Pulse code modulation (PCM) is a method of digitally representing sampled analog signals. In PCM, the instantaneous voltage of an analog signal is sampled regularly at uniform intervals, then quantized to a series of digital codes. This allows the analog signals to be transmitted over digital communication networks or stored in digital memory. Key aspects of PCM include sampling the analog signal, quantizing the samples to discrete levels, encoding the quantized levels into binary code words, and transmitting the encoded binary data as a serial bit stream. PCM provides advantages like noise immunity, easy processing and storage, and the ability to multiplex and transmit multiple signals over the same channel.

1. PULSE CODE MODULATION
(PCM)
1

2. Frequency Division Multiplexing (FDM)
2

3. 3

4. PULSE CODE MODULATION (PCM)
( )
DEFINITION: Pulse code modulation (
l d d l (PCM) is essentially analog‐
) ll l
to‐digital conversion of a special type where the information
contained in the instantaneous samples of an analog signal is
represented by digital words in a serial bit stream
stream.
The advantages of PCM are:
• Relatively inexpensive digital circuitry may be used extensively.
• PCM signals derived from all types of analog sources may be merged with
data signals and transmitted over a common high‐speed digital
y
communication system.
• In long‐distance digital telephone systems requiring repeaters, a clean PCM
waveform can be regenerated at the output of each repeater, where the
input consists of a noisy PCM waveform.
• The noise performance of a digital system can be superior to that of an
analog system.
• The probability of error for the system output can be reduced even further
by the use of appropriate coding techniques.
SKGOCHHAYAT,SDE,RTTCBHUBANESWAR

5. 4.1 Digital Modulation
• Advantages :
– Immunity to noise
– Easy storage and processing: MP, DSP, RAM, ROM, Computer
– Regeneration
– Easy to measure
– Enables encryption
– Data from several sources can be integrated and transmitted using
the same digital communication system
– Error correction detection can be utilized
• Disadvantages :
– Requires a bigger bandwidth
– Analog signal need to be changed to digital first
– Not compatible to analog system Voice : Analog : 4 kHz
– Need synchronization Digital : 2 x 4 kHz x 8 bit = 64 kb/s
BWmin = 32 kHz
i
5

6. A brief aside about ADCs
• ADCs are used to convert an analogue input voltage into a number that can
be interpreted as a physical parameter by a computer.
computer
1111 Resolution=
1110 1 part in 2n
1100
1101
1011
1010
1001
1000
0111
0110
0100
0010
0101
0011
0001
1000 1110 1111 1011 0100 0001 0011
Numbers passed from ADC to computer to represent analogue voltage
6

7. Analog to Digital Conversion
The Analog‐to‐digital Converter (ADC)
performs three functions:
Analog – Sampling
Input • Makes the signal discrete in time.
Signal
Si l
• If the analog input has a bandwidth
Sample
of W Hz, then the minimum sample
frequency such that the signal can
be
b reconstructed without di t ti
t t d ith t distortion.
ADC – Quantization
Quantize • Makes the signal discrete in
111
110 amplitude.
l d
101
100
011
• Round off to one of q discrete levels.
010
Encode
001
000
– Encode
• Maps the quantized values to digital
words that are 8 bits long.
If the (Nyquist) Sampling Theorem is
Digital Output satisfied, then only quantization introduces
f d h l d
Signal distortion to the system.
111 111 001 010 011 111 011

8. Basic Steps For PCM System
• Filtering
• Sampling
• Quantization
Q i i
• Encoding
• Line Coding
• FILTERING Filters are used to limit the
speech signal to the frequency band 300‐3400
Hz.
Hz
8

9. SAMPLING PROCESS
s(t)
δ
A
t
Ts
Fourier series for impulse train :
S(t) = δ⁄TS + 2δ⁄TS (Cos 2π (t ⁄TS )+ Cos 2x2π (t ⁄ TS +….) 9

