pdh technology
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By Ayodeji Morakinyo 1
PLESIOCHRONOUS DIGITAL HIERARCHY (PDH)
By Ayodeji Morakinyo
…At the Speed of Ideas
AGENDA
1. Introduction
2. Pulse Code Modulation
3. Time Division Multiplexing
By Ayodeji Morakinyo 2
4. PDH
5. ALU PDH Solutions
INTRODUCTION
In modern transmission systems, a particular wave characteristic
such as phase, frequency and amplitude is varied to achieve modulation
and then time, frequency, space or wavelength is used as a point of
reference for multiplexing several signals before sending them along a
transmission link.
By Ayodeji Morakinyo 3
Plesiochronous digital hierarchy (PDH) is one of the most widely used
transmission techniques. It employs the Pulse Code Modulation technique to attain
a basic data rate of 2Mbps (E1) consisting of 32 multiplexed base channels.
Analog Signal
This presentation, being the
output of a recently conducted study
by the presenter, will first consider the
pulse code modulation and time
division multiplexing techniques
before discussing the PDH technology.
By Ayodeji Morakinyo 4
It will also showcase some
PDH equipments with a focus on ALU
products.
PULSE CODE MODULATION
MODULATION
This is the technique by which information in their analog or digital forms
(usually baseband signals) are converted to RF signals that can be transmitted. In
modulation, a wave characteristic is varied such that the output conforms to a
desired pattern.
For instance, waves produced from the human vocal cords can be
modulated based on frequency (FM), amplitude (AM) or phase (PM). FM and AM are
By Ayodeji Morakinyo 5
modulated based on frequency (FM), amplitude (AM) or phase (PM). FM and AM are
mainly used in commercial radio broadcasting while phase modulation is employed in
applications like GPS receivers. Other ways of modulating information include: FSK,
PSK, ASK, OFSK, DBPSK etc.
Analogue signal transmission has relatively high susceptibility to EMI which
reduces the quality of signal transferred. To avoid this, the analogue signal is usually
digitized before transmission.
Pulse code modulation is a technique used to convert analogue signals to
their digital equivalent by characterizing the original signals in discrete pulses. To
achieve PCM modulation, the signals must be subjected to certain processes such as
sampling, quantizing and encoding.
Advantages of digital transmission over analogue method
By Ayodeji Morakinyo 6
•Error detection and correction
•Data integrity when transmitting over long distances
•Multiplexing of voice, video and digital data over one channel
•Larger bandwidth
•Easier to encrypt and compress data
•Reduced hardware cost
SAMPLING
This is the process of reconstructing the continuously changing analogue
signal into approximate samples which have a range of voltages that can be
referenced.
The sampled signals will have various amplitude at different time periods. A
signal range which must cover all possible input levels is chosen. For PCM, 8bits is
chosen for sampling the telephone circuit system.
The bit values sampled are representations of the voltage sampled at a
time. Each digit represents a power of 2.
By Ayodeji Morakinyo 7
The telephone system digitizes our voice signal for digital transmission
Full range of human hearing is within 20 – 20000Hz and the human voice
frequency occupies the ultra-low frequency band of the EM spectrum at 300 –
3400Hz.
So, how fast should we sample and obtain discrete values to prevent data loss and
aliasing?
By Ayodeji Morakinyo 8
QUANTIZATION
This involves the conversion of samples to discrete values. A comparator
compares the actual voltage to the reference (quantized) voltages.
000 010 100 110
001 011 101 111
By Ayodeji Morakinyo 9
From Nyquist Theorem,
Perfect reconstruction of a signal is possible when Fs is > twice the signal being
sampled, i.e. :
Fs= 2 x Fmax
Therefore, bandwidth allocation for single voice frequency transmission channel is
4KHz including guard bands.
Fs= 2 x Fmax = 2 x 4000Hz
Sampling frequency or rate = 8000Hz or 8KHz or 8000samples/bit. And, the time
interval between 2 consecutive samples is 125microsecondsinterval between 2 consecutive samples is 125microseconds
Since 8bits are used for PCM for telephone system, we will need 8 channels for the
8 quantized bits.
Therefore, 8KHz (or 8000samples/segment ) x 8bits/sample
= 64Kbit/s (or 64bits/segment)
By Ayodeji Morakinyo 10
ENCODING
This involves the introduction of additional transmission bits (ones and
zeros) to the quantized values by an encoder to ensure proper sending of the digital
signal.
