SDH and TDM telecom

Synchronous Digital Hierarchy and Time Division Multiplexing

1. TDM and SDH Basics
TDM Time Division Multiplexing
SDH Synchronous Digital Hierarchy

2. Evolution.
A/D
8 kHz
64 kbit/s
BUT........

3. T1T2T3
T4T5T6T7
time Audio Signal
Sampler Output
time
T1T2T3
T4T5T6T7
Pulse Amplitude
Modulated (PAM)
signal
Sampling

4. +V0000X XXX
0001X XXX
0010X XXX
1000X XXX
1001X XXX
1010X XXX
1011X XXX
1100X XXX
1101X XXX
1110X XXX
1111X XXX
digital codes
-V
In accordance with
CCITT’s A-law
1/2V
1/4V
1/8V
1/16V
1/32V
1/64
V
Quantization
Level
32
48
64
80
96
112
Non-Linear Quantization and Encoding

5. 8
bits per
sample
x =
64kbit/s
8000
samples
per sec
PCM Signal Data Rate

6. Time Division Multiplexing (TDM)

7. 64 kbit/s
Data Signals
139264 kbit/s (+/-15ppm)
1
2048 kbit/s (+/-50ppm)
8448 kbit/s (+/-30ppm)
34 368 kbit/s (+/-20ppm)
64
Channel Capacity:
64 x 30 = 1920
DSMX
34/140
DSMX
8/34
DSMX
2/8
1
30
DSMX
64k/2
1
30
PCMX 30
1
PCMX 30
5
1
30
4
1
4
PDH Multiplex / Demultiplex
Analog signal

8. OLTU
34 - 140
8 - 34
2 - 8
OLTU
34 - 140
8 - 34
2 - 8
OLTU
34 - 140
8 - 34
2 - 8
OLTU
34 - 140
8 - 34
2 - 8
main
stand-by
140 Mbit/s 140 Mbit/s
Line Terminating
Unit
Line Terminating
Unit
Drop & Insert Station
1,2 ................. 64 1,2 ................. 64
Plesiochronous Drop & Insert

9. PDH vs. SDH — Bit Rates
E1
E0
E2
E3
E4
plesiochronous
plesiochronous
plesiochronous
synchronous
TM
STM-1
TM
STM-4
TM
STM-16
• E1 (2.048 Mbit/s)
• T1 (1.544 Mbit/s)
• DS-2 (6.312 Mbit/s)
• E3 (34.368 Mbit/s)
• DS-3 (44.736 Mbit/s)
• E4 (139.264 Mbit/s)
• ATM
• etc.
PDH
SDH

10. PDH vs. SDH — Add & Drop Function
ADM
STM-4STM-4
Six TMs needed
to drop E1
One ADM is
enough to drop E1.
TM TM
TMTM
TMTM
E 3
E 3
E 3
E 2
E 2
E 1
E 1
E 1
E 4 E 4
E 1 ( 2 . 0 4 8 k b i t / s )
E 2
2 / 1 2 / 1
3 / 23 / 2
4 / 3 4 / 3
PDH SDH

11. Simpler multiplexing
(low SDH level can be directly identified from higher SDH level)
Simple D&I of traffic channels
(direct access to lower level systems without synchronization)
Allows mixing of ANSI and ETSI PDH systems
SDH is open for new applications
(It can carry PDH, ATM, ETHERNET...)
SDH provides TMN (ECCs)
(for centralized network control)
Why SDH
Why SDH

12. Synchronous Network Structure
TM-1 ADM-1 TM-1
A CB
42 E1
A <=> C
21 E1
A <=> B
21 E1
A <=> B
21 E1
B <=> C
42 E1
A <=> C
21 E1
B <=> C
XC

13. 34Mbit/s
140Mbit/s
STM-1
STM-1 / STS-3c Gateway to SONET
DXC
ADMADM
ATM
Switch
STM-4/-162Mbit/s
34Mbit/s
STM-1
LAN
ADM
STM-1, STM-4
2Mbit/s
8Mbit/s
34Mbit/s
140Mbit/s
ADM : Add Drop Multiplexer
DXC : Digital Cross Connect
TM : Terminal Multiplexer
DSC: Digital Switching Center
LAN: Local Area Network
DWDM: Dense Wavelength Multiplexing
DSC
Synchronous Network Structure
DWDMDWDM

14. RSOH: Regenerator section overhead
MSOH: Multiplex section overhead
Payload: Area for information transport
Transport capacity of one Byte: 64 kbit/s
Frame capacity: 270 x 9 x 8 x 8000 = 155.520 Mbit/s
Frame repetition time: 125 µs
1
3
5
9
4
270
270 Columns (Bytes)
1 9
transmit
row by row
RSOH
MSOH
AU Pointer Payload
(transport capacity)
STM-1 Frame Structure
2430 bytes/frame × 8 bit/byte × 8000 frame/s = 155.52 Mbit/s
transmitted from top to bottom and left to right