10. PAM OUTPUT SIGNALS
10

11. Nyquist’s Theorem says
:"If a band limited signal is sampled at
Pulse Code Modulation (PCM)
regular intervals of time and at a rate
equal to or more than twice the highest
Codec technique signal frequency in the band, then the
sample contains all the information of
the original signal." PCM actually uses
Voice Bandwidth = 8000 samples/sec since cutoff not sharp.
300 Hz to 3400 Hz
Analog Audio Source Sampling Stage
= Sample fS ≥ 2fm
Height of sampled signal above /
below the base line is converted 8 kHz (8,000 Samples/Sec)
to a binary value 11

12. The choice of sampling frequency, fs must follow the sampling theorem to
overcome the problem of aliasing and loss of information.The spectrum of the
sampled signal has sidebands fs ± fm , 2fs ± fm , 3fs ± fm and so on.
Shannon sampling
( ) Sampling eque cy
(a) S p g frequency=> fs1 < 2fm (max)
f theorem=> fs ≥ 2fm
th >
ms(f) Aliasing Nyquist frequency
fs = 2fm= fN
f A bandlimited signal that
fm fs1 2fs1 3fs1 has a maximum
f q
frequency, fmax can be
y,
regenerated from the
(b) Sampling frequency=> fs2 > 2fm (max) sampled signal if it is
ms(f) sampled at a rate of at
least 2fmax .
f
fm fs2 2fs2
f 3fs2
f
12

13. m(t)
Information signal
t
s(t)
Pulse signal
t
Ts
Sampled signal (PAM)
p g ( )
ms(t) ms(t)
t t
Ts Ts
Natural Sampling Flat‐top Sampling
13

14. PULSE AMPLITUDE MODULATED SIGNAL
NATURAL TOP
SAMPLING
CLOCK
The FET is the switch used as a sampling gate.
When the FET is on, the analog voltage is shorted to ground; when off,
the FET is essentially open, so that the analog signal sample appears at
the output.
Op-amp 1 is a noninverting amplifier that isolates the analog input
channel from the switching function.
14

15. FLAT-TOP SAMPLING
HIGH FANOUT
OP
AMP-2
clock SAMPLED & HOLD CIRCUIT
15

16. sample-and-hold circuit.
As seen in Figure, the instantaneous amplitude
of the analog (voice) signal is held as a constant
charge on a capacitor for the duration of the
sampling period Ts.
Op-amp 2 is a high input-impedance voltage
follower capable of driving low-impedance loads
(high “fanout”).
The resistor R is used to limit the output current
of op-amp 1 when the FET is “on” and provides
a voltage division with rd of the FET. (rd, the
drain-to-source resistance, is low but not zero)
d i t i t i l b t t )

17. 4.3.1 Difference in Sampling Methods
ms(t)
Natural Sampling
t
Ideal Sampling Flat-top Sampling
• In every sampling methods, the pulse amplitude is directly proportional to the
amplitude of the information signal
• Practically, an ideal sampling is difficult to generate
• However, by using an ideal and natural sampling, noise can be eliminated, which
is not the case for flat‐top sampling
17

18. Quantization
The output of a sampler is still continuous in amplitude.
Each sample can take on any value e.g. 3.752, 0.001, etc.
The number of possible values is infinite.
To transmit as a digital signal we must restrict the number of
possible values.
Quantization is the process of “rounding off” a sample according to
some rule.
E.g. suppose we must round to the nearest tenth, then:
3.752 ‐‐> 3.8 0.001 ‐‐> 0
Eeng 360 18

