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The PDH hierarchy by JM Caballero

© Trend Communications

The telecommunication networks

POTS 1

2

3

2, 3 ,4

3

2

1

Information (1) only meaningful for the end user

Signals (2) modification of a physical characteristic: electricity, light, magnetism...relative to time

Transmission media (3) allow the movement of a signal from a source to a target

Nodes (4) relay the signals maintaining their characteristics. there are three basic types: regenerators, switches/routers and multiplexers

© Trend Communications

The PDH hierarchy

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Signals & Information

Information

Analog

Signals Digital

© Trend Communications

Analog

Digital

Modulation

Digital Modulation

- AM/FM radio

- ADSL

- broadcast TV

- digital TV

Digitalization

Codification

- audio CD

- ISDN (data)

- ISDN (voice)

- Internet

The PDH hierarchy

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Transmission media

Transmission types

Twisted pair

- Conductors Coaxial

Transmission obstruction

- Attenuation (loss of signal power) · proportional to the distance · the signal loses power · must have a good relation with noise

- Noise - Dielectrics

Optical Fiber

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

Space

- Distorsion (modification of the signal format) · different propagation speeds

© Trend Communications

The PDH hierarchy

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Telecommunication in evolution

© Trend Communications

The PDH hierarchy

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The arrival of digital technology analog Central

analog

Central

analog

: 1900 digital

digital

Modem

Modem

analog

digital

Central

Central

analog digital

digital

Central

Central

analog

digital

: 1960

: 1990

The telephone networks have moved to the digitalization. At the beginning on the local exchanges, backbones. The last step is the local loop.

© Trend Communications

The PDH hierarchy

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The digitalization of signals

SAM PLIN G

t t0

Q U AN TISATIO N

t0+T ··· 011 010 001 000 100 101 110 111

t

EN C O D IN G 001

011

001

101

100

t t0

t0+T ···

It is a process in order to transport analog information through a digital network © Trend Communications

The PDH hierarchy

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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.) 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/seg

64kbit/s is the basic rate, or the unit rate, in digital telecommunications

© Trend Communications

The PDH hierarchy

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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/s Bw: Bandwidth in Hz. P: Signal power N: Media noise

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

© Trend Communications

The PDH hierarchy

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Types of digital modulation 7V

3V

PA M

3V

t t0+T ···

t0

-V -3V

7V 5V 3V V -V -3 V -5 V -7 V

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

011 010 001 000 100 101 110 111

1

1

3

5

4

PD M

t t0+T ···

t0 t0+3T t0+4T t0

t0+T

t0+2T

t 1

1

3

5

4

PPM

t t0

t0+T ··· 001

011

001

101

100

PC M

t t0

t7 t0 t1 t2

t3 t4 t5 t6

t8 t9

A N A LO G PU LSE M O D U LA TIO N

t

D elta M odul.

t0+T ··· t4 t5 t6 t7

t0 t1 t2

t3

t8 t9

D IG ITA L PU LSE M O D U LA TIO N

t

Pulse Code Modulation (PCM) the most used for voice © Trend Communications

The PDH hierarchy

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Line Codifications Facts: •

An increase in data rate increases bit error rate



An increase in S/N decreases bit error rate



An increase in bandwidth allows increase in data rate

Evaluation factors: •

Avoid high frequency components for less bandwidth



Avoid DC component, just AC allows transformers & media isolation



Signal Synchronization embedded in the bit sequency avoids separate clock



Signal Error Detecting Capability provided by the nature of the codification



Signal Interference and Noise Immunity



Cost and Complexity

© Trend Communications

The PDH hierarchy

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Line Codifications (ii) 1 0 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 0

+V

NRZ

0

Non Return Zero

-V +V

AMI

2 Mbit/s 8 Mbit/s

0

Alternate Mark Inversion -V

HDB3 High Density Bipolar Three Zeroes

+V B

0

0

2 Mbit/s 34 Mbit/s

V

0 0

0

0

V

B

0

0

V

B: balancing V: violation

-V +V

CMI

Coded Mark Inverted

140 Mbit/s 155 Mbit/s

0 -V

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

© Trend Communications

The PDH hierarchy

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Multiplexing Allows the use of several communications channels through a transmission media

