The PDH hierarchy - UGRelectronica.ugr.es/.../doc/Plesiochronous_Digital_Hierarchy.pdf · Plesiochronous Digital Hierarchy 2 / 32 The telecommunication networks Information only meaningful

© ICT electronics

The PDH hierarchy

© ICT electronics Plesiochronous Digital Hierarchy

2/32

The telecommunication networks

Informationonly meaningful for the end user

Signalsmodification of a physical characteristic: electricity, light, magnetism...relative to time

Transmission mediaallow the movement of a signal from a source to a target

Nodesrelay the signals maintaining their characterictics. There are three basic types: regenerator, switches/routers and multiplexers


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Signals & Information

Information

Analog Digital

signalsAnalog Modulation Digital Modulation

Digital Digitalization Codification


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Transmission media

- Conductors

- Dielectrics

Twisted pair

Coaxial

Optical Fiber

Space

- Attenuation

- Noise

- Distortion

· proportional to the distance· the signal loses power · must have a good relation with noise

· thermic· intermodulation (sum total of frequencies)· noise point

· different propagation speeds

Transmission types Transmission obstruction


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Telecommunication in evolution


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The arrival of digital technology

Modem

digitaldigital

digital

digitaldigital

analog

analog analog

analog

analog

digital

Modem

: 1900

: 1960

: 1990

LE LE

LE LE

LE LE


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t0 +T ···t0

t

t

0 1 10 1 00 0 10 0 01 0 01 0 11 1 01 1 1

t

0 0 1 0 1 1 0 0 1 1 0 1 1 0 0

t0 +T ···t0

SAMPLING

ENCODING

QUANTISATION

The digitalization of signals


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Nyquist Sampling theorem

“In order to convert an analog signal to digital it is necessary to use a sampling frequency (fs) at least two times the highest frequency”

• fs ≥ 2BW (in Hertzs)

i.e. to digitalize a phone channel BWc = 4000 Hz in 8 bits each sample it would be necessary:

• fs =2*4000=8000 Hz

T= 125µs: this is the base period for all digital networks

codifying:

• 8000 samples/seg* 8bits/sample = 64.000 bits/segthis is the basic speed for digital channels


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Capacity of a channel: the Shannon Law

The capacity of a noisy channel is :

• C= Bw log2 (1 + P/N)C: capacity of a channel in bit/sBw: Band width in Hz.P: Signal powerN: media noise

Show a max capacity for a noisy channel for transmitting digital information


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t

011010001000100101110111

t

001 011 001 101 100

t0+T ···t0

t

tt0+T ···t0

t

1 3 1 5 4

t0+T ···t0

tt0+T ···t0

tt0 t1 t2 t3 t4 t5 t6

t7 t8 t9

t0 t0+T t0+2Tt0+3T t0+4T

(3)(2)(1)(0)(4)(5)(6)(7)

7 V5 V

3 V V

- V-3 V

-5 V-7 V

3V 3V

- 3V

- V

7V

1 3 1 5 4

t0 t1 t2 t3

t4 t5 t6 t7

t8 t9

MODULATION

PAM

PDM

PPM

PCM

DeltaModul.

PULSEDIGITAL

MODULATIONPULSE

ANALOG

Types of digital modulation


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Line Codification

1 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 0

NRZ

AMI

HDB3

CMI

0

+V

-V

0

+V

-V

0

+V

-V

0

+V

-V

0 0 0 V

B 0 0 V

B 0 0 V

1 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 0


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Multiplexing

DTE-A BWs1

DTE-B BWs2

DTE-F

BWs1

.

.

.

MULTIPLEXER

Transmission channel

AA

BC

D

EF BCDEFAB

TDMAFDMA

BWC

f

t

frame

0 0 1 0 1 1 1 0 1 1 1 0 1 1 1 0 0 1

1 1 0 1 0 0 0 1 0 1 1 0 1 1 1 0 0 1

Bit Bit

CDMA


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Digital switching

A(f1), B(f2), C(f3), D(f4)

A(f1)

B(f2)

C(f3)

A(f1)

B(f2)

C(f3)

D(f4)D(f4)

A(f1), B(f2)

C(f3), D(f4)

Demodulatordemultiplexer

4 channels at thesame frequency

Analogswitch

Modulatormultiplexer

a) Analog switching

b) Digital switching

ABCDABCDABCDABCD

ABABABABAB

CDCDCDCDCD

Digital switch


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Advantages of digital technology

