SDH Principle
Chapter1 SDH Overview
Chapter2 Frame Structure & Multiplexing Methods
Chapter3 Overhead & Pointers
Emergence of SDH
What is SDH?
---- Synchronous Digital Hierarchy
---- It defines frame structure, multiplexing metho
d, digital rates hierarchy and interface code patte
rn.
Why did SDH emerge?
---- Need for a system to process increa
sing amounts of information.
---- New standard that allows mixing equ
ipment from different suppliers.
Advantages of SDH ( Interfaces )
PDH SDH
Electrical interfaces Electrical interfaces
--- Only regional standards. 3 PDH r --- Can be connected with existin
ate hierarchies for PDH: European (2.0 g PDH signals.
48 Mb/s), Japanese, North American (1.
544 Mb/s).
Optical interfaces
Optical interfaces
--- Can be connected to multiple
--- No standards for optical line equi vendors’ optical transmission equipment
pments, manufacturers develop at their s.
will.
Disadvantages of PDH (Multiplexing methods )
PDH : Asynchronous Multiplexing
The location of low-rate signals in high-rate signals is neither regular nor predictabl
e.
140 Mb/s 140 Mb/s
34 Mb/s 34 Mb/s
8 Mb/s 8 Mb/s
de-multiplexer multiplexer
de-multiplexer multiplexer
de-multiplexer multiplexer
2 Mb/s level by level
Not suitable for huge-volume transmission
Advantages of SDH (Multiplexing methods )
byte interleaved multiplexing method
Low rate SDH to higher rate SDH One Byte from
A STM-1 B
A A
( STM-1→STM-4→STM-16→STM-64 )
B …
B B 4:1
STM-4
C
C
--- Synchronous multiplexing method and fl
D exible mapping structure
D --- Use multistage pointer to align PDH lo
What about PDH? ads in SDH frame, thus, dynamic drop-and
-insert capabilities
Advantages of SDH (OAM function )
PDH SDH
Weak Operation, Admi Abundant overheads by
nistration & Maintenan tes for operation, admin
ce function. istration and maintenan
ce.
About 5% of the total b
ytes are being used
Advantages of SDH ( Compatibility )
PDH, SDH, AT
M, Ethernet
packing
package STM-N SDH STM-N package
network
transmit receive Processing
Processing
unpacking
PDH, SDH,
ATM, Ethernet
Chapter1 SDH Overview
Chapter2 Frame Structure & Multiplexing Methods
Chapter3 Overhead & Pointers
SDH Frame Structure
Frame = 125 us
From ITU-T G.707:
1. One frame lasts for 125 mic
123456789
roseconds (8000 frames/s)
2. Rectangular block structur
e 9 rows and 270 columns
(STM-1)
9 rows
3. Each unit is one byte (8 bits)
4. Transmission mode: Byte b
y byte, row by row, from lef
t to right, from top to botto
m
270 Columns
Bit rate of STM-1= 9*270*8*8000
SDH Frame Structure
Frame = 125 us
Three parts:
123456789
SOH
RSOH
− RSOH
− MSOH AU-PTR Information Payloa
9 rows
d
AU-Pointer
MSOH
Information Payload
270 Columns
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
LPOH, TU-PTR
RSOH
package
AU-PTR
HPOH
9 rows Payload low rate signal
MSOH
package
LPOH, TU-PTR
9 1 Data pac
kage
270 Columns
SDH Frame Structure
Section Overhead
Functions : Fulfills the section layer OAM
Types of Section Overhead
123
RSOH
1. RSOH monitors the regenerator
56789
