SDH Principle 20080528 A

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Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved.

SDH Principle

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Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved. Page1

Contents

1. SDH Overview

2. Frame Structure & Multiplexing Methods

3. Overheads & Pointers

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Emergence of SDH

What is SDH?

Synchronous Digital Hierarchy

It defines a standard frame structure, a specific

multiplexing method, and so on.

Why did SDH emerge?

Need for a system to process increasing amounts of

information.

New standard that allows interconnecting equipment

of different suppliers.

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Advantages of SDH

Interfaces

PDH electrical interfaces

Only 3 regional standards:

European (2.048 Mb/s),

Japanese, North American

(1.544 Mb/s)

PDH optical interfaces

No standards,

manufacturers develop at

their will.

SDH electrical interfaces

Universal standards

SDH optical interfaces

Can be connected to

different vendorsoptical

transmission equipments.

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140 Mb/s

34 Mb/s 34 Mb/s

8 Mb/s 8 Mb/s

2 Mb/s

140 Mb/s

Not suitable for huge-volume transmission

Headache for network planners

More equipment to achieve this functionality

More equipment More floor space

More power More costs

Demultiplexers Multiplexers

Multiplexing methods: Level by level

Disadvantages of PDH

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Advantages of SDH

Lower rate SDH to higher rate SDH

(STM-1 STM-4 STM-16STM-64)

4:1

STM-1

A

STM-1

B

STM-1

C

STM-1

D

A

B

D

C

B

A

D

C

B

A

STM-4

One Byte from

STM-1 B

--- Synchronous multiplexing method andflexible mapping structure

--- Multistage pointer to align PDH loads in

SDH frame, thus, dynamic drop-and-insert

capabilitiesWhat about PDH?

Multiplexing methods: byte interleaved

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Advantages of SDH

OAM function

PDH

In the frame structure of

PDH signals, there are

few overhead bytes used

for OAM.

Weak OAM function

SDH

Abundant overheads

bytes for OAM

Remote & Centralized

Management

Fast circuit provisioning

from centralized point

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Advantages of SDH

Processing

PDH ATMSDH Ethernet

Pack

SDH NetworkProcessing

PDH ATMSDH Ethernet

Transmit Receive

Container

STM-NSTM-N

Container

Service Signal Flow Model

Unpack

Compatibility

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Comparison between SDH and PDH

Low bandwidth utilization ratio

In PDH, E4 signal (140Mbits/s) can contain 64 E1 signals.

In SDH, STM-1 (155 Mbits/s) can only carry 63 E1 signals.

Complex mechanism of pointer justification

Influence of excessive use of software on system security

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Contents

1. SDH Overview



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SDH Frame Structure

From ITU-T G.707:

1. One frame lasts for 125

microseconds (8000

frames/s)

2. Rectangular blockstructure 9 rows and 270

columns (Basic frame:

STM-1)

3. Each unit is one byte (8 bits)

4. Transmission mode: Byte

by byte, row by row, from

left to right, from top to

bottom

Bit rate of STM-1= 9*270*8*8000

1

23

4

5

6

7

89

270 Columns

9 rows

Frame = 125 us

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SDH Frame Structure

Frame = 125 us

9

MSOH

AU-

PTRInformation

Payload

RSOH

1

23

4

5

6

7

8

9

270 Columns

9 rows

Three parts:

SOH

AU-Pointer

InformationPayload

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SDH Frame Structure

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

9

MSOH

AU-PTRPayload

RSOH

270 Columns

HPOH

1

package

package

low rate signal

LPOH, TU-PTR

LPOH, TU-PTR

9 rows

Data

package

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SDH Frame Structure

Functions: Fulfills the section layer OAM

9

270 Columns

9 rows

Types of Section Overhead

1. RSOH monitors the regenerator

section

2. MSOH monitors the

multiplexing section

Location:

1. RSOH: rows #1 ~ #3,columns #1 ~ #9

2. MSOH: rows #5 ~ #9,

columns #1 ~ #9

1

2

3

5

6

7

89

MSOH

AU-PTR Information

Payload

RSOH

Section Overhead

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SDH Frame Structure

9

MSOH

AU-PTR Information

Payload

RSOH

270 Columns

9 rows4

Function:

Indicates the first byte of VC4

Location:

row #4, columns #1 ~ #9

J

1

AU-PTR

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SDH Multiplexing Features

SDH Multiplexing includes:

Low to high rate SDH signals (STM-1STM-N)

PDH to SDH signals (2M, 34M & 140M STM-N)

Other hierarchy signals to SDH Signals (IPSTM-N)

Some terms and definitions:

Mapping

Aligning

MultiplexingGo to glossary

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AU-4

TU-3TUG-3 VC-3 C-3

VC-4 C-4

TU-12 VC-12 C-12

TUG-2

3

1

7

3

E4

signal

E3 signal

E1 signal

Multiplexing

Mapping

Aligning

STM-1 AUG-11 1

AUG-4

AUG-16

AUG-64

STM-4

STM-16

STM-64

1

1

1

4

4

4

Go to glossary

C-4-4cVC-4-4cAU-4-4c1

C-4-16cVC-4-16cAU-4-16c1

C-4-64cVC-4-64cAU-4-64c1

SDH Multiplexing Structure

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From 140Mb/s to STM-N

140MRate

adaptationAdd HPOH

C4

9

1 260

125 s

1

Next

Mapping

VC4

1

9

125s1 261

H

P

O

H

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Add

AU-PTRAdd

SOH

Aligning

AU-PTR AU-4

10 270

X1

AUG-1

Multiplexing

AUG-N

1 270

RSOH

MSOH

Info

PayloadAU-PTR

9

STM-1

Add

SOH

One STM-1 frame can load

only one 140Mbit/s Signal

1 270N

RSOH

MSOH

Info

PayloadAU-PTR

9

STM-N

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34M Rate

AdaptationAdd LPOH

C3

1 84

9

125s

1 1

9

VC3

L

P

O

H

125s1 85

Next

Mapping

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1st

align

Fill

gap3

86

TU-3

1

H1

H2H3

1

9

1 86

1

9

H1

H2H3

R

TUG-3

Multiplexing

H

P

O

H

R R

VC-4

9

1

1 2613

Same

procedure

as 140M

Aligning

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From 2Mb/s to STM-N

2MNext

page

125s

1 4

C12

1

9

4LPOH

VC12

1

1

9

Rate

AdaptationAdd

LPOHAdd

TU-PTR

Aligning

TU12

1 4

1

9

TU-PTRMapping

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From 2Mb/s to STM-N

X 3

1 12

TUG-2

1

9

X 7

Multiplexing

R R

TUG-3

1 86

1

9

MultiplexingSame

procedure

as 34M

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Questions

What are the main parts of SDH Frame structure?

What is the transmission rate of STM-4? How to

calculate it ?

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Contents

1. SDH Overview



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Overheads

Overheads

Section

Overhead

(SOH)

Path

Overhead

(POH)

Regenerator

Section Overhead

(RSOH)

Multiplex Section

Overhead

(MSOH)

High Order Path

Overhead

(HPOH)

Low Order Path

Overhead

(LPOH)

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Overheads

A1 A1 A1 A2 A2 A2 J0 X X

B1 E1 F1 X X

D1 D2 D3

AU-PTR

B2 B2 B2 K1 K2

D4 D5 D6

D7 D8 D9

D10 D11 D12

S1 M1 E2

HPOH:VC-3/4

J1

B3

C2

G1

F2

H4

F3

K3

N1

RSOH

MSOH

1 2 3 4 5 6 7 8 9 10

1

2

3

45

6

7

8

9

Media dependent bytes (Radio-link, Satellite)

X Reserved for National use

Huawei propriety bytes LPOH: VC-11/12

V5 J2 N2 K4

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A1 and A2 Bytes

Framing Bytes

Indicate the beginning of the STM-N frame

Bytes are unscrambled

A1 = f6H (11110110), A2 = 28H (00101000)

STM-N: (3XN) A1 bytes, (3XN) A2 bytesSTM-N STM-N STM-N STM-N STM-N STM-N

Finding frame head

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A1 and A2 BytesFrame

Next

process

Find

A1,A2

OOF

LOF

N

Y

AIS

over 3ms

over 625s(5 frames)

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D1 ~ D12 Bytes

Data Communications Channel (DCC) Bytes

RS-DCCD1 ~ D3192 Kbit/s (3x64 Kbit/s)

MS-DCCD4 ~ D12576 Kbit/s (9x64 Kbit/s)

TMN

DCC channel

NE NE NENE

OAM Information: Operation, Administration and

maintenance

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E1 and E2 Bytes

Orderwire Bytes

E1RS Orderwire Byte Used between regenerators

E2MS Orderwire Byte Used between multiplexers

Digital telephone channel

E1-RS, E2-MS

E1 and E2

NE NE NENE

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B1 Byte

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 (performance event)

Tx

2#STM-N

Rx

1#STM-N Calculate B

1#STM-N

2#STM-N

Calculate B

A1 00110011

A2 11001100A3 10101010

A4 00001111

B 01011010

BIP-8

B1 = B

STM-NB1

B

Compare B& B RS-BBE

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B2 Byte

Bit interleaved Parity Code (MS BIP-24) Byte

BIP-24 is used to check the bit errors over the MS

B2 BBE is represented by MS-BBE (performance event)