15. 1
3
5
9
4
270
270 Columns (Bytes)
1 9
RSOHRSOH
MSOHMSOH
AU-4AU-4
AU PointerAU Pointer
VC-4VC-4
V
C
-
4

P
O
H
V
C
-
4

P
O
H
C-4C-4
STM-1 Frame Structure

16. Basic Elements of STM-1

17. J1
B3
C2
G1
F2
H4
F3
K3
N1
V5
J2
N2
K4
AU - PTR
VC-3/4 POH
VC-11/12/ 2 POH
STM-1 SOH
Media dependent bytes
X Reserved for national use
SOH: Section overhead
POH: Path overhead
The overheads (SOH, POH) are used for maintenance and
supervision of the SDH transmission network.
RSOH
MSOH
Payload
P


O


H
Pointer
A1 A1 A1 A2 A2 A2 J0 X X

D1 D2 D3
B2 B2 B2 K1 K2
D4 D5 D6
D7 D8 D9
D10 D11 D12
S1 M 1 E2 X X
B1 E1 F1 X X
H1 Y Y H2 1 1 H3 H3 H3
Embedded Overhead Bytes

18. Parity check
(B1 calculated by regenerator and multiplexers)
Data communication channels
(D1...D3, F1 between regenerators)
Voice communication channels
(E1 between regenerators)
Frame Alignment
(A1, A2)
Section Trace
(J0 Identfication
of regenerator source)
A1 A1 A1 A2 A2 A2 J0

B1 E1 F1
D1 D2 D3
B2 B2 B2 K1 K2
D4 D5 D6
D7 D8 D9
D10 D11 D12
S1 M1 E2
AU - Pointer
Functions of Regenerator Section Overhead

19. Parity check (B2)
Alarm information (K2)
Remote error indication (M1,K2)
 Automatic protection switching
(K1, K2 Bytes)
 Data communication channels
(D4 to D12 between multiplexers)
 Clock source information (S1)
 Voice communications channels
(E2 between multiplexers)
A1 A1 A1 A2 A2 A2 J0

B1 E1 F1
D1 D2 D3
B2 B2 B2 K1 K2
D4 D5 D6
D7 D8 D9
D10 D11 D12
S1 M1 E2
AU - Pointer
Functions of Multiplexer Section Overhead

20. A1, A2Frame synchronisation
B1, B2Parity bytes for transmission error monitoring
J0 Regenerator section trace
D1... D3Regenerator section DCC
D4.. D12Multiplex section DCC
E1, E2Orderwire for voice communication
F1 User channel for maintenance purposes (data, voice)
K1, K2Automatic protection switching (APS)
S1 Synchronisation status message
M1 MS-REI (remote error idication)
J1 Higher order path trace
B3 Path parity byte for error monitoring
C2 Signal Label (composition of payload)
G1 Path status and performance
F2, F3Path user channels
H4 Payload specific byte
K3 Automatic protection switching (APS)
N1 Network operator byte (Tandem Connection Monit.)
V5 Error check, path status, signal label
J2 Lower order path trace
N2 Network operator byte (Tandem Connection Monit.)
K4 Automatic protection switching (APS)
SOH
VC-3/4
POH
VC-1/2
POH
Overhead Byte Functionality

21. SDH Network Elements
TM
STM-N
or
PDH
STM-M
•Terminates RSOH and MSOH.
•May terminate HOP and LOP overhead.
•Multiplexes/maps tributary signals.
•Includes timing and management functions.
Terminal Multiplexer

22. SDH Network Elements
STM-N or PDH
STM-MSTM-M
ADM
•Terminates RSOH and MSOH.
•May terminate HOP and LOP overhead.
•Includes connection function between the two aggregates.
•Multiplexes/maps tributary signals.
•Includes a connection function for allocation of TUs within the STM frame.
•Includes timing and management functions.
Add/drop Multiplexer

23. SDH Network Elements
•Terminates RSOH and MSOH.
•Includes connection function between the aggregates.
•Can have tributary ports, for which it may terminate HOP and LOP
overhead.
•Includes timing and management functions.
STM-N or PDH
STM-MSTM-M DXC
Cross-connect

24. SDH Network Elements
Regenerator
•Regenerates the optical signal.
•Terminates RSOH.
REG
STM-N STM-N

25. Termination of Sections
Path
Multiplexing SectionsMultiplexing Sections
Regenerator Sections
TM TM