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© Tejas Networks India Ltd., 2004, Confidential Information
Synchronous Digital Hierarchy
SDH

Objective
Early transmission systems
Types of transmission
SDH
• Frame Structure
• Equipments
• Topologies
• Advantages

Telecommunication – what is it?
Telecommunications :
Electronic Communication at a distance
Take an Example of Telephone Transmission:
Information
Electrical Signal
Information
Transmission Medium
Transmitter Receiver

300 Hz to
10 Khz
300Hz to
3.4 KHz
One Voice channel
4 Khz Bandwidth
Voice signal - Band limited to 3.4 Khz
3.4 Khz signal – ‘intelligible component’
of human voice
Voice signal converted into its equivalent
electrical form and then transmitted
Base band transmission – Transmission
of information signal in its electrical form
Base band transmission - Severe
distance limitations due to low power
Base band transmission – Transmission
line can carry only one signal, wasting
available high capacity
Base band Transmission

Broad band communication – Transmission of information signal after
Modulation
Modulation - Carrying the information signal using a high frequency ‘Carrier’
Broad band - Signals travel long distances due to their higher power
Broad band signals allow for ‘Multiplexing’, a technique used to carry many
channels on a single transmission line
Multiplexing – Carrying multiple communication signals simultaneously on a
single transmission line
Modulation and Multiplexing – Each information signal modulated onto multiple
carriers of different frequencies
Multiplexed system – Enables complete utilisation of bandwidth available on a
transmission line
Broadband Transmission

Electrical signal carrying information
in the form of continuous wave
transmitted over a transmission line
Easily affected by Noise
Analog Transmission

Information signal Digitised before transmission
Digitised signal is a periodic binary pulse
Digital signals have better noise immunity
Digital Transmission

Digitisation Process
4 Khz Voice signal is sampled at twice the
frequency ie., 8000 Hz
Samples are Quantised- Benchmarked to nearest
predefined levels
Quantised samples are encoded using 8 binary
bits
Each Voice channel hence occupies
8x8000 = 64000 bits per second = 64 Kbps
00000001
00000010
00000011
.
.
.
.

Digital Transmission Types - Asynchronous Communication
Internal Clock 1 Internal Clock 2
N/W 1 N/W 2
Transition of signals do not
occur at the same nominal rate
Generally free running quartz
oscillators derive the clock, no
timing pulses sent from
transmitter to receiver

Digital Transmission Types – Plesiochronous Transmission
Transitions occur at almost same rate
with variations within tight limits
Stable primary
reference clock
N/W 1
N/W 2
N/W 3
Slave to primary
reference clock

PDH - Standards
139264 KbpsE4
34368 KbpsE3
8448 KbpsE2
2048 KbpsE1
64 KbpsE0
Data RateNotation
139264 KbpsT4/DS4
44736 KbpsT3/DS3
6312 KbpsT2/DS2
1544 KbpsT1/DS1
64 KbpsT0/DS0
Data RateNotation
European Standard
American Standard
Used in South America, Europe,
India etc
Used in South America, Europe,
India etc
Used in USA, Canada, Japan,
Korea, Hong Kong etc

PDH - Limitations
The maximum standard defined is upto 140Mbps and cannot serve higher
standards
PDH supports mostly point to point systems
The different standards defined for North America and Europe are not
interoperable

Stable primary
reference clock
N/W 1
N/W 2
N/W 3
Slave to primary
reference clock
Digital Transmission Types – Synchronous Transmission
All Transitions occur at the same time
Entire network has single primary
reference clock

The hierarchy is as follows:
39813.12 Mbps
9953.280 Mbps
2488.320 Mbps
622.080 Mbps
155.52 Mbps
51.84 Mbps
Bit Rate
40 GbpsSTM-256
10 GbpsSTM-64
2.4 GbpsSTM-16
622 MbpsSTM- 4
155 MbpsSTM-1
51 MbpsSTM-0
Abbreviated asElectrical Signal
SDH - Standards

9 Rows
Administrative Unit
Capacity of the
Virtual Container
+
Pointers
1
2
3
4
5
6
7
8
9
Regenerator
Section
Overhead
Multiplex
Section
Overhead
H3H1 H2Pointers
STM-1 = 270 Columns (2430 bytes)
H1H1 H1 H2 H2 H2 H3 H3 H3
Frame = 125 sµ Frame = 125 sµFrame = 125 sµ
Overhead width = 9 columns
SDH – Frame Structure