19. QUANTIZING POSITIVE
QUANTIZING‐POSITIVE SIGNAL
19

20. QUANTIZING ‐ SIGNAL WITH + Ve & ‐ Ve VALUES
20

21. 4.6.3 UNIFORM QUANTIZATION
Uniform quantization is a quantization process with a uniform (fixed) quantization
interval.
Example : n = 3 , L = 8 , signal +5 V ; => Vk = 1.25 V . Bit rate: fb
=nf s
Quantization level & Quantized Sampled signal
binary representation value
+5.0V
Leve l 7 : 111 4.375V 4.3V
Level 6 : 110 3.125V
1.9V
Level 5 : 101 1.875V 1.9V
Level 4 : 100 0.625V
t
Level 3 : 011 -0.625V
Level 2 : 010 -1.875V
Level 1 : 001 -3.125V -3.2V
Level
L l 0 : 000 -4.375V
-4 375V -4.5V
4 5V
-5.0V
21

22. 4.6.3.2 Quantization error
Quantization error (Qe) is also called Quantization noise (Qn) . And its maximum
magnitude is one half of the voltage of the minimum step size .
May add to or substract from the
actual signal
22

23. 4.6.3.2 Quantization error
23

24. Example : Uniform Quantization error
Binary Input voltage Input voltage range: –14 mV to
number range (mV) +14 mV
1 11 10 to 14
Qn = LSB voltage /2 = qi /2
g
1 10 6 to 10
1 01 2 to 6 ± 14 mV = 28 mV with 8 steps and 8 codes.
1 00 0 to 2 Therefore Qn = 28/8 = 3.5 mV.
0 00 ‐2 to 0
Therefore : Qn= 3.5 mV / 2 = 1.75 mV
0 01 ‐6 to ‐2
0 10 ‐10 to ‐6 SNRq = [1.76 + 6.02n] dB
0 11 ‐14 to ‐10 Noise from quantization error can be reduced by
increasing the quantization level i.e increase n.
24

25. Pulse Code Modulation - Analog to Digital Conversion
Quantizing Noise – sampling is not perfect
- the analog value may not correspond exactly
A-Law (Europe) to a binary value
Output
100100111011001
Stage 1
µ-Law (USA–Japan) Quantizing Stage
25

26. Non uniform quantization
companding
26

27. ENCODING CURVE WITH COMPRESSION 8 BIT CODE
27

28. 2 Popular companding system (standardized by ITU)
• EUROPE => A ‐ Law
• USA/NORTH AMERICA => µ ‐ Law
1+ log(Ax) 1
 1+ logA for 〈 x〈1
 A
y=
Ax 1
 for
f 0〈 x〈
 1+ logA
 A
A ‐ compressor paramater. Usually the
ll h
value of A is 87.6.
28

29. USA/NORTH AMERICA => µ ‐ Law
µ Law is a standard compress‐
expand that is used in America and
Japan. The value of µ used is 255 (8
bit).
log( 1 + µ x )
y =
log (1 + µ )
For both laws, the values of x and y
refers t th equation below:
f to the ti b l
Ei Eo
x= y =
E i ( mak ) E o ( mak )
29

30. Example : PCM‐System
PCM‐
Frame structure and Timing : European standard PCM system : E Line
488 ns Bit duration
8 bits per
time slot
3.9 µs
3.9 µs
30 signal + 2 control = 32 channels = 1 frame
125 µs
125 µs Signalling & synchronization
2 ms
Duration of multiframe 16 frames = 1 multiframe
(a) bits per time slot (b) time slots per frame (c) frames per multiframe
30