AU-PTR Information Payloa section
9 rows 2. MSOH monitors the multiplexin
d
g section
MSOH Location:
1. RSOH: rows #1 ~ #3,
columns #1 ~ #9
2. MSOH: rows #5 ~ #9,
9
columns #1 ~ #9
270 Columns
SDH Frame Structure
AU-PTR
RSOH
Function:
Indicates the first byte of VC4
4 AU-PTR Information Payloa
9 rows
Location: d
row #4, columns #1 ~ #9
MSOH
J1
270 Columns
SDH Multiplexing Method
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
Go to glossary
SDH Multiplexing Structure
×1 ×1 AU-4-64c VC-4-64c C-4-64c
STM-64 AUG-64
×4
×1 ×1
STM-16 AUG-16 AU-4-16c VC-4-16c C-4-16c
×4
×1 ×1
STM-4 AUG-4 AU-4-4c VC-4-4c C-4-4c
×4
×1
×1
STM-1 AUG-1 AU-4 VC-4 C-4 E4 signal
×3
Mapping ×1
TUG-3 TU-3 VC-3 C-3 E3 signal
Aligning
×7
Multiplexing
TUG-2
Go to glossary TU-12 VC-12 C-12 E1 signal
×3
SDH Tributary Multiplexing (140M)
140 Mbit/s to STM-N
C4 VC4
1
1
H
Rate adaptatio Add HPOH Next
140M P
n page
O
H
9 Mapping 9
1 260 261
1
125 μs 125μs
SDH Tributary Multiplexing (140M)
AUG-1 1 STM-1 270
10 270
RSOH
Add Add Info
AU-PTR AU-4
AU-PTR AU-PTR Payload
×1 SOH
MSOH
9
Aligning Multiplexing
1 STM-N
AUG-N 270X N
One STM-1 frame can load only one 140Mbit/s Add
Signal SOH
9
SDH Tributary Multiplexing (34M)
34 Mbit/s to STM-N
C3 VC3
1 1
L
34M Rate Adaptati Add LPOH P Next
on page
O
H
9 9
1 84 Mapping 1 85
125μs 125μs
SDH Tributary Multiplexing (34M)
TU-3 TUG-3 VC-4
1 86 1 86 1 3 261
1 1 1
H1 H1
H2 H2
H3 H3 P
Fill
1st ×3 O R
gap R
align H
R
9 9 9
Aligning Multiplexing Same pro
cedure
as 140M
SDH Tributary Multiplexing (2M)
2 Mbit/s to STM-N
VC12 TU12
C12
1 4 1 LPOH 4 1 4
1 1 1
Next
2M Rate Adapta Add LP Add
tion OH TU-PTR page
9 9 9
125μs Mapping Aligning TU-PTR
SDH Tributary Multiplexing (2M)
TUG-2 TUG-3
1 12 1 86
1 1
R R
×3 ×7
9 9
Same proced
Multiplexing Multiplexing
ure
as 34M
Questions
What are the main parts of SDH Frame structure?
What is the transmission rate of STM-4?How to calculate?
Glossary
Mapping - A process used when tributaries are adapted into VCs by addi
ng POH information
Aligning - This process takes place when a pointer is included in a Tribut
ary 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 sign
als are adapted into a Multiplexing Section
Back
Glossary
C = Container
VC = Virtual Container
TU = Tributary Unit
AU = Administrative Unit
TUG = Tributary Unit Group
AUG = Administrative Unit Group
STM = Synchronous Transfer Module
POH = Path Overhead
Back
Chapter1 SDH Overview
Chapter2 Frame Structure & Multiplexing Methods
Chapter3 Overhead & Pointers
Section Overheads
R A1 A1 A1 A2 A2 A2 J0
S
O B1 ∆ ∆ E1 ∆ F1
H
D1 ∆ ∆ D2 ∆ D3
AU-PTR
B2 B2 B2 K1 K2
M D4 D5 D6
S
O D7 D8 D9
H
D10 D11 D12
S1 M1 E2
STM-1 ∆ = Media dependent bytes
A1 and A2 Bytes
Framing Bytes – Indicate the beginning of the STM-N frame
A1 = f6H (11110110), A2 = 28H (00101000)
In STM-N: (3XN) A1 bytes, (3XN) A2 bytes
STM-N STM-N STM-N STM-N STM-N STM-N
Finding frame head
A1 and A2 Bytes
Framing
N
Find
over 625us
A1,A2
OOF
Y
over 3ms
LOF
Next AIS
process
D1 ~ D12 Bytes
Data Communications Channels (DCC) Bytes