DTE-A

BWs1 BWC

BW

s2 DTE-B . . . BWs1 DTE-F

MULTIPLEXER Transmission media

FDMA

TDMA

Frequency Division Multiplexing Access

Time Division Multiplexing Access

CDMA Code Division Multiplexing Access 11 01 0 00 10 11 01110 0 1

A

F E

B C

D

B A F E D CB A

frequency

0 0 10 111 0111 0 1110 0 1

time

Radio, TV, GSM © Trend Communications

ISDN, Frame Relay,GSM

code

Bit

UMTS The PDH hierarchy

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Digital switching Analog switching & transmission: Inefficient, expensive •

Requires continuous modulation/demodulation



Noise is always present Modulator multiplexer

Demodulator demultiplexer A(f1)

A(f1) B(f2)

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

A(f1), B(f2)

Analog switch

C(f3) D(f4)

D(f4)

C(f3), D(f4)

4 channels at the same frequency

Digital switching & transmission •

Integrates in one operation the demultiplexing and switching



Easy to manage Digital switch ABABABABAB ABCDABCDABCDABCD CDCDCDCDCD

© Trend Communications

The PDH hierarchy

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Typical analog arrangement SU BSC R IBER S

PC M M U X 2 M bit/s

LTE R EG EN ER A TO R

A N A LO G EXC H A N G E

D IG ITAL TR A N SM ISSIO N LIN E

SU BSC R IBER S

R EG EN ER A TO R 2 M bit/s

LTE

The swictching capabilities are between subribers and digital multiplexors

© Trend Communications

The PDH hierarchy

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Typical digital arrangement SU BSCR IBERS

PCM M UX 2 M bit/s

LTE 2 M bit/s

2 M bit/s

REG EN ERA TO R

DIG ITAL EXCHANG E

DIG ITAL TRANSM ISSIO N LINE

REG EN ERA TO R

SU BSCR IBERS

PCM M UX

2 M bit/s

LTE 2 M bit/s

2 M bit/s

The swictching capabilities use to be inside and integrated with the digital network

© Trend Communications

The PDH hierarchy

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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

...but

© Trend Communications



Requires more Bandwidth



Needs synchronization

The PDH hierarchy

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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



Digital switching AT&T (USA 1962)



T-Carrier (USA 1965) CM 24 channels Western Electric



RSAN (Spain 1968) first public packet Network Telefonica



PDH (Europe 1975)



IDN (USA 70s) first full digital network



ISDN (Europe 1984) standarized voice and data metwork



SONET (USA 1988) first installations



B-ISDN (Europe 1990) SDH+ATM broadband networks



GSM (France 1994) digital wireless telephony



UMTS (Europe 2001) broadband wireless network

© Trend Communications

The PDH hierarchy

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Identify Digital Technology areas

Switching

Symplifies demultiplexing and switching operation Allows network management

Transmission

Allows TDMA to transmit several Allows error detection and quality measurements Mandatory for data cammunications

Signalling

Allows the development of advanced features when stablishing, maintaining or realease connections

Local loop

Allows advanced features for any applications based on voice, data, hypermedia or multimedia End-to-end digital quality

© Trend Communications

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The PDH standards IT U -T

T e le c o m m u n ic a tio n S ta n d a rd iz a tio n S e cto r o f th e In te rn a tio n a l T e le c o m m u n ic a tio n U n io n

R E C O M M E N D A T IO N S G S E R IE S :

T ra n s m is sio n s ys te m s a n d M u ltip le x a tio n e q u ip m e n t

O S E R IE S :

M e a s u rin g e q u ip m e n t s p e cific a tio n s

M S E R IE S :

T ra n s m is sio n s ys te m s m a in te n a n c e

Section

Multiplexing Hierarchies

Provides an standarized way for transmission and multiplexing in terms of rates and formats © Trend Communications

The PDH hierarchy

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PDH is the European hierarchy



It is digital



It is a hierachy because define four standarized layers for 2, 8, 34, and 140 Mbit/s



It is plesiochronous because each multiplexer can use its clock

© Trend Communications

The PDH hierarchy

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PDH is plesiochronous PDH PDH PDH PDH

PDH PDH

clock

PDH circuits alignment SWITCH

Lines Input

Synchronization

Switched lines

Plesio- means “almost” but truth is that each PDH island has its own clock: the result is an unsynchronized network