Common characteristics of transmission codes are:
•To increase possible transmission distance, the average DC line component of the
code has to be zero volt
•To recover the bit clock, frequent transitions of the digital signal must be provided
Examples of the transmission coding types include but are not limited to:Examples of the transmission coding types include but are not limited to:
HDB3, AMI, RZ, NRZ and CMI coding.
In HDB3, where there more than 3 zeros consecutively, a violation pulse is
added by the encoder and the decoder deletes it at the receiving end.
By Ayodeji Morakinyo 11
In AMI, the encoder represents a “0” by zero volt and a “1” by an alternate
positive or negative pulse.
In NRZ, a “0” is represented by a negative pulse and a “1” is represented by
a positive pulse.
In CMI, a “0” is represented by half a positive and half a negative pulse
within one time interval. A “1” is represented by a positive or negative pulse for a
full unit time interval.
By Ayodeji Morakinyo 12
TIME DIVISION MULTIPLEXING
MULTIPLEXING
This involves the combination of two or more signals for transmission
along a single channel. This is done to maximise bandwidth and save overall cost
when huge amounts of information are involved.
Data from Combined signal
De
mu
x Separation
By Ayodeji Morakinyo 13M
ux
Data from
difference
sources
Combined signal
De
mu
x Separation
back into
different
components
Multiplexing can be of different types:
TDM, FDM, SDM and WDM. In this presentation, we will discuss TDM as a technique
that is compatible with PDH technology.
TIME DIVISION MULTIPLEXING
In TDM, multiplexing is a function of time slot. Two or more bit streams or
signals are transferred simultaneously as sub-channels in one communication
channel, but are physically taking turns on the channel. The time domain is divided
into several recurrent timeslots of fixed length, one for each sub-channel. A sample
byte or data block of sub-channel 1 is transmitted during timeslot 1, sub-channel 2
during timeslot 2, etc.
A time slot is an interval within which an 8-bit PCM word is transmitted and
a frame is a set of consecutive time slots.
By Ayodeji Morakinyo 14
TDM can be performed through Bit or Byte Interleaving. In Byte interleaved
type, the input signal occupies one complete byte of the input signal while in bit
interleaved format, one bit of input signal occupies a time slot.
For example,
A1 A2 A3 A4 A5 A6 A7 A8
B1 B2 B3 B4 B5 B6 B7 B8
C1 C2 C3 C4 C5 C6 C7 C8
TDM Multiplexer
A1 A2 A3 A4 A5 A6 A7 A8
Byte Interleaving
Sub-
channel A
Sub-
channel B
Sub-
1 byte of 1 channel per time slot
or
C1 C2 C3 C4 C5 C6 C7 C8
D1 D2 D3 D4 D5 D6 D7 D8
TDM Multiplexer
A1 B1 C1 D1 E2 F2 G2 H2
H1 H2 H3 H4 H5 H6 H7 H8
.
.
.
Bit Interleaving
8 bits
8 bits of 8 channels per time slot
Sub-
channel C
Sub-
channel D
Sub-
channel H
8 bytes per sub-channel
By Ayodeji Morakinyo 15
PLESIOCHRONOUS DIGITAL HIERARCHY
“Plesiochronous” means, almost the same. Plesiochronous signals are
signals that have the same nominal frequency but are not synchronised to one
another. This is because they originate from different multiplexers which have
different clocking.
As such, in PDH, the rise and fall time of the pulses in each tributary (or
bit stream) do not coincide unlike in SDH where all the tributaries have same clock
frequency and are synchronised to a master clock.
By Ayodeji Morakinyo 16
PDH Hierarchy in Japan, North America and Europe
By Ayodeji Morakinyo 17
Digital MUX
Level
No.of 64Kb/s
Channels
North America
(Mbits/s)
Europe
(Mbits/s)
Japan
(Mbits/s)
0 1 0.064 0.064 0.064
1 24 1.544 1.544
30 2.048
48 3.152 3.152
2 96 6.312 6.312
120 8.448
PDH MUX Levels
By Ayodeji Morakinyo 18
120 8.448
3 480 34.368 32.064
672 44.376
1344 91.053
1440 97.728
4 1920 139.264
4032 274.176
5760 564.992 397.200
BIT/PULSE STUFFING
In PDH, the small variations in frequency about the nominal value must be
accounted for when multiplexing four tributaries to the higher order level on the
hierarchy. To achieve this, a process termed stuffing must occur.