31. E1 CAS Transmission Format
ITU‐T Rec. G.704
Multiframe (16 frames)
Frame 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Frame 0 (32 Time Slots) Frame 1 (32 Time Slots)
Time Slot 0 1 2 3 4 5 6 7 8 910 12 14 16 18 20 22 24 26 28 30 0 1 2 3 4 5 6 7 8 910 12 14 16 18 20 22 24 26 28 30
11 13 15 17 19 21 23 25 27 29 31 11 13 15 17 19 21 23 25 27 29 31
Time Slot 0
Time Slot 1 Speech Time Slot 16 Speech Time Slot 0 Speech Time Slot 16 Speech
(8 bits)
Speech (Ch 1) Ch 1 15
(Ch. Ch. 1-15 (8 bits) Ch. 16-30
Ch 16 30 (8 bits) Ch. 1-15
Ch 1 15 Signalling Bits Ch. 16-30
Ch 16 30
1 1 1 1 1 1 1 1 LSB 11111111
X0011011 0 0 0 0X0XX X1 0XXXXX
00000000 Fr. 0 0 Ch. 0 0 0 0
0 0 Ch.
Multi-
Frame Changes to 1 on Changes to 1 on
Frame A BCD A BCD
Alignment loss of distant loss of distant frame
Alignment
Word Word multiframe (remote alarm) 1 1 16
Not-Frame 2 2 17
alignment word
3 3 18
• Time Slot 16 : Frames 2 through 15 are the same as frame 1 : : :
15 15 30
• Time Slot 0: Even number frames 2 through 14 are the same as frame 0
• Time Slot 0: Odd number frames 3 through 15 are the same as frame 1
1 = bit set to 1 0 = bit set to 0
1/0 = speech / signalling (varying data) X = unassigned bit (normally set to 1)

32. PDH E1 signal PCM30 basic frame
0 1 2 15 16 17 31
voice voice voice SIG voice voice
1 2 15 16 30
t
ca. 3,9 µs
1 2 3 4 5 6 7 8
Bit numbering
32 x 8 = 256 bit
Bit No. 125 µs
12345678 Bit No. 1 2 3 4 5 6 7 8
value X0 0 1 1 0 1 1 Value X1 Y Y Y 1 1 1
Frame alignment Message
Bit 1, X Used in Bit 1 X Used in international connections
international Bit 3 Y=1 FRAME SYNCHRONISATION
connections,
ti Bit 4 Y=1 HIGH ERROR DENSITY
Bit 3,4,5 111 Urgent alarm
FAW :‐0011011
Bit 6‐8 111 Reserved for national options
32

34. PCM – 32 channels (30 signals + 2 control)
Frame structure and timing
Number of channel = 32
Number of bits in one time slot = 8
32 channels = 1 frame
Number of bits in a frame = 32 x 8 = 256 bits
This frame must be transmitted within the sampling period and thus 8
x 103 frames are transmitted per second
second.
Therefore :
Transmission rate = 8 x 103 x 256 = 2 048 Mb/
T i i t 2.048 Mb/s
Bit duration = 1 / 2.048 x 106 = 488 ns
Duration of a time slot = 8 x 488 ns = 3.9 µs
µ
Duration of a frame = 32 x 3.9 µs = 125 µs => (= 1 / 8 kHz = 125 µs)
Duration of a multi frame = 16 x 125 µ s = 2 ms
34

35. PDH E1 signal
European digital signal 1
PCM30 (Puls Code Modulation, 30 voice channels)
G.703, G.704, G.732 (ITU recommendations)
PDH basic system (Plesiochronous Digital Hierarchy)
Features
Time multiplex
Bit rate 2,048 Mbit/s ±50 ppm
32 channels with 64 kbit/s each
30 voice channels 1 synchronisation/message, 1 signalling
channels, synchronisation/message
75 Ω coax or 120 Ω symmetrical twisted pair
Rectangular pulses, HDB3 line coding
35

36. Bit rate for PCM transmission
Telephone Europe bit rate(Mb/s) Telephone North America bit
channel channel rate(Mb/s)
30 2.048 24 1.544
120 8.448 48 3.152
480 34.368 96 6.321
1920 139.264 672 44.736
7680 565.148 4032 274.176
SDH 2.5Gb/s
North American standard (NAS) : µ-Law
European standard : A‐Law For every 24 sample, 1 bit is added for
synchronization
30 + 2 control channel = 32
∴ For 24 sample => 24 x 8 bit/sample + 1 bit
Bit rate 32 x 8 bit/sample x 8000 sample/s
rate= = 193 bits
bi
= 2.048 Mb/s ∴ Bit rate= 193 x 8000 = 1.544 Mb/s
Needs Multiplexing – Process of transmitting two or
more signals simultaneously
36

