SDH Principle
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Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Objectives

Upon completion of this course, you will be able to:

Understand the basic of SDH multiplexing standard

Know the features, applications and advantages of SDH based
equipment
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page1
Contents
1. SDH Overview
2. Frame Structure & Multiplexing Methods
3. Overheads & Pointers
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page2
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 a system to process increasing amounts of information

Need a new standard that allows interconnecting equipment of
different suppliers
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page3
Advantages of SDH

Interfaces

PDH electrical interfaces


Only 3 regional standards:
European (2.048 Mb/s),
SDH electrical interfaces


SDH optical interfaces
Japanese, North American
(1.544 Mb/s)


PDH optical interfaces

Universal standards
Can be connected to different
vendors’ optical transmission
equipments
No standards, manufacturers
develop at their will
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page4
Disadvantages of PDH

Multiplexing methods: Level by level
140 Mb/s
140 Mb/s
34 Mb/s
34 Mb/s
8 Mb/s
8 Mb/s
Multiplexers
Demultiplexers
2 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
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page5
Advantages of SDH
Multiplexing methods: byte interleaved

STM-1A
AA
Lower rate SDH to higher rate SDH
(STM-1 STM-4 STM-16  STM-64)
A
…
STM-1B
BB
One Byte from
STM-1 B
B
4:1
STM-4
STM-1C
C
C
--- Synchronous multiplexing method and
flexible mapping structure
STM-1D
D
D
What about PDH?
--- Multistage pointer to align PDH loads in
SDH frame, thus, dynamic drop-and-insert
capabilities
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page6
Advantages of SDH

OAM function

PDH


SDH
In the frame structure of

PDH signals, there are few
overhead bytes used for
for OAM

OAM.

Weak OAM function
Abundant overheads bytes
Remote & Centralized
Management

Fast circuit provisioning
from centralized point
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page7
Advantages of SDH

Compatibility
STM-N
Transmit
Receive
Processing
PDH
SDH
ATM
Processing
SDH Network
Container
Pack
STM-N
Ethernet
Container
PDH
SDH
Service Signal Flow Model
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page8
Unpack
ATM
Ethernet
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
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page9
Contents
1. SDH Overview
2. Frame Structure & Multiplexing Methods
3. Overheads & Pointers
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page10
SDH Frame Structure
From ITU-T G.707:
1. One frame lasts for 125
microseconds (8000
frames/s)
2. Rectangular block structure
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
Frame = 125 us
1
2
3
4
5
6
7
8
9
9 rows
270 Columns
Bit rate of STM-1= 9*270*8*8000
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page11
SDH Frame Structure (Cont.)

Three parts:

SOH

AU-Pointer

Information Payload
Frame = 125 us
1
2
3
4
5
6
7
8
9
RSOH
AU-PTR
Information
Payload
MSOH
9
270 Columns
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page12
9 rows
SDH Frame Structure (Cont.)
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
LPOH, TU-PTR
RSOH
package
HPOH
9 rows
AU-PTR
low rate signal
Payload
MSOH
9
package
1
270 Columns
LPOH, TU-PTR
Data
package
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page13
SDH Frame Structure (Cont.)
Section Overhead
Functions: Fulfills the section layer OAM
1
2
3
Types of Section Overhead
RSOH
1.
AU-PTR
5
6
7
8
9
Information
Payload
MSOH
9
9 rows
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
270 Columns
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page14
SDH Frame Structure (Cont.)
AU-PTR
Function:
Indicates the first byte of
VC4
RSOH
4 AU-PTR
Information
Payload
Location:
row #4, columns #1 ~ #9
MSOH
J1
9
270 Columns
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page15
9 rows
SDH Multiplexing Features


SDH Multiplexing includes:

Low to high rate SDH signals (STM-1  STM-N)

PDH to SDH signals (2M, 34M & 140M  STM-N)

Other hierarchy signals to SDH Signals (IP  STM-N)
Some terms and definitions:

Mapping

Aligning

Multiplexing
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Page16
SDH Multiplexing Structure
×1
×1 AU-4-64c
AUG-64
×4
×1 AUG-16 ×1 AU-4-16c
STM-16
×4
×1 AUG-4 ×1 AU-4-4c
STM-4
STM-64
×4
STM-1
×1
VC-4-64c
C-4-64c
VC-4-16c
C-4-16c
VC-4-4c
C-4-4c
VC-4
C-4
E4 signal
×1
AUG-1
AU-4
×3
Mapping
Aligning
Multiplexing
Go to glossary
TUG-3
×1
TU-3
VC-3
C-3
E3 signal
TU-12
VC-12
C-12
E1 signal
×7
TUG-2
×3
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Page17
From 140Mb/s to STM-N
C4
VC4
1
140M
Rate
adaptation
1
H
P
O
H
Add HPOH
Mapping
1
260
Next
9
125μs
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
9
1
125μs
Page18
261
From 140Mb/s to STM-N
10
1
AUG-1
270
STM-1
270
RSOH
Add
AU-PTR
AU-PTR
AU-4
AU-PTR
Add
SOH
X1
Info
Payload
MSOH
9
Aligning
Multiplexing
AUG-N
1 STM-N
270N
RSOH
One STM-1 frame can load
only one 140Mbit/s Signal
AU-PTR
Add
SOH
MSOH
9
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Page19
Info
Payload
From 34Mb/s to STM-N
C3
VC3
1
34M
Rate
Adaptation
1
L
P
O
H
Add LPOH
Next
9
1
84
9
Mapping
125μs
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
1
125μs
Page20
85
From 34Mb/s to STM-N
TUG-3
TU-3
1
H1
H2
H3
1
86
Fill
gap
1st
align
Aligning
1
1
9
VC-4
86
H1
H2
H3
1
1
261
H
P
R R
O
H
×3
R
9
3
9
Multiplexing
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page21
Same procedure
as 140M
From 2Mb/s to STM-N
C12
1
4
1
1
2M
Rate
Adaptation
TU12
VC12
4
LPOH
Add
LPOH
1
1
4
1
LPOH
Add
TU-PTR
Next
page
TU-PTR
125μs
9
9
Mapping
Aligning
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page22
9
From 2Mb/s to STM-N
TUG-3
TUG-2
1
86
1
12
1
1
X7
X3
R
R
9
Multiplexing
9
Same procedure
as 34M
Multiplexing
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page23
Questions

What are the main parts of SDH Frame structure?

What is the transmission rate of STM-4? How to calculate it ?
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page24
Contents
1. SDH Overview
2. Frame Structure & Multiplexing Methods
3. Overheads & Pointers
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page25
Overheads
Overheads
Section Overhead
(SOH)
Regenerator
Section Overhead
(RSOH)
Multiplex Section
Overhead
(MSOH)
Path Overhead
(POH)
High Order Path
Overhead
(HPOH)
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page26
Low Order Path
Overhead
(LPOH)
1
2
3
4
5
6
7
8
9
10
1
A1
A1
A1
A2
A2
A2
J0
X
X
J1
2
B1
●
●
E1
●
F1
X
X
3
D1
●
●
D2
●
D3


MSOH
C2
AU-PTR
4
5
B2
B2
6
D4

7
B2
B3
K1
K2
D5
D6
D7
D8
D9
8
D10
D11
D12
9
S1
M1
● Media dependent bytes (Radio-link, Satellite)
X Reserved for National use
 Huawei propriety bytes
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
G1
F2

H4
E2
F3
V5 J2 N2 K4
K3
LPOH: VC-11/12
Page27
N1
HPOH: VC-3/4
RSOH
Overheads (Cont.)
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 bytes
STM-N
STM-N
STM-N
STM-N
STM-N
Finding frame head
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Page28
STM-N
A1 and A2 Bytes (Cont.)
Frame
Find
A1,A2
N
Y
over 625μs (5
frames)
OOF
over 3ms
LOF
Next
process
AIS
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Page29
D1 ~ D12 Bytes

Data Communications Channel (DCC) Bytes

RS-DCC – D1 ~ D3 – 192 Kbit/s (3x64 Kbit/s)

MS-DCC – D4 ~ D12 – 576 Kbit/s (9x64 Kbit/s)
NE
NE
NE
NE
DCC channel
NMT
OAM Information: Operation, Administration and
maintenance
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page30
E1 and E2 Bytes