• Reduces hardware cost

• Simplifies swtiching

• Improves reliability, maintenance and quality

• Allows you to offer Quality of Service (QoS)

• Optimizes the use of resources

• Supports audio, data, video under a unified media

• Makes it easier to build computer networks

...but• Requires more Band Width

• Needs synchronization


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Digital milestones

• Telex (Germany 1935) first digital network

• Digitalization (France 1942)

• Fax (Japan 1950)

• Integration (USA 50´s) of transmission and switching

• AT&T (USA 1962) first PTT with digital switching

• Western Electric (USA 1965) first digital transmission PCM 24 channels

• Telefonica (Spain 1968) first packet network

• IDN (USA 70s) first full digital network

• ISDN (Europe 1984) standarized voice and data metwork

• SONET (USA 1988) first installations

• B-ISDN (1989) broadband networks

• ATM (1994) first public ATM net


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564992 Kbit/s

139264 Kbit/s

34368 Kbit/s

274176 Kbit/s

44736 Kbit/s

397200 Kbit/s

97728 Kbit/s

32064 Kbit/s

8448 Kbit/s

2048 Kbit/s

6312 Kbit/s

1544 Kbit/s

64 Kbit/s

x 30 x 24

x 4 x 3

x 4

x 4

x 4 x 4

x 3

x 7 x 5

x 6

x 4

x 3

5th level

4th level

3rd level

2nd level

1st level

single channel

Europe (CEPT) USA Japan

Plesiochronous Digital Hierarchies


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2

8

8 Mbit/s

2

8

8

34

COAXIAL CABLE

34

140

MUX

MUX

34 Mbit/s

2

8

2

8

8

34

140 Mbit/sMUX

LTE

TRANSMISSION MEDIA

SATELLITE

RADIO LINK

OPTICAL FIBRE

2 Mbit/s

PDH is a hierarchy

Four standarized mux levels 2, 8, 34 and 140 Mbit/s


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PDH is plesiochronous

SWITCH

clock

PDH

PDH

PDH

PDH

PDH

PDH PDH islands with their own clock

alignment


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The PDH hierarchy

A

S

T1

J11

R1

E

1

0

C1

ai bi ci di

Remote Alarms Indicator (FAS and MFAS)

Spare bits (national use)

i - Tributary bits

Justification control bits

Justification bits

i - Channel CAS bits

C2 C3 C4

CAS multiframe alignment

CRC-4 Multiframe alignment

Frame alignment bits

Frame alignment supervision bits

Cyclic Redundancy Checksum bits

CRC-4 Error signaling bits


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ch 16 ch 17 ch 30ch 1

SAMPLING RATE (of every channel): 8000 samples/s

CHANNEL BW: 0-3400 Hz

COMPRESSION LAW: AINVERSION OF EVENT BITS

BITS PER SAMPLE: 8 bits

Frame duration: 125 µs

ch 2 ch 15

CAS: 30 channels/frame

CCS: 31 channels/frame

Frame 0

Frame 1

Frame 15

ch 16 ch 18 ch 31ch 1 ch 2 ch 15 ch 17

SA SNFASFAS

NFAS

FASNFAS

s29

s1

s3

s14

s30s15

s16

s17

s18

MFASFAS

s2

The 2048Mbit/s basic frame


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Frame alignment

FAS FAS

tributaries bits

Allows targetting of synchronization to find the beginning of the frame


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FAS

FAS is only transmitted on odd frames NFAS uses a bit equal to “1” to avoid coincidences