© Trend Communications

The PDH hierarchy

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PDH standard by ITU-T

hirarchy

standard

binary rate

line code

amplitude

attenuation

1

G.704/732

2048kbit/s±50ppm

HDB3

2.37V ó 3.00V

6dB

2

G.742

8448kbit/s±30ppm

HDB3

2.37V

6dB

3

G.751

34368kbit/s±20ppm

HDB3

1.00V

12dB

4

G.751

139264kbit/s±15ppm

CMI

1.00V

12dB

© Trend Communications

The PDH hierarchy

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PDH Frame stream sequence

© Trend Communications

The PDH hierarchy

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The PDH hierarchy

A

Remote Alarms Indicator (FAS and MFAS)

S

Spare bits (national use)

T1

i - Tributary bits

J11

Justification control bits

R1

Justification bits

ai bi ci di

i - Channel CAS bits

E

CRC-4 Error signaling bits

1

CAS multiframe alignment Frame alignment bits CRC-4 Multiframe alignment

© Trend Communications

0

Frame alignment supervision bits

C1 C2 C3 C4

Cyclic Redundancy Checksum bits

The PDH hierarchy

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Frame alignment

FA S

FA S

tim e slots



Allows targetting of synchronization to find the beginning of the frame



It needs the FAS word at the beginning of each odd framefor the 2 Mbit/s or at the beginning of the frame for the rest of the hierarchies

© Trend Communications

The PDH hierarchy

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The 2048Mbit/s basic frame



Multiframe composed by 16 frames, each one has 32 bytes



The first time slot is for the control, the 16 channel is for signalling



The frame period is 125 µs then 1byte is a 8 bit/125 µs= 64 kbit/s channel



The transmission rate is (32channel x 8bit/channel) / 125 µs = 2,048 Mbit/s

© Trend Communications

The PDH hierarchy

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The 2 Mbit/s basic frame (ii) B inary rate = 2048.0 Kbit/s ± 50 ppm Line C ode = H D B3 N om inalam plitude = 2.37 V (coaxialcable) 3.00 V (balanced cable) Im pedance = 75 (coaxialcable) Ω 120 (balanced cable) Ω Tolerated inputlevelattenuation = 0 to 6 dB at1024 Khz according to f √ Fram e length = 256 bits A vailable bits per tim eslot= 8 bits M ultiplexing m ethod = octetinterleaving Fram e rate = 8000 fram e/s FA S bits rate = 28000 bit/s (including supervision bit)= 32000 bit/s



It is the basic frame and the most used



All the european network equipment support



Most of the narrow band networks are built over this frame: POTS, Frame Relay, GSM, NISDN, and some leased lines, and ATM access networks

© Trend Communications

The PDH hierarchy

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The FAS for the alignment



FAS =0011011



FAS is only transmitted on odd frames the



NFAS uses a bit equal to “1” to avoid coincidences

© Trend Communications

The PDH hierarchy

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NFAS: Non Frame Alignment Sequence (i)

The second bit of the NFAS is equal to “1” and it is used to avoid aleatory coincidences with the FAS

© Trend Communications

The PDH hierarchy

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NFAS: Non Frame Alingment Sequence (ii)



The A bits are used for alarm management



The S bits are reserved space for opertators that want to implement management and maintenance protocols

© Trend Communications

The PDH hierarchy

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Check Redundancy Code CRC-4



It detects block errors. Each 4 bits CRC corresponds to the previous sub-multiframe



The receiver compute the submultiframe CRC and compares it with the code received on the next frame



If it does not match then an indition is sent using the E bit

© Trend Communications

The PDH hierarchy

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Error monitoring



This two bits indicate block errors detected by the CRC. First for the upper submultiframe and the second for the II submultiframe



“1” is the defect value



If multiplexer detects block errors then sets to “0” the bit E to the frame which is sent to the other side

© Trend Communications

The PDH hierarchy

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Multiframe alignment



The “001011” sequence is the alignment which is inserted on the odd frames



They must identify the CRC-4 submultiframe

© Trend Communications

The PDH hierarchy

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Distance alarm indication (bit A)

Used to send alarms to the remote side: •

Alarm bit used to indicate a power fault, loss of incoming signal, loss of frame, coder/ decoder fault, a very high bit error rate (>10-3) that do not allows recover the channels



Then the receiver sets the bit A=‘1’ on the frames travelling on the other direction



When transmitter realizes on the alarm state then send an AIS setting all the frame bits to ‘1’

© Trend Communications

The PDH hierarchy

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Spare bits



The bits S are reserved for the Network Operator internal use only



Usually are application, maintenance or monitoring of performance



If they are not used, or in international links, must be set to “1”

© Trend Communications

The PDH hierarchy

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The signalling channel

Used to interchange information between Local Exchanges (LE) •

Allows to establish, maintain an release end user connections.