Orderwire Bytes

E1 – RS Orderwire Byte  Used between regenerators

E2 – MS Orderwire Byte  Used between multiplexers
NE
NE
NE
NE
E1 and E2
Digital telephone channel
E1-RS, E2-MS
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page31
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)
STM-N B1
Rx
Tx
BIP-8
A1
A2
A3
A4
00110011
11001100
10101010
00001111
B 01011010
1#STM-N
Calculate B
2#STM-N
B1 = B
2#STM-N
Calculate B’
Compare B’ & B  RS-BBE
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Page32
1#STM-N
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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Page33
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
Traffic
Rx
Tx
Generate
MS-FEBBE
MS-REI
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Return M1
Find B2 bit errors
Generate MS-BBE
Page34
K1 and K2 (b1-b5) Bytes
Automatic
Protection
Switching (APS)
bytes
I
I
I
I
S
S
P
P
WTR
WTR
Used for network multiplexing
protection switch function
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
P
P
Transmitting APS protocol
Page35
K2 (b6 ~ b8) Byte

Rx detects K2 (b6-b8) = "111“


Generate MS-AIS alarm
Tx detects K2 (b6-b8) = "110"

Start
Generate MS-RDI alarm
Detect
K2 (b6-b8)
110
111
Generate
MS-AIS
Return
MS-RDI
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Page36
Generate
MS-RDI
S1 Byte

Synchronization Status Message Byte (SSB): S1

b1 ~ b4  Value indicates the external clock ID (Extended SSM)

b5 ~ b8  Value 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).
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page37
Path Overheads
1 2
1
2
3
4
5
6
7
8
9
3 4 5 6 7 8 9
R
S
O
H
A U–P T R
M
S
O
Higher Order Path Overhead
H
10
J1
VC-n Path Trace Byte
B3
Path BIP-8
C2
Path Signal Label
G1
Path Status
F2
Path User Channel
H4
TU Multiframe Indication
F3
Path User Channel
K3
AP Switching
N1
Network Operator
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page38
J1 Byte

Path trace byte

The first byte of VC-4

User-programmable
(HUAWEI SBS)

Detect J1
N
Y
Match
The received J1 should
match the expected J1
Next
process
HP-TIM
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Page39
B3 Byte

Path bit parity

Even parity code

Used to detect bit errors

Mechanism is same as B1
Verify B3
N
Correct
Y
and B2
HP-BBE
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Next
process
Page40
C2 Byte

Detect C2
Signal label byte

The received C2 should match
with the expected C2

N
00H
Y
Specifies the mapping type in
the VC-n

00 H  Unequipped

02 H  TUG structure

13 H  ATM mapping
Y
Next
process
Match
N
HP-UNEQ
HP-SLM
Insert AIS
downward
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page41
Path Overheads

V5
Low Order Path Overhead

Indicated by TU-PTR

Error checking, Signal Label
1
4
1 V5
J2
N2
K4
and Path Status of VC-12

b1 - b2  Error Performance
VC-12
VC-12
VC-12
Monitoring (BIP-2)

b3  Return Error detected
in VC-12 (LP-REI)

b8  Return alarm detected
9
in VC-12 (LP-RDI)
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
500μs VC-12 multi-frame
Page42
VC-12
Pointers
Pointers
Bytes indicated
Administrative
Tributary
Unit Pointer
(AU-PTR)
Unit Pointer
(TU-PTR)
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
AU-PTR VC-4  J1
TU-PTR VC-3  J1
VC-12 V5
Page43
AU-PTR
1
Positive
justification justification
RSOH Negative
4
H1YYH2FF H3H3H3
0 --- 1--- --- --- --- --- --- --- --- --- --- 86
87 --- 88 --- --- --- --- --- --- --- --- --- 173
MSOH
9
435 --- 436 --- --- --- --- --- --- --- --- 521
1
522 --- 523 --- --- --- --- --- --- --- --- 608
RSOH
4
H1YYH2FFH3H3H3
125μs
696 --- 697 --- --- --- --- --- --- --- --- 782
0 --- 1 --- --- --- --- --- --- --- --- --- --- 86
87 --- 88 --- --- --- --- --- --- --- --- --- 173
MSOH
9
1
435 --- 436 --- --- --- --- --- --- --- --- 521 250μs
9
270
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Page44
TU-PTR
TU Multi-frame 500μs
4
1
1
H1
TU POINTERS
H2
H3
VC3
VC-
VC-
VC-
VC-
12
12
12
12
TU POINTERS
9
V1
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
V2
Page45
V3
V4
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?
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page46
Summary

SDH Overview

Frame Structure & Multiplexing Methods

Overheads & Pointers
Copyright © 2012 Huawei Technologies Co., Ltd. All rights reserved.
Page47
Thank you
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