TS17 TS18 TS31

S

TS16TS2 TS15

F A S

Frame Al ignment Superv ision bit

s16

s17

s18

s29

s30

s1

s2

s3

s14

s15

A S0000Frame 0

TS1

Frame 1

Frame 2

Frame 3

Frame 14

Frame 15

TS0

SA0 0 1 1 0 1 1C1

10

SA0 0 1 1 0 1 1C2

10

SA0 0 1 1 0 1 1C4

1E

Also called NFAS


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TS17 TS18 TS31

Frame 0

TS1 TS16

Frame 8

Frame 15

TS2 TS15TS0

C1 0 C2 0 C31 C4 0 C11 C21 C3 E C4 E

C1C2C3C4: CRC-4 check bits for the previous sub-multiframe

001011: CRC alignment signal

EE: CRC distant error indicating bits

Sub-Multiframe I

Sub-Multiframe II

SA SMFASFASNFASFAS

NFAS

FASNFAS

C1

C2

C1

0

0

EC4

FAS

s16

s17

s18

s29

s30

s1

s2

s3

s14

s15

s23s8

Cyclic Redundancy Checksum CRC-4

Allows the detection of errors


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NFAS: No FAS

Frame 0

TS1

Frame 1

Frame 2

Frame 3

Frame 14

Frame 15

TS2 TS31TS0

FASNFASFAS

NFAS

FASNFAS

Used to manage alarms and errors

8 Mbit/sDISTANT

8 Mbit/s

ALARM

FRAMELOSS

LTE LTE


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bit A: Remote Alarms Indication

TS17 TS31

SFrame 0

TS1 TS16

Frame 1

Frame 2

Frame 3

Frame 14

Frame 15

TS15TS0

s16

s17

s18

s29

s30

s1

s2

s3

s14

s15

A SSA

C1

10

SAC2

10

SAC4

1E

FAS

FAS

FAS

MFAS


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bits S for PTT use

TS17 TS31

SFrame 0

TS1 TS16

Frame 1

Frame 2

Frame 3

Frame 14

Frame 15

TS15TS0

s16

s17

s18

s29

s30

s1

s2

s3

s14

s15

ASA

C1

10

AC2

10

AC4

1E

FAS

FAS

FAS

MFASS SS S

SS SS S

SS SS S

SS

can be used for application, maintenance or monitoring of performance


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TS17 TS18 TS31

SFrame 0

TS1 TS16

Frame 1

Frame 2

Frame 3

Frame 14

Frame 15

TS2 TS15TS0

A Sb1a1 d1c1

b2a2 d2c2

b3a3 d3c3

b16a16 d16c16

b17a17 d17c17

b18a18 d18c18

MFAS

b29a29 d29c29

b30a30 d30c30

b14a14 d14c14

b15a15 d15c15

b29

d30c30b30

biai dici : i-channel signalling bits (CAS)

FASNFASFAS

NFAS

FASNFAS

0 0 0 0

MFAS for CAS

CAS Multiframe

Each of the 30 channels have associated 2 kbit/s, bits ai,bi,ci, di in TS16


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Multiframe Alignment Signal (MFAS)

S

TS16

A Sb1a1 d1c1

b2a2 d2c2

b3a3 d3c3

b16a16 d16c16

b17a17 d17c17

b18a18 d18c18

MFAS0 0 0 0

Used to synchronize the CAS

No MFAS(NMFAS)


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bit A in NMFAS (TS16)

TS17 TS31

SFrame 0

TS1 TS16

Frame 1

TS15TS0

s16s1

A SSA

C1

10FAS MFAS

Alarm bit used to indicate a power fault, loss of incoming signal, or loss of multiframe alignmentthen A=‘1’ the response from the remote side is to set CAS bits to ‘1’

A=1

CAS=1


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8 bit per sample8000 samples per second30 or 31 channels of information 125µs frame period 3.400 Hz bandwidth per channel

2 Mbit/s channel structure

Frame 0

Frame 1

Frame 15

ch 16 ch 18 ch 31ch 1 ch 2 ch 15 ch 17

SA SNFASFASNFAS

FASNFAS

s29

s1

s3

s14

s30s15

s16

s17

s18

MFASFAS

s2


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PDH as circuit provider

RTB

ATM

ISDN

Rented

Internet

2

8

2

8

2

8

2

8

2

8

2

8

34

8

GSM34

8

RTB

ATM

ISDN

Rented

Internet

GSM

PDH networks provide circuits to switched public networks.They are also used to build synchronization networks

FrameRelay Frame

Relay


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PDH network, some problems

• The supervision and maintenance functions are limited (just a few bits for alarms in NFAS, NMFAS and E bit (2 Mbit/s frame)

• In order to get low speed channel (i.e. 2 Mbit/s) from a hight hierarchy (i.e. 140 Mbit/s) a full demultiplexing is need

• Loss of compatibility between European, Japanese and North American hierachies

• There are no standards for speeds over 140 Mbit/s

• Low management capabilities

Documents

The PDH hierarchy - UGRelectronica.ugr.es/.../doc/Plesiochronous_Digital_Hierarchy.pdf · Plesiochronous Digital Hierarchy 2 / 32 The telecommunication networks Information only meaningful