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- Words: 4,571
- Pages: 60
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
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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
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Telecommunication in evolution
© Trend Communications
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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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60
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
The PDH hierarchy
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60
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
The PDH hierarchy
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60
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
The PDH hierarchy
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60
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
The PDH hierarchy
60/
60
© 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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60
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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60
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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60
Telecommunication in evolution
© Trend Communications
The PDH hierarchy
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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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
15/
60
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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60
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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60
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
The PDH hierarchy
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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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60
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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60
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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60
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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60
PDH Frame stream sequence
© Trend Communications
The PDH hierarchy
25/
60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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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60
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
The PDH hierarchy
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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
The PDH hierarchy
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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
The PDH hierarchy
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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
The PDH hierarchy
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