The document provides an introduction to PDH and SDH technologies, describing the frame structures and multiplexing hierarchies of PDH and how SDH was developed as an international standard to address limitations of PDH such as lack of world standards for digital formats and optical interfaces. Key aspects of SDH are explained including the STM frame structure, multiplexing structure, path layers, pointer processing, and overhead bytes.

1. July 2014, v1
Introduction to PDH & SDH technology

2. Proprietary and Confidential
Agenda
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• Plesiochronous Digital Hierarchy PDH
• E1 frame structure
• PDH Hierarchy
• PDH Limitation
• STM-1 frame structure
• SDH Multiplexing Structure
• KLM Numbering Scheme
• VC-12 Mapping Structure
• RSOH byte Description
• MSOH byte Description

3. Proprietary and Confidential
• PDH is a technology used in telecommunications networks to transport large quantities of data over
digital transport equipment.
• The term plesio-chronous refers to the fact that PDH networks run in a state where different parts of the
network are nearly, but not quite perfectly, synchronized.
• Difference in clock between PDH elements is compensated by signalling between the Tx and Rx to
indicate missing bits.
• The transmitting multiplexer adds additional bits to allow the far end receiving multiplexer to decode
which bits belong to which 2-Meg data stream. These additional bits are called "justification" or "stuffing"
bits.
• The basic unit in PDH is called the E0 and has a rate of 64Kbps.
• There are two different PDH systems, European and American systems.
Notation Data Rate
E0 64 Kbps
E1 2048 Kbps
E2 8448 Kbps
E3 34368 Kbps
E4 139264 Kbps
Notation Data Rate
T0/DS0 64 Kbps
T1/DS1 1544 Kbps
T2/DS2 6312 Kbps
T3/DS3 44736 Kbps
T4/DS4 139264 Kbps
European Standard
(30 E0 + 2 E0 for signalling)
American Standard
(24 E0 + framing bits)
PDH (Plesiochronous Digital Hierarchy)
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4. Proprietary and Confidential
E1 frame structure:
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• An E1 link operates over two separate sets of wires, usually Unshielded twisted pair (balanced cable) or using coaxial (unbalanced
cable). A nominal 3 volt peak signal is encoded with pulses using a method avoiding long periods without polarity changes. The
line data rate is 2.048 Mbit/s (full duplex, i.e. 2.048 Mbit/s downstream and 2.048 Mbit/s upstream) which is split into 32 timeslots,
each being allocated 8 bits in turn. Thus each timeslot sends and receives an 8-bit PCM sample, usually encoded according to A-
law algorithm, 8000 times per second (8 × 8000 × 32 = 2,048,000). This is ideal for voice telephone calls where the voice
is sampled at that data rate and reconstructed at the other end. The timeslots are numbered from 0 to 31.
• The E1 frame defines a cyclical set of 32 time slots of 8 bits. The time slot 0 is devoted to transmission management and time slot
16 for signaling; the rest were assigned originally for voice/data transport.
TS0 – reserved for framing purposes
TS16 – reserved for signaling

5. Proprietary and Confidential
PDH hierarchy
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6. Proprietary and Confidential
• No world standard on digital format. Making equipment to convert
different standards is costly.
• No world standard for optical interfaces. Networking is impossible at
the optical level.
• Rigid asynchronous multiplexing structure. No direct multiplexing.
• Limited management capability.
PDH Limitations
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7. Proprietary and Confidential
• International Telecommunication Union – ITU standard
• First set of SDH recommendations released in 1988
• A flexible and efficient method to convey digital information from
one designated location to another
• An international standard for high-speed optical and electrical
telecommunications networks
• Solution for data-transmission in broadband
telecommunications network
SDH (Synchronous Digital Hierarchy)
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8. Proprietary and Confidential
• Direct mapping (transport) of PDH (TDM), ATM and IP signals
• Effective and powerful multiplexing, de-multiplexing and cross connecting
• Standardised NNI for both optical and electrical interfaces
• Dynamic network protection in ring topology (self healing)
• In service supervision and management for all Network Elements (NE)
• Centralised network control and timing recourses
Advantages of SDH
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9. Proprietary and Confidential
Network elements
DXC - Digital Cross Connect
ADM - Add/Drop Multiplexer
TM - Terminal Multiplexer
RT - Radio Terminal
RR - Radio Repeater
OR - Optical Repeater
Typical Capacity
Access network: PDH, STM-0, STM-1
Regional network: STM-1, STM-4, STM-16
National network: STM-16, STM-64
ADM
ADM
ADM
Regional
network
(Ring)
Access network
(Chain)
RT RT
RR
RT
RT
National network
(Mesh)
DXC
DXC
RT
DXC OR RT
OR
DXC OR
TM
Components and topology
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10. Proprietary and Confidential
• Frame header + Payload = Synchronous Transport Module (STM)
The SDH frame
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11. Proprietary and Confidential
MSOH
AU - pointers
STM -1 payload
RSOH
261 bytes
270 bytes
9 bytes
3 rows
5 rows
1 row
STM - 1 bit rate:
8000 frames/sec x 9 rows/frame x 270 bytes/row x 8 bits/byte = 155.520 Mb/s
STM-1 Frame Structure
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12. Proprietary and Confidential
MSOH
AU - pointers
STM -n payload
RSOH
nx261 bytes
nx270 bytes
nx9 bytes
3 rows
5 rows
1 row
STM - n bit rate:
nx8000 frames/sec x 9 rows/frame x 270 bytes/row x 8 bits/byte = nx155.520 Mb/s
STM-n Frame Structure
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Signal name Bit Rate AKA
STM-0 51.84 Mbps 51 Mbps
STM-1 155.52 Mbps 155 Mbps
STM- 4 622.080 Mbps 622 Mbps
STM-16 2488.320 Mbps 2.4 Gbps
STM-64 9953.280 Mbps 10 Gbps
STM-256 39813.12 Mbps 40 Gbps