SDH Frame StructureSDH Frame Structure –– Overhead AnalysisOverhead Analysis
Path
Termination
Equipment
Section
Termination
Multiplex Section
Termination
Path
Termination
Equipment
Section
Termination
Path
Multiplex Section
Regenerator Section Regenerator Section
Multiplex Section
PTE Reg ADM Reg PTE

STM Frame Format
STM-1 frame is divided into two broad units
Section overhead and Administrative unit
Section overhead – this information is further
classified as Regenerator section overhead
and Multiplex section overhead
Payload along with Path overhead
information forms the Virtual container
Pointer – Indicates the start of the
Virtual container
Payload contains data in the form of tributary frames
E1, T1, E3, Ethernet etc
Payload
STM-1
155 Mbps
Administrative
unit
Pointer
Virtual
Container
Path
overhead
Section
Overhead
Regenerator
Overhead
Multiplex
overhead

D3D2D1
F1E1B1
A1A1 A1 A2 A2 A2 J0
SDH Frame StructureSDH Frame Structure –– RSOHRSOH
Frame Alignment - A1,A2
Parity Check - B1
Regeneration Section Trace - J0
Orderwire channels for voice comm- E1
User Channel - F1
Data Communication Channel - D1-D3
Regenerator
Section

E2M1S1
D12D11D10
D9D8D7
D6D5D4
K2K1B2B2B2
Parity Check- B2
Automatic Protection Switching- K1,K2
Data Communication Channel- D4-D12
Synchronous Status Message – S1
Remote Error Indication- M1
Orderwire (voice comm)- E2
SDH Frame StructureSDH Frame Structure –– MSOHMSOH
Multiplex
Section

N1
K3
F3
H4
F2
G1
C2
B3
J1
Path trace – J1
Parity Check – B3
Path signal label –C2
Path status –G1
Path user channel – F2,F3
Position indicator – H4
Automatic Protection
switching - K3
Network operator – N1
SDH Frame StructureSDH Frame Structure –– POH functionsPOH functions
Path
Overhead

SDH Multiplexing
C-11
C-12
C-2
C-3
C-4
VC-11
VC-12
VC-2
VC-3
TU-11
TU-12
TU-2
TU-3
TUG-2
TUG-3
VC-3
VC-4
AU-3
AU-4AUGSTM-N
1544kbps
2048kbps
6312kbps
44736kbps
34368kbps
139264kbps
x4
x3
x1
x1
x3
x7
x3
x1xN
x7

SDH Equipment
Terminal Multiplexer
• Path Termination equipment which acts as
concentrator of tributary signals like E1
Regenerator
• Regenerator is used to boost the signals
between multiplexers placed across a long
distance
Path Termination
Equipment
Path Termination
Equipment
Regenerator
STM-N E 1
E 3
T 1

SDH - Equipments
Add-Drop Multiplexer
•Add Drop Multiplexer is used to access the signals
to be dropped or inserted while allowing the other
signals to pass through without processing
Cross Connect System
• Cross Connect system performs the time slot
interchange and grooming function of STM-N signal
STM-NSTM-N
Left Right
E 3T 1 E 1
STM-N

SDH- Network Topologies
Point to Point
• Involves two terminal multiplexers
connected together with an optical
fiber with or without regenerators
Point to Multipoint
• This configuration necessarily
involves a Add Drop Multiplexer
which connects to multiple sites
adding or dropping signals at
each site
PTE Regenerator PTE
PTE
Regenerator
ADM PTE
Regenerator

MUX
Regenerator
DCS
Regenerator
Regenerator
MUXMUX
MUX
Regenerator
Hub Configuration
• Hub configuration involves a Digital Cross
Connect System at the centre of a mesh network,
grooming the traffic from various directions.

ADM
ADM ADM
ADM
Ring Configuration
• Ring configuration involves multiple ADMs
connected along the optical fiber ring either in
bi-directional or Uni-Directional connectivity

SDH Advantages
Availability of high speed standards required for Optical Network which can carry
huge capacity
Efficient Multiplexing/Demultiplexing
Enhanced Operation, administration, Provisioning, Maintenance capabilities
SDH enables ready interconnection of multi vendor equipment

Thank You…Thank You…Thank You…Thank You…

Sdh

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