37. PDH Hierarchy
E1 E2 E3 E4 (E5)
2.048 Mbit/s 8.448 Mbit/s 34.368 Mbit/s 139.264 Mbit/s 565.148
Mbit/s
DIV
PCM
E2
DSMX 2/8
64k/2M E3
8/34
LE2 E4
34/140
MStD E5
140/565
37

38. SIGNAL :‐
:
• PLESIOCHRONOUS SIGNAL
• SIGNALS WHOSE CLOCK CAN VARRY
INDEPENDENT OF ONE ANOTHER BUT THE
RANGE OF SIGNAL VARIATION IS RESTRICTED
WITHIN CERTAIN LIMITS
LIMITS.
• Synchronous Signal
• Asynchronous Signal

39. MULTIPLEXING OF SYNCHRONOUS
DIGITAL SIGNALS
Block interleaving :
g
Bunch of information taken at a time from each
tributary and fed to main multiplex output stream.
The memory required will b very l
h d ll be large.
Bit interleaving :
A bit of i f
f information t k at ti
ti taken t time ffrom each t ib t
h tributary
and fed to main multiplex output stream in cyclic
order, a very small memory is required.
, y y q

40. Justification
• In general, incoming tributaries have
general
independent clocks. In that case, it is
inevitable that clock rate of a tributary and the
(divided) clock rate of the multiplexer (in
second order TDM it is 8448/4 = 2112 KHz)
TDM,
are not the same. Without any precautions,
the result will be Slip
Slip.

41. MULTIPLEXING OF ASYNCHRONOUS
SIGNAL
• Positive justification : Common synchronization bit
j y
rate offered at each tributary is higher than the bit
rate of individual tributary.
• Positive‐negative justification : Common
f
synchronization bit rate offers is equal to the
nominal value.
• Negative justification : Common synchronization
bit rate offered is less than the nominal value.

42. PDH E2 signal Frame structure
Frame alignment pattern Alarms
1111010000UN
Justification control bits Justification bits
1 bit per channel and frame 1 bit per ch. and frame
(transmitted 3 times) no stuffing: information
0=no stuffing; 1=stuffing stuffing: fixed value
1234 1234 12345678
1..12 13..212 5..212 5..212 9..212
Block 1 Block 2 Block 3 Block 4
200 info bits 208 info bits 208 info bits 204-208 info bits
848 bit
100,38 µs
42

43. • Four bit stream of 2048 Kb/s are multiplexed. The resulting bit
stream of 8448 Kb/s can be thought of being composed as
/ g g p
follows :‐ Per tributary=8448÷4=2112Kb/s
• No of frame per second =8448kb/s÷848=9962≈10000
• Nominal bit rate : 2048 Kb/s
• Frame alignment i f
F li t information P t ib t
ti Per tributary: 30 Kb/
Kb/s
• Justification control digits : 30 Kb/s
• Sub total : 2108 Kb/s
• Justification digits : 2112‐2108= 4 Kb/s used to
allow over speed
• Justification rate per frame and E1 signal 0.42 bit

44. PDH E3 signal Frame structure
Frame alignment pattern Alarms
1 1 1 1 0 1 0 0 0 0 UN
Justification control bits Justification bits
1 bit per channel and frame 1 bit per ch. and frame
(transmitted 3 times) no stuffing: information
0=no stuffing; 1=stuffing stuffing: fixed value
1234 1234 12345678
1..12 13..384 5..384 5..384 9..384
Block 1 Block 2 Block 3 Block 4
372 info bits 380 info bits 380 info bits 376-380 info bits
1536 bit
44,6927 µs
44