13. Proprietary and Confidential
Section Layers
MST - Multiplexer Section Termination (DXC, ADM, TM)
RST - Regenerator Section Termination (RT, RR, OR)
MS - Multiplexer Section
RS - Regenerator Section
RST
MST
MST
MST
RST RST RST
RST
RS RS
RS RS
MS
RS
RS
RS
MS
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14. Proprietary and Confidential
RST
MST
MST
MST
RST RST RST
RST
RS RS
RS RS
MS
RS
RS
RS
MS
Path layer
Higher order path
VC-3 (34 Mb/s)
VC-4 (140 Mb/s)
Mapped ATM / IP
Path Layers
Lower order path
VC-12 (2Mb/s)
Mapped ATM / IP
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15. Proprietary and Confidential
SDH Multiplexing Structure
Pointer
Processing
Multiplexing
Mapping
C-nx : Container
VC.nx : Virtual Container
TU-nx :Tributary Unit
AU-n : Administrative Unit
TUG-n : Tributary Unit Group
STM-N : Synchronous Transport Module
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16. Proprietary and Confidential
K L M Numbering Scheme, TU-12 Structure
MSOH
RSOH
AU-P
K = 1 K = 3
K = 2
L = 1
L = 2
L = 3
L = 4
L = 5
L = 6
L = 7
M=1 M=2 M=3
VC-12 # 34
( K=2,L=5,M=1)
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17. Proprietary and Confidential
VC-12 Mapping Structure
C-12
Container for 2.048 Mb/s C - 12
C-12
VC - 12 POH VC - 12
POH C-12
TU - pointer TU - 12
TU - 12
TU - 12
TU - 12
Byte interleave 3 x TU - 12 TUG - 2
Byte interleave 7 x TUG - 2
TUG - 3
Byte interleave 3 x TUG - 3
TU - 12
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C-4
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18. Proprietary and Confidential
VC - 4 POH VC - 4
RSOH
STM - 1
TU - 12
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POH
AU - Pointer
AU - 4
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POH
AU-Pointer
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J0
A 2
A
A
A1
A1
A1 A2 A2 A
B1 E1 F1 N N
D1 D2 D3
H2 H2 H2 H3 H3 H3
H1
B2 B2 B2 K1 K2
D4 D5 D6
D7
D10
S1 Z 1 Z1 Z 2 Z2 M1 E2 N
D9
D1 2
D8
D 11
N
H1
A1
A1
H1
A 1
MS 2
SI
#1 #2 #3
N
MS 3
MS 1
N
VC-4
POH
MSOH
VC-12 Mapping Structure
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19. Proprietary and Confidential
J0
A2
A
A
A1
A1
A1 A2 A2 A
B1 E1 F1 N N
D1 D2 D3
H2 H2 H2 H3 H3 H3
H1
B2 B2 B2 K1 K2
D4 D5 D6
D7
D10
S1 Z1 Z1 Z2 Z2 M1 E2 N
D9
D12
D8
D11
N
STM-1
RSOH
POINTER
STM-1
MSOH
H1
A1
A1
H1
A1
MS
2Mb/s
Media Specific
bytes
2 Mb/s asynchronous
.
MS 2
SI
#1 #2 #3
N
MS 3
MS 1
SI : Stuffing for 2Mb/s Wayside
MS 1&2 : Radio Protection Switching
control
MS 3 : RF-Id
Remote reset
ATPC
E/M for bytes; E1, F1, E2
N
SOH - Section Overhead
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20. Proprietary and Confidential
A1/A2 - STM -1 frameword. (A1: 11110110, A2: 00101000)
J0 - Regenerator section trace
B1 - Regenerator section error calculation (BIP-8)
E1 - Regenerator Orderwire
F1 - Regenerator User channel
D1/D2/D3 - Data Communication Regenerators (192Kb/s)
NU - National Use
MS - Media Specific bytes
UN - UNallocated bytes
A1 A1 A1 A2 A2 A2 J0 NU NU
B1 MS MS E1 UN UN F1 NU NU
D1 MS UN D2 UN UN D3 UN UN
RSOH - Byte Description
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21. Proprietary and Confidential
B2 - Multiplexer section error calculation (BIP-24)
K1/K2 - Multiplexer protection switching
D4-D12 - Data Communication Channel multiplexer (576Kb/s)
Z1/Z2 - Reserved for future use
E2 - Multiplexer Orderwire
S1 - Syncronization status
M1 - Multiplex Section - Remote Error Identifier (MS-REI)
NU - National Use
UN - UNallocated bytes
B2 B2 B2 K1 UN UN K2 UN UN
D4 UN UN D5 UN UN D6 UN UN
D7 UN UN D8 UN UN D9 UN UN
D10 UN UN D11 UN UN D12 UN UN
S1 Z1 Z1 Z2 Z2 M1 E2 NU NU
MSOH - Byte Description
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22. Thank you
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