Uses the time-slot TS16 of the 2 Mbit/s frame



Si is a four bits channel (a1, a2, a3, a4) i values goes from 1 to 30, one per channel

© Trend Communications

The PDH hierarchy

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Signalling channel methods



Channel Associated Signalling CAS Each 64 kbit/s channel (TS1-TS15 and TS17-TS30) has a 2 kbit/s channel, as fast as each one of the 30 signalling channel can be found at predefined positions



Common Channel Signalling (CCS) Byte oriented protocol. There is not a predefined position for each information channel because the protocol messages can be identified by means of an specific field

© Trend Communications

The PDH hierarchy

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Multiframe Alignment Signal (MFAS)



To synchronize the CAS an alignment signal



0000 sequence is found on the first bits of the multiframe

© Trend Communications

The PDH hierarchy

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No Multiframe Alignment Signal (NMFAS)

Used to send alarms to the remote side: •

Alarm bit used to indicate a power fault, loss of incoming signal, loss of multiframe CAS, coder/decoder fault, a very high bit error rate (>10-3) that do not allows recover the channels



Then the receiver sets the bit A=‘1’ on the frames travelling on the other direction



When transmitter realizes on the alarm state then sets all the bits of the CAS multiframe to indicate the alarm on the response from the remote side is to set CAS bits to ‘1’

© Trend Communications

The PDH hierarchy

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FAS - higher hierarchies FA S 140 M bit/s

111110100000 A S

T1 T2T3 T4

34 M bit/s tributaries bits

FA S 34 M bit/s

1111010000 AS T

1 T2 T 3T 4

8 M bit/s tributaries bits

FA S 8 M bit/s

1111010000 AS T

1 T2 T 3T 4

2 M bit/s tributaries bits

Uses some bits more depending on the bit rate

© Trend Communications

The PDH hierarchy

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Frame synchronization criteria

© Trend Communications

Bit rate

CCITT standard

Frame Alignment

Frame Loss

2048 Kbit/s

G.704/732

FAS, NFAS(bit 2), FAS

3 consecutive errored FAS

8448 Kbit/s

G.742

3 consecutive correct FAS

4 consecutive errored FAS

34368 Kbit/s

G.751

3 consecutive correct FAS

4 consecutive errored FAS

139264 Kbit/s

G.751

3 consecutive correct FAS

4 consecutive errored FAS

The PDH hierarchy

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8 Mbit/s channel structure 12 13

1

FAS

AST T T T

1 2 3 4

2121 T1T2T3 T4

212

45

Ji

T1 T2T3 T4T1

T4T1 T2T3 T4

1

Ji

45

212 1

45 T1 T2T3 T4 T1

T4 T1 T2T3 T4

Ji

212

89

Ri

T1 T2T3 T4 T1

T4T1 T2T3 T4

B in ary rate = 8448.0 K bit/s ± 30 ppm L in e C od e = H D B 3 N o m in al am p litu d e = 2.37 V Im p ed an ce = 75Ω T o lerated inp u t level atten u atio n = 0 to 6 dB at 4224 K hz according to f √ N u m b er o f trib u taries = 4 Ju stificatio n : P ositive bits Jij = 1 → R i = fill-in (justification) bits Jij = 0 → R i = inform ation (no justification) (decision is based on m ajority count of bits Jij)

M u ltip lexin g m eth od = bit interleaving F ram e rate = 9962.264 fram e/s F A S b its rate = 99622.64 bit/s M axim u m ju stificatio n rate p er trib u tary = 10000 bit/s approx. N o m in al ju stificatio n ratio = 0.424 F ram e len gth = 848 bits A vailab le b its p er trib utary p er fram e = 206 bits 848 bits F ram e d u ratio n = = 100.4 µ s 8448 kbit/s bits per tributary (per fram e) 206 bits T rib u tary R ate = = 100.4 µ s fram e duration

