(18) SDH Basic Concepts

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prohibited.

1

SDH Principle

ZTE University

Transmission Course Team


prohibited.

14

SDH Frame Structure

Byte-oriented block structure

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

Transmission Direction

1

3

4

5

9

SOH

STM-N Payload

(including POH)

9×N 261×N

270×N

SOH

AU PTR

9 x 270 x N Bytes


prohibited.

15

SDH Frame Structure

Payload – used to store service information in the frame

structure

2M, 34M, and 140M signals are packed and carried in the

payload of STM-N frame over SDH network. If STM-N

frame is the 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.


prohibited.

16

SDH Frame Structure

Section Overhead (SOH) – monitors the whole STM-N

frame, i.e. monitor the 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 comprise the integrated monitoring

system of SDH.


prohibited.

17

SDH Frame Structure

AU Pointer (AU-PTR) - aligns lower rate signals in the payload of

the STM-N frame so that it can be accurately located in the frame

AU-PTR is added in transmitting end, when the signal is packed into

the payload of STM-N frame. The process could be compared 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 be compared to

getting the package from the carriage according to a coordinate value.

Since packages are placed through byte interleaving, all of the payload

could be dropped once the first package is identified through alignment.


prohibited.

18

SDH Frame Structure

For low rate signals like 2M and 34M, 2-level pointer alignmentis necessary.

First, packing the low rate signal, like 2M or 34M into a packet;

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

Thirdly, multiplexing the above lower rate packet into another higher

rate packet, and aligning by AU Pointer (AU-PTR).


prohibited.

19

SDH Frame Structure

2-Level Pointer Alignment

AU PTR

TU PTR

2M

34M


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20

Synchronous Multiplexing Structure

Multiplexing Structure

Low order SDH frame → high order SDH frame: 4 in 1 byteinterleave

PDH → STM-N: synchronous multiplexing and flexiblemapping

ITU G.709 defines a complete set of multiplexing structures,in which multiplexing of PDH signal into an STM-N frame isnot unique and every country or area can adopt a particularstructure.


prohibited.

31

Overhead

Overhead implements the monitoring functions to

ensure proper transmission of the payload.

Section Overhead- includes RSOH & MSOH

Path Overhead- includes HPOH & LPOH


prohibited.

32

Section Overhead

Transmission

directionA1 A1 A1 A2 A2 A2 J0

B1 E1 F1

D1 D2 D3

Administrative Unit Pointer (AU PTR)

B2 B2 B2 K1 K2

D4 D5 D6

D7 D8 D9

D10 D11 D12

S1 M1 E2

R

S

O

H

M

S

O

H

9 Columns

9 R

ow

s

Reserved for national use

Media dependent bytes


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A1, A2 Bytes

Framing Alignment Bytes: A1, A2

To identify the initial location of a frame

A1=F6 H, A2=28 H

OOF is reported

OOF lasts for 3 m seconds

LOF is reported

A1, A2 cannot be detected for five consecutive frames;


prohibited.

34

J0 Byte

Regenerator Section Trace Byte: J0

As 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.


prohibited.

35

F1 Byte

User Channel Byte: F1

Provides a 64 kb/s data/voice channel for special

maintenance purposes.


prohibited.

36

D1-D12 Bytes

Data Communication Channel (DCC) Bytes: D1-D12

DCC is the channel for transmission of OAM information

between NEs and NMS.

192kbp/s (3 x 64 = 192) channel is defined using bytes D1, D2,

and D3 as a Regenerator Section DCC.

576kbp/s (9 x 64 = 576) channel is defined using bytes D4 to D12

as Multiplex Section DCC.


prohibited.

37

E1, E2 Bytes

Orderwire 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


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38

B1 Byte

Bit 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-Nframe.

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.


prohibited.

39

B1 Byte

B1 Byte Principle

At the 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 ofthe preceding frame.

At the receiving end, the BIP-8 is computed over all bits of theregenerator after de-scrambling. This result is then Exclusive OR withthe 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.


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40

B1 Byte

At the transmitting side (A), BIP-8 is computed over all bits of the

first frame, and result is placed in byte B1 of the second frame. At

the receiving end (B), 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.

1st

frame

A B

1st frame

Transmitting end

2nd

frameNth

frame

Nth

frame

2nd

frame

Receiving end


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41

B2 Bytes

Bit Interleaved Parity Nx24 (BIP-Nx24) byte: B2

B2 is for multiplex section error monitoring.

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 partition: 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 partition of the signal.


prohibited.

42

B2 Bytes

B2 Byte Principle

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

At receiving end, BIP- Nx24 is computed over all bits of the frameexcept for the first three rows of SOH, and then Exclusive OR with theB2 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


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43

M1 Byte

MS Remote Error Indication (MS-REI) Byte: M1

A return information from the receiving end detecting MS-BBE

to the transmitting end.

Convey the count of interleaved bit blocks that have been

detected in error by B2 bytes in the receiving end.

The transmitting end will report a corresponding performance

event, MS-REI.


prohibited.

44

K1, K2 Bytes

Automatic 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 the receiving end.

110 indicates MS-RDI alarm (Multiplex Section Remote Defect

Indication) at the transmitting end.


prohibited.

45

S1 Byte

Synchronization 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 clock. The smaller the value indicates better quality

of the clock sources.


prohibited.

46

Section Overhead

Byte interleaving of Section Overhead

When STM-1 frames are multiplexed into STM-N, the byte

interleave multiplexing method used for AU Pointer and

Payload is different from Section Overhead. In the former case,

all bytes are interleaved. For the latter, 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, B1, B2, J0 etc.


prohibited.

47

Path Overhead

Classifications

High Order Path Overhead (HPOH)

Low Order Path Overhead (LPOH)


prohibited.

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HPOH

Path trace byteJ1

B3

C2

G1

F2

H4

F3

K3

N1

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


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49

J1 Byte

Path Trace Byte: J1

The first byte of VC4

Pointed by AU-PTR

Required to be matched at transmitting and receiving ends


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50

B3 Byte

Path BIP-8 Code Byte: B3

Implements higher order VC’s error monitoring

Monitoring principle: BIP-8 even parity

The value of B3 byte needs to be compared at bothtransmitting and receiving ends. Any inconsistency betweentwo results means transmission errors in VC-4.


prohibited.

51

C2 Byte

Signal Label Byte: C2

Indicates the composition and type of multiplexing structure

Examples:

00H means unused

02H means multiplexing structure is 3xTUG-3

Indicate the information about payload type

Required match at both ends


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52

G1 Byte

Path Status Byte: G1

Indicating high order VC transmission status

Return message from receiving end to transmitting end

HP-REI: Higher Order Path Remote Error indication (sum of

receiving error block of VC4)

HP-RDI: High Order Path Remote Defect Indication


prohibited.

53

H4 Byte

Multi-frame Indicator Byte: H4

Indicate 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


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54

Low Order Path Overhead

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

J2: Low-order Path Trace Byte

N2: Byte for network operator use

K4: APS for low order path

1

1

9

500us VC12 Multi-frame

V5 J2 N2

VC12 VC12VC12

4

K4

VC12


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V5 Byte

Path 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 status

Error block monitoring: b1-b2

Return path status message: b3, b8

Signal label: b5-b7

Similar with B3, C2, and G1


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56

SDH Frame Structure

Understanding 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.


prohibited.

57

SDH Frame Structure

Comparison

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)


prohibited.

58

Hierarchy 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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(18) SDH Basic Concepts