TDM and SDH Basics

TDM Time Division Multiplexing

SDH Synchronous Digital Hierarchy

Evolution.

A/D

8 kHz

64 kbit/s

BUT........

T1 T2 T3

T4 T5 T6 T7time Audio Signal

Sampler Output

timeT1 T2 T3

T4 T5 T6 T7

Pulse Amplitude Modulated (PAM)

signal

Sampling

+V0 0 0 0 X XXX0 0 0 1 X XXX0 0 1 0 X XXX

1 0 0 0 X XXX1 0 0 1 X XXX

1 0 1 0 X XXX1 0 1 1 X XXX1 1 0 0 X XXX1 1 0 1 X XXX1 1 1 0 X XXX1 1 1 1 X XXX

digital codes

-VIn accordance with

CCITT’s A-law

1/2V1/4V

1/8V1/16V

1/32V

1/64V

Quantization Level

3248648096112

Non-Linear Quantization and Encoding

8bits per sample

x = 64kbit/s8000

samples per sec

PCM Signal Data Rate

Time Division Multiplexing (TDM)

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

DSMX34/140

DSMX8/34

DSMX2/8

1

30

DSMX64k/2

1

30

PCMX 30

1

PCMX 30

5

1

30

4

1

4

PDH Multiplex / Demultiplex

Analog signal

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

PDH vs. SDH — Bit Rates

E1E0

E2

E3E4

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

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

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

Synchronous Network Structure

TM-1 ADM-1 TM-1

A CB

42 E1

A <=> C

21 E1

A <=> B21 E1

A <=> B

21 E1

B <=> C

42 E1

A <=> C21 E1

B <=> C

XC

34Mbit/s 140Mbit/s STM-1

STM-1 / STS-3c Gateway to SONET

DXC

ADMADM ATMSwitch

STM-4/-162Mbit/s

34Mbit/sSTM-1

LAN

ADM

STM-1, STM-4

2Mbit/s

8Mbit/s34Mbit/s

140Mbit/s

ADM : Add Drop MultiplexerDXC : Digital Cross ConnectTM : Terminal MultiplexerDSC: Digital Switching CenterLAN: Local Area NetworkDWDM: Dense Wavelength Multiplexing

DSC

Synchronous Network Structure

DWDMDWDM

RSOH: Regenerator section overheadMSOH: Multiplex section overheadPayload: Area for information transport

Transport capacity of one Byte: 64 kbit/sFrame capacity: 270 x 9 x 8 x 8000 = 155.520 Mbit/sFrame repetition time: 125 µs

1

3

5

9

4

270

270 Columns (Bytes)

1 9transmitrow 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

1

3

5

9

4

270

270 Columns (Bytes)

1 9

RSOHRSOH

MSOHMSOH

AU-4AU-4

AU PointerAU PointerVC-4VC-4

VC

-4 P

OH

VC

-4 P

OH

C-4C-4

STM-1 Frame Structure

Basic Elements of STM-1

J1B3C2G1F2H4F3K3N1

V5J2N2K4

AU - PTR

VC-3/4 POH

VC-11/12/ 2 POH

STM-1 SOH

Media dependent bytesX Reserved for national use

SOH: Section overheadPOH: 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 K2D4 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

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

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

A1, A2 Frame synchronisationB1, B2 Parity bytes for transmission error monitoringJ0 Regenerator section trace D1... D3 Regenerator section DCCD4.. D12 Multiplex section DCCE1, E2 Orderwire for voice communicationF1 User channel for maintenance purposes (data, voice)K1, K2 Automatic protection switching (APS)S1 Synchronisation status messageM1 MS-REI (remote error idication)

J1 Higher order path traceB3 Path parity byte for error monitoringC2 Signal Label (composition of payload)G1 Path status and performanceF2, F3 Path user channelsH4 Payload specific byteK3 Automatic protection switching (APS)N1 Network operator byte (Tandem Connection Monit.)

V5 Error check, path status, signal labelJ2 Lower order path traceN2 Network operator byte (Tandem Connection Monit.)K4 Automatic protection switching (APS)

SOH

VC-3/4POH

VC-1/2POH

Overhead Byte Functionality

SDH Network Elements

TMSTM-N

orPDH

STM-M

• Terminates RSOH and MSOH.

• May terminate HOP and LOP overhead.

• Multiplexes/maps tributary signals.

• Includes timing and management functions.

Terminal Multiplexer

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

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

SDH Network Elements

Regenerator

• Regenerates the optical signal.

• Terminates RSOH.

REG

STM-N STM-N

Termination of Sections

Path

Multiplexing Sections Multiplexing Sections

Regenerator Sections

TM TM