The working mechanism of B2 is same as B1

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M1 Byte

Multiplexing Section Remote Error Indication Byte A return message from Rx to Tx ,when Rx find B2 bit errors

Value is the same as the count of BIP-24xN (B2) bit errors

Tx generate corresponding performance event MS-FEBBE

Tx Rx

Traffic

Generate

MS-FEBBE

MS-REI

Find B2 bit errors

Generate MS-BBE

Return M1

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K1 and K2 (b1-b5) Bytes

Automatic

Protection

Switching

(APS) bytes

Transmitting APS protocolUsed for network multiplexing

protection switch function

P

WTR

WTR P

I

I

I I

P

S

S P

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K2 (b6 ~ b8) Byte

Rx detects K2 (b6-b8) = "111

Generate MS-AIS alarm

Rx detects K2 (b6-b8) = "110"

Generate MS-RDI alarm

Generate

MS-AIS

Start

Detect

K2 (b6-

b8)

Return

MS-RDI

Generate

MS-RDI

111

110

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S1 Byte

Synchronization Status Message Byte (SSB): S1

b1 ~ b4Value indicates the external clock ID (Extended SSM)

b5 ~ b8Value indicates the sync. Level (Standard SSM)

bits 5 ~ 8 Description

0000 Quality unknown (existing sync. Network)

0010 G.811 PRC

0100 SSU-A (G.812 transit)

1000 SSU-B (G.812 local)

1011 G.813 (Sync. Equipment Timing Clock)

1111 Do not use for sync (DNU).

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Path Overheads

J1

B3

C2

G1

F2

H4

F3

K3

N1

VC-n Path Trace Byte

Path BIP-8

Path Signal Label

Path StatusPath User Channel

TU Multiframe Indication

Path User Channel

AP Switching

Network Operator

Higher Order Path Overhead

1 2 3 4 5 6 7 8 9 10

1

2

3

45

6

7

89

R S O H

M S O H

A U

P T R

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J1 Byte

Next

process

Detect J1

Match

HP-TIM

YN

Path trace byte

The first byte of VC-4

User-programmable (HUAWEI

SBS) The received J1 should match

the expected J1

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B3 Byte

Next

process

VerifyB3

YNCorrect

HP-BBE

Path bit parity

Even parity code

Used to detect bit errors

Mechanism is same as B1 and B2

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C2 Byte

Detect C2

00H

HP-UNEQMatch

HP-SLMNext

process

Insert AIS

downward

N Y

NY

Signal label byte

The received C2 should

match with the expected C2

Specifies the mapping type inthe VC-n

00 HUnequipped

02 HTUG structure

13 H ATM mapping

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VC-12VC-12VC-12VC-12

K4N2J2V51

9

1 4

500s VC-12 multi-frame

Low Order Path Overhead V5

Indicated by TU-PTR

Error checking, Signal Label

and Path Status of VC-12 b1 - b2Error Performance

Monitoring (BIP-2)

b3Return Error detected in

VC-12 (LP-REI)

b8Return alarm detected

in VC-12 (LP-RDI)

Path Overheads

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Pointers

Pointers

Administrative

Unit Pointer

(AU-PTR)

Tributary

Unit Pointer

(TU-PTR)

Bytes indicated

AU-PTR VC-4 J1

TU-PTR VC-3 J1

VC-12V5

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AU-PTR

RSOH

MSOH

MSOH

RSOH

H1YYH2FF H3H3H3

H1YYH2FFH3H3H3

0 --- 1--- --- --- --- --- --- --- --- --- --- 86

696 --- 697 --- --- --- --- --- --- --- --- 782

1 9 270

1

4

9

1

4

9

125s

250s

522 --- 523 --- --- --- --- --- --- --- --- 608

435 --- 436 --- --- --- --- --- --- --- --- 521

Negativejustification

Positivejustification

0 --- 1 --- --- --- --- --- --- --- --- --- --- 86

435 --- 436 --- --- --- --- --- --- --- --- 521

87 --- 88 --- --- --- --- --- --- --- --- --- 173

87 --- 88 --- --- --- --- --- --- --- --- --- 173

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TU-PTR

VC3

H1

H2

H3

TU POINTERS

VC-

12

VC-

12

VC-

12

VC-

12

V1 V2 V3 V4

1 4

1

9

TU POINTERS

TU Multi-frame 500s

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Questions

Which byte is used to report the MS-AIS and

MS-RDI?

What is the mechanism for R-LOF generation?

Which byte implements the RS (MS/HP) error

monitoring?

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Summary

SDH Overview

Frame Structure & Multiplexing Methods

Overheads & Pointers

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SDH Principle 20080528 A

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