45. PDH E4 signal Frame structure
Alarms
Frame alignment pattern Data communication channel
1 1 1 1 1 0 1 0 0 0 0 0 D N Y1 Y2
Justification control bits Justification bits
1 bit per channel and frame 1 bit per ch. and frame
(transmitted 5 times) no stuffing: information
0=no stuffing; 1=stuffing stuffing: fixed value
1234 12345678
1..16 17..488 5..488 9..488
Block 1 Block 2, 3, 4, 5 Block 6
472 info bits je 484 info bits 480 - 484 info bits
2928 bit
21,024 µs
45

46. Specification at Output Port
E1 E2 E3 E4 E5
Bit rate in Mbit 2.048 8.448 34.368 139.264 565.148
Clock tolerance ±50PPM ±30PPM ±20PPM ±15PPM ±5PPM
Frame length in bits 256 848 1536 1928
Stuffing rate per frame 0.42 0.4357 0.4192
Impedance in Ω 120/ 75 75 75 75
75
Nominal pulse width 244 ns 59ns 14.55ns
Line code HDB–3 HDB–3 HDB–3 CMI

47. What is SDH?
• The basis o Sy c o ous Digital Hierarchy (S )
e bas s of Synchronous g ta e a c y (SDH)
is synchronous multiplexing ‐ data from multiple
tributary sources is byte interleaved.
• In SDH the multiplexed channels are in fixed
locations relative to the framing byte.
• De‐multiplexing is achieved by gating out the
required bytes from the digital stream.
• Thi allows a single channel t b ‘d
This ll i l h l to be ‘dropped’ f
d’ from
the data stream without de‐multiplexing
intermediate rates as is required in PDH
PDH.
1/13/2012

48. Multiplexing Processes
– Multiplexing is composed of various processes:
• Mapping
–Tributaries adapted into Virtual Containers
(VC) by adding stuffing and POH
• Aligning
–Pointer is added to locate the VC inside an AU
or TU
• Multiplexing
–Interleaving the bytes of multiple paths
Interleaving
• Stuffing
–Adding up the fixed stuff bits to compensate
g p p
for frequency variances

49. TRANSPORT OF PDH PAYLOAD
SDH is essentially a transport mechanism for carrying a
large number of PDH payloads.
• A mechanism is required to map PDH rates into the STM
frame. This function is performed by the container (C).
• A PDH channel must be synchronized before it can be
mapped into a container.
• The synchronizer adapts the rate of an incoming PDH signal
to SDH rate.
SDH and non synchronous signal
• At the PDH/SDH boundary Bit stuffing is performed
when the PDH signal is mapped into its container
container.
1/13/2012

50. STM N
STM‐N frame
270 x N Columns
9xN
Columns
STM-N VC capacity
9
Rows
125 µsec
Section
Overhead
1/13/2012

51. SDH Rates
• SDH is a transport hierarchy based on
multiples of 155.52 Mbit/s.
The basic unit of SDH is STM 1:
STM‐1:
STM‐1 = 155.52 Mbit/s
STM‐4 622 08
STM 4 = 622.08 Mbit/s
STM‐16 = 2588.32 Mbit/s
STM‐64 = 9953.28 Mbit/s /
• Each rate is an exact multiple of the lower rate therefore the
hierarchy is synchronous.
1/13/2012

52. Mapping Hierarchy
STS-3N
x1 STS-3c BULK
xN
C-4 139 Mbit/s
STM-N AUG AU-4 VC-4 ATM
x3
x1
x3
TUG-3 TU-3 VC-3
x1
44 Mbit/s
STM-0 AUG AU-3 VC-3 C-3 34 Mbit/s
x7
7 DS3 BULK
STS-1
STS-1 x7
SPE
x1
TU-2 VC-2 C-2 6.3 Mbit/s
TUG-2
x3
VT
group TU-12 VC-12 C-12 2 Mbit/s
xN
Multiplexing x4
TU-11
TU 11 VC-11
VC 11 C-11 1.5 Mbit/s
C 11 1 5 Mbit/
Aligning VT-1.5
Mapping
1/13/2012