Stuffing involves intentionally making the output bit rate of a channel higher
than the input by inserting additional bits in the incoming bit stream. Consequently,
the output channel contains all the input data plus variable number of “stuffed bits”
that are NOT part of the incoming subscriber information.
By Ayodeji Morakinyo 19
-- --Higher
Order
Multiplexer
Frame no.1
Lower Bit Rate
Higher Bit Rate
Stuffing
Control bit Stuffing
bit is a
data bit
Stuffing bit is
a stuff bit
Frame no: 2
PDH Frame
The basic frame rate for PDH (using the European standard) is 2.048Mbps
where 32 voice channels are used. But only 30 channels are utilized for communication
because one is used for signalling and another for synchronisation.
By Ayodeji Morakinyo 20
By Ayodeji Morakinyo 21
A multiframe is composed of 16 frames and a sub-multiframe is
composed of 8 frames. The first time slot is used for frame alignment or control
while timeslot 16 is used for signalling (if not, it can be used to carry user
information). Each frame has 32bytes.
PDH Frame period is 125µs then,
1byte is a 8bit/125µs = 64Kbit/s
And the transmission rate is:
(32channel X 8bit/channel) X 125µs = 2.048Mbps
FRAME ALIGNMENT SIGNAL (FAS)
•allows targeting of synchronisation to find beginning of the frame
•comprises the 7bits of the first time slot of each numbered frame
which are responsible for the CRC (C1,C2,C3,C4 bits) or CRC-
By Ayodeji Morakinyo 22
which are responsible for the CRC (C1,C2,C3,C4 bits) or CRC-
4multiframe and E bits
•the CRC-4 bits detect block errors and the E bits indicate the block
errors
•FAS = 0011011
NON-FRAME ALIGNMENT SIGNAL (NFAS)
The second bit of NFAS is “1” and it is
used to avoid coincidences with the FAS.
The “A” bits (distance alarm indication
bits) are used for alarm management. They
indicate power fault, LOS, LOF and codec fault.
By Ayodeji Morakinyo 23
The “S” bits (spare bits) are reserved
space for network operator’s use i.e. application,
monitoring and maintenance of performance. If
the S or spare bits are not used, they should be
set to 1.
ERRORS
Common errors associated with PDH transmission include the LOF which is
indicated via an AIS and the REBE which is detected by the CRC4 bits.
By Ayodeji Morakinyo 24
Other Associated Errors
By Ayodeji Morakinyo 25
Types:
1. CAS which uses the multiframe structure (TS1-TS15 and
TS17-TS30) as predefined positions to carry the
SIGNALLING CHANNEL
This is used to exchange information between LEs. It uses the timeslot 16 of
the 2Mbps frame where Si is a four bits (a1,a2,a3,a4 ) channel and i values go from 1 to 30
per channel.
By Ayodeji Morakinyo 26
TS17-TS30) as predefined positions to carry the
signalling multiframe alignment signal.
2. CCS which is a byte-oriented responsible for carrying
signalling information for several communications.
There are no predefined positions for the
communication channels .
SYNCHRONIZATION
When multiplexing to the basic rate, synchronisation is put in place by the
PCM MUX through bit interleaving and if they connected to the same master clock, the
signals become synchronous.
But when multiplexing to higher rates (second, third and fourth orders), the
MUXes must provide a mechanism for accommodating rate impairments.
This mechanism is called justification/stuffing and the bits that perform this
are the justification bits and justification control bits (JB and JC bits).
By Ayodeji Morakinyo 27
are the justification bits and justification control bits (JB and JC bits).
•If bits Jik=1 then, Ri is justification, no information
•If bits Jik= 0 then, Ri contains tributary information
•If not all are 0s or 1s, then decision is based on majority count of Jik
Where:
By Ayodeji Morakinyo 28
Where:
A = alarm indication bit
R = reserved for internal use
T = bits from tributary i
JC = justification control bit for tributary i
JB = justification bit for tributary i
LIMITATIONS OF PDH
•Lack of efficiency which makes it necessary to fully demultiplex before low
tributaries can be extracted from high order aggregates.
•Insufficient capacity for network management and monitoring because the system is
limited to a few bits (NFAS, NMFAS).
•There is no standardised definition of PDH bit rates greater than 140 Mbp e.g.
564.992Mbps.
By Ayodeji Morakinyo 29
564.992Mbps.
•Every clock is different and therefore synchronisation errors show up.
•Not Transparent (lack of compatibility between European, Japanese and North
American standards.