© Trend Communications

= 2051,7 kbit/s

The PDH hierarchy

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34 Mbit/s channel structure 12 13

1

FAS

AST T T T

1 2 3 4

384 1 T1 T2T3 T4

384

45

Ji

T1T2T3 T4 T1

T4 T1T2T3 T4

1

Ji

45

384 1

45 T1 T2T3 T4 T1

T4 T1 T2T3 T4

Ji

89

Ri

T1 T2T3T4 T1

384 T4T1 T2T3 T4

B inary rate = 34368.0 K bit/s ± 20 ppm Line C ode = H D B 3 N om inal am plitude = 1 V Im pedance = 75Ω Tolerated input levelattenuation = 0 to 12 dB at17.184 M hz according to √f N um ber of tributaries = 4 Justification :P ositive bits Jij = 1 → R i = fill-in (justification) bits Jij = 0 → R i = inform ation (no justification) (decision is based on m ajority countofbits Jij)

M ultiplexing m ethod = bitinterleaving Fram e rate = 22375.0 fram e/s FA S bits rate = 223750.0 bit/s M axim um justification rate per tributary = 22735 bit/s approx. N om inaljustification ratio = 0.436 Fram e length = 1536 bits A vailable bits per tributary per fram e = 378 bits 1536 bits Fram e duration = = 44.7 µs 34368 kbit/s bits per tributary (per fram e) 378 bits Tributary R ate = = fram e duration 44.7 µ s

© Trend Communications

= 8456,4 kbit/s

The PDH hierarchy

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140 Mbit/s channel structure 16 17

1

FAS 1

A S

T1 T2T3T4

T1 T2T3 T4T1

1

488

T1 T2T3 T4 T1

1

T4 T1 T2T3 T4

488

45

Ji

T1 T2T3 T4T1

1

T4 T1 T2T3 T4

Ji

T1 T2T3 T4 T1

Ji

T4 T1 T2T3 T4

89

45

1

(decision is based on m ajority countofbits Jij)

488

45

© Trend Communications

Binary rate = 139264.0 Kbit/s ± 15 ppm Line Code = CM I Vpp nom inal= 1 V Im pedance = 75 Ω Tolerated inputlevelattenuation = 0 to 12 dB at70 M hz according to f √ Num beroftributaries = 4 Justification :Positive bits Jij = 1 → R i= fill-in (justification) bits Jij = 0 → R i= inform ation (no justification)

T4 T1 T2T3 T4

45

Ji

T1 T2T3 T4

488

45

Ji

488

Ri

T1 T2T3 T4 T1

488 T4T1 T2T3 T4

M ultiplexing m ethod = bitinterleaving Fram e rate = 47562.842 fram e/s FAS bits rate = 570754.098 bit/s M axim um justification rate pertributary = 47563 bit/s approx. Nom inaljustification ratio = 0.419 Fram e length = 2928 bits Available bits pertributary perfram e = 723 bits 2928 bits Fram e duration = = 21.02 µs 139264 kbit/s bits pertributary (perfram e) 723 bits = 34394,2 kbit/s Tributary Rate = = 21.02 µs fram e duration

The PDH hierarchy

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Synchronization problems

8448 Kbit/s (+5 ppm)

8

8448 Kbit/s (+7 ppm) 34368 Kbit/s 8448 Kbit/s (+2 ppm) 8448 Kbit/s (-10 ppm)

34



The standard allows some offsets from the nominal bit rates because it is assumed the lack of synchronization on PDH networks



The problem appears when multiplexing to higher rate



In order to avoid errors the second, third and fourth hierachies provides mechanisms to accommodate the rate impairments

© Trend Communications

The PDH hierarchy

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Majority criteria for justification



If the tributary were absolutely synchronized with the multiplexed frame the it would use the R bit about the 50% of the opportunities



Then the multiplexer must set on all the Jik bits that belong to that tributary i.e.) if it is the second tributary would set J21, J22, J23 = 1 and R2=1



At the reception site a majority criteria is applied to identify if R bit contains information of the tributary or not. If it does the bits must be insert on the bit sequence when demultiplexing

© Trend Communications

The PDH hierarchy

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The justification mechanism



Bits Jik=1 then Ri is justification, no information



Bits Jik= 0 the Ri contains tributary information



if not all are 0s or 1s decision is based on majority count of Jik

Maximum justification rate. 2nd hierarchy: 9962,264 bits/s, 3rd hierarchy: 22375,0 bits/s, 4th. hierarchy: 47562,842 bits/s © Trend Communications

The PDH hierarchy

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Alarms - higher hierarchies

140, 34 y 8 Mbit/s

FAS

A S

T1T2T3 T4

The same functionality than 2 Mbit/s frame uses the full duplex capabilities of a link. It is used to indicate for alarms at higher rates: •

loss of signal



loss of frame (where the frame starts?)