53. Synchronous & Asynchronous Transport of 2MBPS Signal.
1/13/2012

54. Pointer
4 Bytes
v1
V1 & v2 points
p
TU12
V5
v2
v5
VC-12
500 µsec
v3
1/13/2012

55. STM‐1 frame
270 bytes
RSOH 1 ….. 9 261Byte
3 rows
pointer Information
9 Rows
R
Payload
MSOH
5 rows
Transport 125 µs
overhead
Synchronous Payload Envelope
1/13/2012

56. STM 1
STM‐1 Section Overhead
A1 A1 A1 A2 A2 A2 J0 ∆ - media
dependent
R Section
R-Section
B1 ∆ ∆ E1 ∆ F1
Overhead
D1 ∆ ∆ D2 ∆ D3
AU pointer H1 H1* H1* H2 H2
H2* H2
H2* H3 H3 H3 H1
H1* = 10010011
B2 B2 B2 K1 K2 H2* = 11111111
D4 D5 D6
M-Section
Overhead D7 D8 D9
D10 D11 D12
national use
S1 M1 E2
1/13/2012

57. STM 0
STM‐0 Overheads
HO Path
Section Overhead Overhead
Framing Framing RS Trace Path Trace
A1 A2 J0 J1
R-Section BIP-8 Orderwire User Channel BIP-8
Overhead B1 E1 F1 B3
Data Com Data Com Data Com Signal Label
D1 D2 D3 C2
Path Status
AU pointer Pointer Pointer Pointer
G1
H1 H2 H3
BIP-8 APS APS User Channel
B2 K1 K2 F2
Multiframe
Data Com Data Com Data Com Indicator
M-Section D4 D5 D6 H4
Overhead Data Com Data Com Data Com User Channel
D7 D8 D9 F3
Data Com Data Com Data Com APS
D10 D11 D12 K3
Sync (REI) Orderwire Tandem
S1 (M1) E2 N1
1/13/2012

58. Payload Pointer
Payload Pointer marks
start of STM-1 VC 3 or
t t f STM 1 VC-3
VC-4
90 (VC-3) or 270 (VC-4) Columns
STM-1 Frame #1
H1 H2 H3...
9
Rows STM 1
STM-1
VC-3 or VC-4
STM-1 Frame #2 125 µsec
9
Rows
STM-1 VC-3 or VC-4
POH column
250 µsec
1/13/2012 Section
Overhead

59. Pointer Bytes (H1, H2) for AU‐3
Based Frames
B dF
– STM‐1 pointer bytes usage:
p y g
• 3 x AU‐3 bit streams should be located
10
1 2
271 273
3 4 5 6 7 8 9 268 269 270
STM-1
H1 H1 H1 H2 H2 H2
2430
Section
Overhead (SOH) 3 x AU 3 s
AU-3's
1 2 3 87 89 90
H1 H2
SPE
810
Path
Overhead (POH)

60. Overhead Layer Concepts
path
multiplex section multiplex section
regenerator regen. regen. regenerator
section section section section
ADM
TM REG or REG TM
DCS
path regen. section multipl. section regen. section path
termination termination termination termination termination
PTE = path terminating element
TM = terminal multiplexer
service (E1, E4..)
mapping
pp g REG = regenerator service (E1, E4..)
( , )
demapping ADM = add/drop multiplexer mapping
DCS = digital cross-connect system demapping
DXC= digital cross connect

61. Regenerator
– A regenerator simply extends the possible
distance and quality of a line by decomposing it
into multiple sections
• Replaces regenerator section overhead
• Multiplex section and path overhead is not altered

62. Add‐drop Multiplexer ‐ I.
– Add/drop multiplexer (ADM)
• Main element for configuring paths on top of line topologies
(point‐to‐point
(point to point or ring)
• Multiplexed channels may be dropped and added
• Special drop and repeat mode for broadcast and survivability
p p p y
• An ADM has at least 3 logical ports: 2 core and 1 or more add‐
drop Electrical
port
t
Optical port Optical port
• Ports have different roles
• No switching between the core ports
g p
• Switching only between the add‐drop and the core ports