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: Operation, Administration and mai
ntenance
E1 and E2 Bytes
Orderwire Bytes
E1 – RS Orderwire Byte – RSOH orderwire message
E2 – MS Orderwire Byte – MSOH orderwire message
NE NE NE NE
E1 and E2
Digital telephone channel
E1-RS, E2-MS
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)
B1 STM-N B1 STM-N
Tx Rx
A1 00110011
A2 11001100
A3 10101010
BIP-8 Calculate 2#STM-N
A4 00001111 1#STM-N
BIP-8= A
B 01011010 Calculate
2#STM-N B1=A 1#STM-N
BIP-8=A1
Verify A1&A→B1 BBE
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 mechanism of B2 is same as B1
M1 Byte
Multiplexing Section Remote Error Indication Byte
A return message from Rx to Tx ,when Rx find B2 bit errors
A count of BIP-24xN (B2) bit errors
Tx generate corresponding performance event MS-FEBBE
Traffic
Tx Rx
Return M1
Generate
MS-FEBBE Find B2 bit errors
MS-REI Generate MS-BBE
K1 and K2 (b1-b5)
Automatic Protection S
witching (APS) bytes
Transmitting APS protocol
Used for network multiplexing
protection switch function
K2 (b6 ~ b8) Start
Rx detects K2 (b6-b8)="1
11“ Detect
Generate MS-AIS ala K2 (b6-b8 110
)
rm
Rx detects K2 (b6-b8)="1
111
10"
Generate
Generate MS-RDI ala MS-AIS
rm
Return Generate
MS-RDI MS-RDI
S1 Byte
Synchronization Status Message Byte (SSMB): S1
(b5~ b8)
Value indicates the sync. level
bit 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).
Path Overheads
1 2 3 4 5 6 7 8 9 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 Indi
F3 Path User Channel
K3 AP Switching
N1 Network Operator
Higher Order Path Overhead
Path trace byte: J1
Detect J1
> The first byte of VC-4
> User-programmable
> The received J1 should mat
ch with the expected J1 N Y
Match
Next proce
HP-TIM ss
B3 Byte
Path bit parity
code byte (even parity code) Verify B3
Used to detect bit errors
Mechanism is same as B1and B2
N Y
correct
HP-BBE Next proc
ess
Signal label byte: C2
Detect C2
> Specifies the mapping type in
the VC-n
> 00 H Unequipped N Y
00H
02 H TUG structure
Y N
13 H ATM mapping Match HP-UNEQ
The received C2 should mat
ch with the expected C2
Next pro HP-SLM
cess
Insert AIS do
wnward
Path Overheads
Low Order Path Overhead
1 4
1 V5 J2 N2 K4
VC-12 VC-12 VC-12 VC-12
9
500μs VC-12 multiframe
Path Overhead Bytes
V5
> First byte of the multiframe
> Indicated by TU-PTR
Functions: Error checking, Signal Label and Path Status of VC-12
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)
Pointers
Pointers
AU-PTR TU-PTR
AU-PTR
1 RSOH Negative Positive
justification justification
4 H1YYH2FF H3H3H3 0¡ ª ¡ ª 1¡ ª ¡ ª ------ 86¡ ª ¡ ª
MSOH
9 435¡ ª ¡ ª 436¡ ª ¡ ª------ 521¡ ª ¡ ª 125us
1 522¡ ª ¡ ª 523¡ ª ¡ ª -----608¡ ª ¡ ª
RSOH
696¡ ª ¡ ª 697¡ ª ¡ ª ------782¡ ª ¡ ª
4 H1YYH2FFH3H3H3 0¡ ª ¡ ª 1¡ ª ¡ ª ------ 86¡ ª ¡ ª
MSOH
9 250us
1 9 270
TU-PTR
1 4
1
VC-12 VC-12 VC-12 VC-12
9 V1 V2 V3 V4
500μs VC-12 multiframe
TU POINTERS
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?
Summary SDH Overview
SDH Frame Structure & Multiplexing
Methods
Overhead & Pointers