•Protection schemes are not available hence, ring, and hub configurations are not
possible.
ALU PDH SOLUTIONS
9400 AWY
The 9400AWY is ideal for short-haul digital transmissions in high density
mobile networks especially 2G, 2.5G, 3G and Wimax. It utilizes the utility networks,
regional & local traffic systems and private WANs and LANs.
Features:
• Indoor unit (IDU) supports up to 32 × E1 traffic
interfaces
By Ayodeji Morakinyo 30
9400AWY9400AWY
interfaces
• Outdoor unit (ODU) supports 4- and 16-quadrature
analogue multiplier (QAM); software upgradeable as
needed
• One ODU version exists with 32 Mb/s capacity/4-
QAM only
• Can combine with the Alcatel-Lucent 9500
MPR/MXC and 9600 LSY/USY families in the same
network
More Features:
• Provides output power agility: automatic
transmit power control (ATPC) and
static/reactive TPC (RTPC) in all frequency bands
• Offers capacity agility to support up to 32 ×
E1, 1 × E3, or 4 Ethernet ports, with a maximum
capacity of up to 64 Mb/s, including mixed
configurations such as 16 × E1 and 2 Ethernet
ports
• Provides flexible TDM/LAN interfaces
•Software configurable, with easy
By Ayodeji Morakinyo 31
•Software configurable, with easy
installation/setup and multilevel loopback/test
facilities
• Offers comprehensive application options e.g.
GSM/GPRS/UMTS, Wireless data access,
WAN/LAN data networks, PABX, ATM,
videoconferencing, Utility networks: pipelines,
electricity,
railways, municipalities.
9400AWY Configurations
In 1+0: 1U optimised Main IDU
minimum configuration 8E1/16Mbps or 16E1/32Mbps
modular slot for expansion up to 32E1/64Mbps
common to all frequency bands
By Ayodeji Morakinyo 32
In 1+1: 1U complete Extension IDU
AWY offers both full protection and radio protection
AWY Indoor can be replaced for repair without traffic impact
common to all frequency bands
ODU V1
32/64Mb
ODU V2
32/64MbODU V1
32/64Mb
ODU V2
32/64Mb
32/64 Mb max on the air
Compatibility
By Ayodeji Morakinyo 33
9500 MXC
The 9500 MXC provides solution for SDH and “super PDH” applications
going up to 93 E1/100DS1, higher flexibility is given by the integrated cross
connection capabilities. Additionally, the product fits well for fixed applications
including DSL and WiMAX backhauling due to its multiple interfaces: PDH, SDH and
Ethernet with integrated layer-2 switching.
Features
•Cost-effective wireless solution for High
Capacity applications up to 2xSTM-1.
By Ayodeji Morakinyo 34
Capacity applications up to 2xSTM-1.
•High Capacity Ethernet transport with
embedded L2 switch
•Intelligent Indoor nodal unit supports up to
six ODUs
•Universal ODUs capacity and modulation
independent
•9500 MXC supports 1+1 protected configurations including Hot Stand-by and
diversity configurations.
•For additional protection of INU functions an NPC can be added to provide power
supply and NCC control redundancy
•Choice of operation as SDH or SuperPDH radio via
software.
•NxE1 rates up to 93xE1 over a single 28MHz carrier
•Choice of E1, E3, STM-1, Ethernet and Gigabit Ethernet
By Ayodeji Morakinyo 35
•Choice of E1, E3, STM-1, Ethernet and Gigabit Ethernet
customer interfaces.
•Software-configurable traffic routing, without local
cabling.
•9500 MXC Craft Terminal, an advanced Java-based
maintenance tool presents local and remote node status
with performance monitoring, configuration control and
diagnostics
The INU is available in a standard 1RU and extended 2RU shelf (INUe) to support
up to 3 outdoor units (ODUs) or 6 ODUs respectively.
The wireless node architecture is enabled by the Intelligent Node Unit, or INU. Its
modular design supports either a simple terminal, or a more complex node,
through a variety of hot-swappable plug-in cards.
By Ayodeji Morakinyo 36
INUe
INU unit
By Ayodeji Morakinyo 37
INUe unit
9500 MPR
9500 MPR is a Service
Aggregator. This means that it is able to
gather different kinds of traffic sources
and to use ETHERNET as a convergence
layer for all of them for uplink into a
Packet Network.
MXC and MPR share the same Outdoor Unit and IF coax cable, allowing
when needed , a smooth and less expensive migration in field, from TDM to packet
(IP), by simply replacing the Indoor unit.