63. Topology Basics

64. SDH RING TOPOLOGY

65. Uni
Uni‐ and Bi‐directional Routing
Bi directional
A A
A‐C
AC AC
A‐C
F B F B
C‐A
C‐A
E C E C
D D
Uni‐directional Ring Bi‐directional Ring
(1 fiber) (2 fibers)
– Only working traffic is shown
– Subnetwork (path) or multiplex section switching for
protection

66. Operations – Fiber Cut ‐ I.
– Protection dedicated ‐
head end bridge
– Failure interrupts A‐C A
working traffic
– Receiver at C detects
F B
failure
Protection
Traffic
Working g
Traffic
E C
Working
k
D traffic
selected

67. Operations – Fiber Cut ‐ II.
– Fiber cut recovery steps:
y p
• Tail end (receiver)
switches to protection A
traffic
• Only the
F B
receiving node
knows about Protection
the protection Traffic
switch Working g
Traffic
– No traffic lost E C
Protection
D traffic
selected

68. Standardization
– Basic APS operations are defined in ITU‐T G.783
ITU T
– USHR/P is originally not fully defined by ITU‐T
– Later defined in ITU T G 841 as general VC trail
ITU‐T G.841
protection switching independent of the
underlying topology
• USHR/P is called 1+1 unidirectional VC trail switching
(ring topology is only a special case) with dedicated
protection
– USHR/MS and other variants are more a
theoretical possibility than real products

69. Section 3 4
3.4
BSHR T l
Topology

70. Operations – Traffic Flow
– Duplex traffic between
p
two nodes goes through a
subset of ring links
– Minimum capacity equals
line rate (same as USHR/P A
maximum)
– Line rate must be an even F B
integer of STM‐1 for 2‐
fiber configurations
g
• Automatically fulfilled
E C
with newer standards
only working
D traffic shown

71. Maximum Bandwidth Capacity
– Each link represents half
p
of the line rate of STM‐1s
(i.e. 8 STM‐1s for an STM‐ A‐B
F‐A A
16)
– All traffic from a node A‐F B‐A
goes to adjacent F B
nodes
d Only
– Max. capacity = E‐F working
F‐E traffic C‐B B‐C
0.5 (line rate) x
( ) shown
number of nodes
E C
E‐D D‐C
D C‐D
D‐E

72. Extra Traffic
– Extra traffic utilizes
shared protection
bandwidth Working
– Extra traffic is not A Traffic
protected when a
failure occurs
F B
– Extra traffic could
be lost when a
failure of working Extra Traffic
in Protection
traffic occurs bandwidth
– Extra traffic is ONLY
available on a E C
BSHR/MS
D

73. Operations – Fiber Cut ‐ I.
– Failure interrupts A‐C and
p
C‐A traffic Fiber cut
– A and B detect failure
A
STM‐1#4
STM‐1#4
F B
Working
Traffic
E C
D

74. Operations – Fiber Cut ‐ II.
STM‐1#10 into STM‐1#4
– No dedicated protection
p Fiber cut
bandwidth ‐ only Loops
A
used when protection
required STM‐1#4
STM‐1#4 into into
– Only nodes next F STM‐1#10
B STM‐1#10
STM‐1#10 into
to the failure know STM‐1#4
about th
b t the Working
Traffic
protection switch
– No traffic lost
E C
D
Protection
Traffic

75. Path Protection Switching
R‐Section Payload
Overhead
VC
Path
Overhead
STM Info
Path controlling
Overhead protection
M‐Section switching
Overhead VC
Payload
– Conditions resulting in a protection switch:
• Loss of pointer, STM or VC AIS
• Excessive BIP errors for STM path, BIP errors for VC path
path

76. 1/13/2012 OFC SDE RTTC, BSNL,BHUBANESWAR 76