INTRODUCTION PDH & SDH
On Job Training July 2006
PT Indonesia Comnets Plus
On Job Training, July 2006PT Indonesia Comnets Plus
Agenda
Pre SDH (PDH) SDH The SDH Frame Frame Structure
Overhead and Payload Analysis
Tributary Units SDH Network
Protection
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Plesiochronous Digital Hierarchy
2 Mbps
8 Mbps
34 Mbps
140 Mbps
2 Mbps
8 Mbps
34 Mbps
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Multiplexing hierarchy
The PDH high capacity transmission networks are based on a hierarchy of digital multiplexed signals: E.1 to E.4.
The basic building block is the primary rate of 2.048 Mb/s (E.1). This could be made up of 30 x 64 Kb/s voice channels. This would then be multiplexed up to a higher rate for high capacity transmisson.
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Four signals at the primary rate can be multiplexed up to the secondary rate, E.2, of 8.448 Mb/s and so on up to a rate of 139 Mb/s (E.4).
Thus the 139 Mb/s rate represents 64 x 2.048 Mb/s signals and 1920 multiplexed voice channels.
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Developing networks
The plesynchronous multiplexing technology, often called PDH (Plesiochronous Digital Hierarchy), left no room in the signal structures for network management and maintenance functions.
We are therefore left with no spare signal capacity to provide improvements in the signal transmission.
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As networks developed inter-connection became increasingly complex. It required banks of multiplexers and large, unreliable distribution frames.
It became clear that the original standards, designed for point-to-point links, were just not suitable.
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Tributary access We want to have easy access to an
individual tributary, in order that it may be re-routed.
We cannot do this without having to demultiplex the whole signal down to the required tributary level.
Costs go up as we demultiplex, and they then double because we have to re-multiplex the signal back up again.
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No commont standard
Before SDH there were no standards to ensure that equipment from different vendors interworked on the same system.
Vendors can have their own unique designs which means we have to buy the same vendor’s equipment for both ends of the line.
Ideally we would like to shop around for the most suitable equipment, without having to keep to the same supplier.
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What we need
Network operating companies have to provide faster, cost effective provisioning of customer circuits and services, as well as control of transmission bandwidth.
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SDH Definition
SDH is a standard for ‘high speed – high capacity’ optical telecommunication networks ; more spesifically a synchronous digital hierarchy.
It is a synchronous digital transport system aimed at providing a more simple, economic and flexible telecommunications network infrastructure.
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Advantages of SDH
Designed for cost effective, flexible telecoms networking – based on direct synchronous multiplexing.
Provides built-in signal capacity for advanced network management and maintenance capabilities.
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Provides flexible signal transportation capabilities – designed for existing and future signals.
Allows a single telecommunication network infrastructure – interconnects network equipment from different vendors
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Where is SDH used ?
SDH can be used in all of the traditional network application areas.
A single SDH network infrastructure is therefore possible which provides an efficient direct interconnection between the three major telecommunication networks.
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Notes on SDH rates
The most common SDH line rates in use today are 155.52 Mbps, 622.08 Mbps, 2.5 Gbps, 10 Gbps.
SDH is a structure that is designed for the future, ensuring that higher line rates can be added when required.
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SDH signal structure
The SDH signal is transported as a synchronous structure which comprises a set of 8-bit bytes organised into a two dimensional frame.
The ‘Truck analogy’ is a popular way to help us understand the contents of the SDH frame.
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SDH FRAME STRUCTURETRUCK ANALOGY
Tractor
Unit
Payload
Unit
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SDH FRAME STRUCTURETRUCK ANALOGY contd.
Virtual ContainerSection
Overhead
Payload
Payload OverHead
Multiplexer Section
OverHead
Regenerator Section
OverHead
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The Payload
The contents of the container carried by the truck represent the real value.
This ‘Payload’ is analogous to customer traffic, being carried by the ‘container’ within an SDH frame.
This Payload ‘container’ supports the transportation of spesific tributary signals.
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The Section Overhead
What actually gets the contentsof the truck to it’s destination is the tractor unit.
This analogous to the network maintenance and management capability carried by the SDH frame, known as it’s Section OverHead, or SOH.
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The Section Overhead (SOH) provides facilities that are required to support and maintain the transportation of customer traffic Safely across the network.
THE SOH is split into Multiplexer Section Overhead (MSOH) and Regenerator Section Overhead (RSOH).
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The Virtual Container
Even if the container is loaded on to a different truck, there is a portion of overhead that always remains with it.
This is known as the Path OverHead, or POH.
The Path Overhead is directly associated with the payload capacity area, and together they form what’s known as the Virtual Container.
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SDH FRAME STRUCTURE
STM-N FRAME STRUCTURE
270 x N Columns
261 x N Columns
9 x N Columns
9 R
ow
s = 8 bits/byte
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SDH FRAME STRUCTUREsignal frame transmission
The principle for SDH signal frame transmission is: the bytes (8-bit) within the frame structure is transmitted byte-by-byte (bit-by-bit) from left to right and from top to bottom. After one row is transmitted, the next row will follow. After one frame is completed, the next frame will start
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SDH FRAME STRUCTURESDH Rate
ITU-T defines the frequency to be 8000 frames per second for all levels in STM hierarchy
STM-1 Rate :
9 rows x 270 columns x 8 bits/byte x 8000 frames per second
= 155.52 Mb/s
STM-4 Rate :
9 rows x (270 x 4) columns x 8 bits/byte x 8000 frames per second
= 622 Mb/s
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OVERHEAD ANALYSIS
SDHTERMINAL
MULTIPLEXER
SDHTERMINAL
MULTIPLEXER
SDH
SDH DIGITALX-CONNECT
Multiplexer Section
Regenerator Section
Path
MSOH MSOHRSOHRSOH
RSOHPOH
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OVERHEAD ANALYSISPATH OVERHEAD
Path Trace message
Parity check
VC structure
Alarm & performance info
User channel
Multiframe indication for TUs
Path protection switching
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OVERHEAD ANALYSISPATH OVERHEAD contd.
