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SDH Frame Structure
SDH
Engr. Mian Shahzad IqbalLecturerDepartment of TelecommunicationEngineering
SDH Multiplexing Method
Synchronous Digital Hierocracy
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Understand the basic of SDH standards
Know the features, applications and advantages of SDH
Objectives
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What is SDH?---- Synchronous Digital Hierarchy---- It defines frame structure, multiplexing method, digital rates hierarchy and interface code pattern.
Emergence of SDH
Why did SDH emerge?---- Need for a system to process increasing amounts of information.---- New standard that allows mixing equipment from different suppliers.
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Advantages of SDH ( Interfaces )
PDH Electrical interfaces
--- Only regional standards. 3 PDH rate hierarchies for PDH: European (2.048 Mb/s), Japanese, North American (1.544 Mb/s).Optical interfaces--- No standards for optical line equipments, manufacturers develop at their will.
SDHElectrical interfaces
--- Can be connected with existing PDH signals.
Optical interfaces--- Can be connected to multiple vendors’ optical transmission equipments.
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Disadvantages of PDH (Multiplexing methods )
PDH : Asynchronous MultiplexingThe location of low-rate signals in high-rate signals is neither regular nor predictable.
140 Mb/s34 Mb/s
8 Mb/s
34 Mb/s
8 Mb/s
2 Mb/s
140 Mb/s
multiplexer
multiplexer
multiplexerde-multiplexer
de-multiplexer
de-multiplexer
level by levelNot suitable for huge-volume transmission
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Advantages of SDH (Multiplexing methods )byte interleaved multiplexing method
Low rate SDH to higher rate SDH( STM-1→STM-4→STM-16→STM-64 )
4:1
STM-1A
STM-1B
STM-1C
STM-1D
A
B
D
C
B
A
D
C
B
A
…STM-4
One Byte from STM-1 B
--- Synchronous multiplexing method and flexible mapping structure
--- Use multistage pointer to align PDH loads in SDH frame, thus, dynamic drop-and-insert capabilities
What about PDH?
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Advantages of SDH
PDH
Weak Operation, Administration & Maintenance function.
SDH
Abundant overheads bytes for operation, administration and maintenance.
About 5% of the total bytes are being used
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Advantages of SDH ( Compatibility )
package
transmit
SDHnetwork
unpacking
PDH, SDH, ATM, Ethernet
packing
STM-N STM-N package
receive ProcessingProcessing
PDH, SDH, ATM, Ethernet
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Comparison between SDH and PDH
Low bandwidth utilization ratio.
64 E1139.264 Mbit/sE416 E134.368 Mbit/sE3
128 E08.448 Mbit/sE232 E02.048 Mbit/sE1
One 64 kbit/s64 kbit/sE0ChannelsDigital Bit RateSignal
4032 E1, 192 E3, 64 E4STM-6410 Gbit/s9953.28Mbit/s1008 E1, 48 E3 or 16 E4STM-162.5 Gbit/s2488.32Mbit/s252 E1, 12 E3 or 4 E4STM-4622 Mbit/s622.08 Mbit/s63 E1, 3 E3 or 1 E4STM-1155 Mbit/s155.52 Mbit/sSDH CapacitySDHAbbreviatedBit Rate
PDH Hierarchy
SDH Hierarchy
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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(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
Bit rate of STM-1= 9*270*8*8000
123456789
270 Columns
9 rows
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SDH Frame Structure
Three parts
Frame = 125 us
9
MSOH
AU-PTR Information
Payload
RSOH123456789
270 Columns
9 rows
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SDH Frame StructureInformation 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-PTR Payload
RSOH
270 C l
HP
OH
1
package
package
low rate signal
LPOH, TU-PTR
LPOH, TU-PTR
9 rows
Data packag
e
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SDH Frame Structure
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 ~ #92. MSOH: rows #5 ~ #9,
columns #1 ~ #9
123
56789
MSOH
AU-PTR Information
Payload
RSOH
Section OverheadSection 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
J1
AUAU--PTRPTR
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SDH Multiplexing MethodSDH 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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SDH Tributary Multiplexing (140M)
140 Mbit/s to STM-N
140M Rate adaptation
Add HPOH
C4
9
1 260125 μs
1
Next page
Mapping
VC4
1
9
125μs1 261
HPOH
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SDH Tributary Multiplexing (140M)
AddAU-PTR
AddSOH
Aligning
AU-PTR AU-4
10 270
×1
AUG-1
MultiplexingAUG-N
1 270
RSOH
MSOH
InfoPayloadAU-PTR
9
STM-1
270X N1
9
STM-N
AddSOH
One STM-1 frame can load only one 140Mbit/s Signal
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SDH Tributary Multiplexing (34M)
34 Mbit/s to STM-N
34M Rate Adaptation
Add LPOH
C3
1 849
125μs
1 1
9
VC3
LPOH
125μs1 85
Next page
Mapping
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SDH Tributary Multiplexing (34M)
1st align
Fillgap
×3
86
TU-3
1
H1H2H3
1
9
1 86
Aligning
1
9
H1H2H3
R
TUG-3
Multiplexing
POH
R R
VC-4
9
11 2613
Same procedureas 140M
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SDH Tributary Multiplexing (2M)
2 Mbit/s to STM-N
2M Nextpage
125μs
1 4
C12
1
9
LPOH
VC121 4
1
9
RateAdaptation
Add LPOH
Add TU-PTR
Mapping Aligning
TU12
1 41
9
TU-PTR
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SDH Tributary Multiplexing (2M)
×3
1 12
TUG-2
1
9
×7
Multiplexing
R R
TUG-3
1 86
1
9
Multiplexing Same procedureas 34M
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Glossary► Mapping - A process used when
tributaries are adapted into VCs by adding POH information
► Aligning - This process takes place when a pointer is included in a Tributary 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 signals are adapted into a Multiplexing Section
Back
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GlossaryC = ContainerVC = Virtual ContainerTU = Tributary UnitAU = Administrative UnitTUG = Tributary Unit GroupAUG = Administrative Unit GroupSTM = Synchronous Transfer ModulePOH = Path Overhead Back
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1. SDH Overview
2 . Frame Structure & Multiplexing
Methods
3. Overhead & Pointers
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Section Overheads
A1 A1 A1 A2 A2 A2 J0B1 ∆ ∆ E1 ∆ F1D1 ∆ ∆ D2 ∆ D3
AU-PTRB2 B2 B2 K1 K2D4
D5
D6D
7D8
D9D
10D11
D12S1 M
1E2
RSOH
MSOH
∆ = Media dependent bytesSTM-1
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Questions