© Trend Communications

The PDH hierarchy

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Spare channel - higher hierarchies

140 M bit/s.

34 M bit/s

8 M bit/s

FAS FAS FAS

A S S ST A ST

1

T2T3T4

A ST

1

T2T3T4

1T2T3

T4



general purpose bit that defines a channel which can be used by any operator application



some samples are maintenance or monitoring of performance

© Trend Communications

The PDH hierarchy

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PDH events hierarchy

ID

Explanation

All

AIS

Alarm Indication Signal

LOF

Loss Of Frame alarm

LOS

Loss Of Frame Signal alarm

RAI (RDI)

Remote Alarm Indication

FAS error

Alignment error

Bit error

Bit sequence mismatch (the patterns is known)

Code error

Violation on codification sequence

CRC-LOM

Cyclic Redundancy Checksum - Loss Of Multiframe

CAS-LOM

Channel Associated Signalling - Loss Of Multiframe

RLOM

Remote Loss Of Multiframe

CRC error

Redundancy Check error

REBE

Remote End Block Error

2Mbit/s

LOF RAI (bit A=1)

© Trend Communications

The PDH hierarchy

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Different AIS types

:X =1 2 Mbit/s AIS

TS16 AIS

8, 24, 140 Mbit/s AIS



AIS: all the tributary bits are “1”



Receiver detects it when tries to identify the FAS



TS16 AIS at the signaling channel. The rest of the bits are not modified

© Trend Communications

The PDH hierarchy

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The CRC-4 mechanism multiplexer

multiplexer

CRC4

errors.... 2 Mbit/s REBE (bit E=1)

1) CRC process 4) error indication reader

2) error detection 3) error indication writter



It is used for error detection as well as synchronization



It is OK for low error rates (< 10-6)



As all CRC It is not perfect the 6,25% of the errors are not detected



Each multiplexer informs to the partner the detected errors using the E bit:



Some of the old multiplexers does not implement this capabilities

© Trend Communications

The PDH hierarchy

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PDH as circuit provider POTS

POTS 8

Alquilada ISDN

8

2

2 8

Frame Relay

Internet

Alquiladas ISDN

8

2

2 8

8

8

8

GSM 2

34

Internet

34

2

GSM

ADSL

LMDS

Frame Relay

ADSL ATM

ATM

LMDS



PDH networks provide circuits to public and private networks like POTS, GSM, ISDN, FRL, audio, video, and data.



The 2 Mbit/s frame is used also to build the synchronization network.

© Trend Communications

The PDH hierarchy

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PDH some restrictions

© Trend Communications



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 high 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

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Test & Measurement

Section

How to measure

In Service Measurement

64

140

2 2 Mbit/s

2

140 Mbit/s

2 Mbit/s

(ISM) 2

2

140

64

FRAME ANALYZER

test equipment 64

140

2

2

140 Mbit/s

Out Of Service Measurement (OOS)

2

2

140 2 Mbit/s

64 2 Mbit/s

ERROR DETECTOR

PATTERN GENERATOR

test equipment

© Trend Communications

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Equalization Attenuation (dB) 140 Mbit/s

140 34 28

√f

8 2

EQUALIZATION f

Test equipment provides automatic equalization •

attenuation is bigger for high frequencies



amplification is a requirement

© Trend Communications

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Quality Measurements

%ROUTE ALLOCATION

OK

SERIAL OUTPUT

DEGRADED

LIMIT OK

BAD

LIMIT BAD

ITU-T Recommendations •

G.821 under 2Mbit/s,



G.826 applies to PDH and SDH,



M.2100 bringing into service and maintenance PDH



M2101.1 bringing into service and maintenance SDH

© Trend Communications

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