of VC4

Pointed by AU-PTR

Required to be matched at transmitting and receiving ends

50

B3 ByteB3 BytePath BIP-8 Code: B3

Implements higher order VC’s error monitoring Monitoring principle: BIP-8 even parity The value of B3 byte needs to be compared at both transmitting and receiving ends. Any inconsistency between two results means transmission errors in VC-4.

51

C2 ByteC2 ByteSignal Label Byte: C2

Indicates the composition and type of multiplexing structureExamples:00H means unused02H means multiplexing structure is 3xTUG-3Indicate the information about payload typeRequired match at both ends

52

G1 ByteG1 Byte

Path Status Byte: G1Indicating high order VC transmission status

Return message from receiving end to transmitting endHP-REI: Higher Order Path Remote Error indication (sum of receiving error block of VC4)

HP-RDI: High Order Path Remote Defect Indication

53

H4 ByteH4 Byte

Multi-frame Indicator Byte: H4Indicate the multi-frame types and location of the payload.

For 2M PDH to SDH multiplexing structure, H4 indicates the current frame is which frame of the multi-frame, allowing Rx to find TU-PTR and drop 2M signals.

H4 value: 00H-03H

54

Low Order Path OverheadLow Order Path Overhead

V5: Path status, Path BIP-2, and Signal Label Byte

J2: Low order path trace byte

N2: byte for network operator usage

K4: APS byte for low order path

11

9

500µs VC12 Multi-frame

V5 J2 N2

VC12 VC12VC12

4K4

VC12

55

V5 ByteV5 BytePath Status, Path BIP-2, & Signal Label Byte: V5

The first byte of VC-12 multi-frame

Pointed by TU-PTR

Monitor error block, signal label, path statusError block monitoring: b1-b2

Return path status message: b3, b8

Signal label: b5-b7

Similar to B3, C2, and G1

56

SDH Frame StructureSDH Frame StructureUnderstanding SOH and POH?

Both SOH and POH are bytes for Operation, Administration, and Maintenance (OAM), which ensure reliable and flexible transmission.

SOH and POH monitor and administrate transmission at different layers (or levels). RSOH and MSOH are for regenerator section and multiplex section respectively. Whereas, HPOH and LPOH are for VC-4 / VC-3 and VC-12 respectively.

57

SDH Frame StructureSDH Frame StructureComparison

LPOH – to monitor small package (VC-12)

HPOH – to monitor large package (VC-3/VC-4)

MSOH – to monitor the carriage of the truck (STM-1)

RSOH – to monitor the motorcade which consists of trucks (STM-4 / STM-16 / STM-64)

58

Hierachy of common alarmsHierachy of common alarms

R-LOS R-LOF

MS-EXC MS-AIS

AU-LOP AU-AIS HP-UNEQ HP-TIM HP-SLM

TU-AIS

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