• J1 : Path Trace byte
• B3: Path BIP8 Code
• C2: Signal label byte
• G1: Path status byte
• F2, F3: Path user channels bytes
• H4: TU position indicator byte
• K3: Spare byte
• N1: Network operator byte
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SDH Multiplexing Structure
STM-1 AU-4
TU-3
AUG-1
TUG-3 VC-3 C-3
VC-4 C-4
TU-12 VC-12 C-12
TUG-2
×1 ×1
×3
×1
×7
×3
139264 kbit/s
34368 kbit/s
2048 kbit/s
Pointer processing
Multiplexing
Mapping
Aligning
AUG-4
AUG-16
AUG-64
STM-4
STM-16
STM-64
×1
×1
×1
×4
×4
×4
Go to glossary
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SDH Tributary Multiplexing (34M)34 Mbit/s to STM-N
34M Rate Adaptation
Add POH
1
C3
1 84
9
125μs
1 1
9
VC3
POH
125μs1 85
Next page
Packing Mapping
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SDH Tributary Multiplexing (34M)
1st align
Fillgap
1 86
1
9
H1H2H3
R
×3
86
TU-3
1
H1H2H3
1
9
POH
R
R
VC-4
9
1
1 261
Aligning Stuffing
TUG-3
Multiplexing
3
Same as for C4
Multiplexing route: 1X34M 1XTU-3 3XTUG-3 1XAU-4---One STM-1 can load three 34Mbit/s signals
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SDH Tributary Multiplexing (2M)
2 Mbit/s to STM-N
2MNextpage
125μs
POH1 4
C12
1
9
VC12
1 4
1
9
TU12
1 4
1
9
TU-PTR
Rate Adaptation
Add POH
Packing
Add Pointer
Mapping Aligning
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SDH Tributary Multiplexing (2M)
×3
1 12
TUG-2
1
9
×7 R R
TUG-3
1 86
Multiplexing
1
9
MultiplexingSame as for C3
Multiplexing route: 1X2M 3XTU12 7XTUG-2 3XTUG-3 1XSTM-1--- One STM-1 can load 3X7X3 = 63X2M SignalsMultiplexing structure: 3-7-3 structure
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SDH Network protection SDH Network protection Bidirectional Traffic
Traffic flow direction along the ring
Clockwise or counter-clockwis
T1516670-94
The traffic shares the sameequipment and link
B
A
a) Uniformly routed
B
b) Diversely routed
The traffic is ondifferent equipment
and links
A
Unidirectional Traffic
Traffic flow direction along the ring
Clockwise and counter-clockwise
T1516670-94
The traffic shares the sameequipment and link
B
A
a) Uniformly routed
B
b) Diversely routed
The traffic is ondifferent equipment
and links
A
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Difference between Path and Multiplex SectionDifference between Path and Multiplex Section
Physical Layere.g. Optical fiber
Multiplex section
Path
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1+1 Linear MS Protection1+1 Linear MS Protection
Protection mechanism of 1+1linear MS protection system: Concurrent sending is permanent bridging Selective receiving is switching
selective receiving
concurrentsending
TU traffic TU traffic
concurrentsending
selective receivingswitch
switch
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1:N Linear MS Protection1:N Linear MS Protection
Structure of 1:N Linear MS ProtectionA B
Bridging Selector
Protection section (Transmit)
Working section 1(Transmit)
Protection section (Receive)
Working section 1(Receive)
Working section 2(Transmit)
Working section 2(Receive)
Working section N(Transmit)
Working section N(Receive)
Selector Bridging
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1:1 Linear MS Protection1:1 Linear MS Protection
Protection mechanism of 1:1 linear MS protection system: Traffic flow after protection switching
switch
switch
TU traffic TU traffic
Working
Protection
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Two-fiber uni-directional path protection ringTwo-fiber uni-directional path protection ring
Protection switching mechanism: Switching criteria
Transmission quality of each individual channel Usually TU-AIS, TU-LOP alarms
A
B
C
D
switch
S1
P1
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Traffic flow when network is broken: Working channels=1-N/2 AU4 Protection channesl=N/2-N AU4
Two-fiber bidirectional Multiplex Section Shared Protection RingTwo-fiber bidirectional Multiplex Section Shared Protection Ring
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APS controller: Transition of APS controller status:
Two-fiber bidirectional Multiplex Section Shared Protection RingTwo-fiber bidirectional Multiplex Section Shared Protection Ring
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Structure: Four fibers Working channels--S1,S2, carry normal traffic Protection channels--P1,P2, protect normal
traffic
Four-fiber bidirectional Multiplex Section Shared Protection RingFour-fiber bidirectional Multiplex Section Shared Protection Ring
CA AC
CA AC
S1P1
A
C
D B
P1S1
S2P2
P2S2
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SubNetwork Connection ProtectionSubNetwork Connection Protection Description:
Protection one SubNetwork Connection Can be adapted to all networks
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Normal condition for unidirectional SNCP: Concurrent sending (transmit end) Selective receiving (receive end)
SubNetwork Connection ProtectionSubNetwork Connection Protection
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Failure in working channels for unidirectional SNCP: Concurrent sending (transmit end) Selective receiving (receive end)
SubNetwork Connection ProtectionSubNetwork Connection Protection
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Protection Restoration: Restoration time - 10 minutes (5-12 minutes)
A
B
C
D
switch
S1
P1A
B
C
D
S1
P1
SubNetwork Connection ProtectionSubNetwork Connection Protection
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