By Ayodeji Morakinyo 38
The MSS is used to interface the tributaries, to perform service while the
ODU is used to convert the modulated IF signal into RF and allow the transmission in
the air by means of an integrated antenna (directly connected to the ODU) as in the
slide or a not integrated antenna (connected to the ODU with a flex twist/waveguide
section).
9500 MPR is made of two separated parts (split-mount): an indoor part
called MSS (Microwave Service Switch) and an external one called ODU.
To integrate TDM, IP and microwave technologies, the Alcatel-Lucent 9500
MPR platform includes three main components.
Lack of Synchronization could mean call-dropping in handover cases;
avoiding this situation is obviously mandatory in order to improve QoS and
Customer Satisfaction.
By Ayodeji Morakinyo 39
The Microwave Packet Transport Unit — High Capacity, Long Haul (MPT-
HL) simplifies the critical part of a microwave system, using the latest RF and modem
technology. It provides two RF slots in 2.5 rack units of space in 1+0, 1+1 Space
Diversity/Frequency Diversity (SD/FD), and 2+0 installations. The MPT-HL is the first
all-packet, all-indoor nodal microwave transmission system.
Feature 9500 MPR 9500 MXC 9400 AWY
Mixed Traffic (TDM + Ethernet) Yes Yes Yes
Point-to-point configuration Yes Yes Yes
Node configuration Yes (*) Yes No
Native Packet Transport (over Air) Yes No No
Adaptive Modulation Yes No No
Internal cross-connections Yes Yes No
9400 AWY – 9500 MXC – 9500 MPR feature comparison
By Ayodeji Morakinyo 40
Internal cross-connections Yes Yes No
End-to-end traffic management Yes No No
QoS management Yes Yes Yes
End-to-end QoS management Yes No No
NE pre-configuration (Off-line tool) Yes (*) No Yes (*)
AT
THE
END OF PRESENTATION
Thank you
By Ayodeji Morakinyo 41
THE
SPEED
OF
IDEAS
ACRONYMS
ALU = Alcatel-Lucent
AMI = Alternate Mark Inversion
ASK = Amplitude Shift Keyed Modulation
ATM = Asynchronous Transfer Module
AWY = Asynchronous Wireless Second Generation
Codec = Coder/Decoder
By Ayodeji Morakinyo 42
Codec = Coder/Decoder
CCS = Common Channel Signal
CRC = Cyclic Redundancy Check
CRC4 = Cyclic Redundancy Check 4 bits
DAC = Digital-Analogue Converter
DBPSK = Differential Binary Phase Shift keyed Modulation
DC = Direct Current
Demux = demultiplexer
E1 = E-carrier signal level 1
EM = Electromagnetism or Electromagnetic
EMI = Electromagnetic Interference
FDM = Frequency Division Multiplexing
Fs = Sampling Frequency
GPRS = General Packet Radio Service
GPS = Global Positioning System
By Ayodeji Morakinyo 43
GPS = Global Positioning System
GSM = Global System for Mobile Communications
HDB3 = High Density Bipolar Excess 3
IDU = Indoor Unit
IF = Intermediate Frequency
INUe = Intelligent Node Unit extension
IP = Internet Protocol
LAN = Local Area Network
LE = Local Exchange
LSY = Long-Haul Second Year/Generation
MPR = Microwave Packet Radio
MUX = Multiplexer
MXC = Microwave Cross-Connect
NCC = Node controller Card
NPC = Node Protection Card
By Ayodeji Morakinyo 44
NPC = Node Protection Card
NMFAS = Non-Multiframe Alignment Signal
NRZ = Non-Return to Zero
OFSK = Orthogonal Frequency Shift Keyed Modulation
PABX = Private Automatic Branch Exchange
PSK = Phase Shift Keyed Modulation
QoS = Quality of Service
RAC = Radio Access Card
RF = Radio Frequency
RZ = Return to Zero
SDH = Synchronous Digital Hierarchy
SDM = Space Division Multiplexing
STM = Synchronous Transport Module
TDM = Time Division Multiplexing
TS = Time Slot
By Ayodeji Morakinyo 45
TS = Time Slot
UMTS = Universal Mobile Telecommunications System
USY = Ultra Long-Haul Second Year (Second Generation)
WAN = Wide Area Network
WDM = Wave Division Multiplexing
WiMAX = Wireless Interoperability for Microwave Access
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