Technologies used in
telecommunication networks
PDH
:-PLESIOCHRONOUS DIGITAL
HIERARCHY.
A TECHNOLOGY USED IN
TELECOMMUNICATIONS NETWORK
TO TRANSPORT LARGE QUANTITY
OF DATA OVER DIGITAL
TRANSPORT EQUIPMENT SUCH AS
FIBRE OPTIC AND MICROWAVE
RADIO WAVE SYSTEMS.
 THE
TERM “PLESIOCHRONOUS” IS
DERIVED FROM Greek plesio which
means near, and chronous, time.
 IT MEANS THAT PDH NETWORKS RUN
IN A STATE WHERE DIFFERENT PARTS
OF THE NETWORK ARE ALMOST, BUT
NOT QUITE PERFECTLY
SYNCHRONISED.
 SENDING
A LARGE QUANTITY OF DATA
ON FIBRE OPTIC TRANSMISSION
SYSTEM.
 TRANSMISSION AND RECEPTION ARE
SYNCHRONIZED BUT TIMING IS NOT.
 THE CHANNEL CLOCKS ARE DERIVED
FROM DIFFERENT MASTER CLOCKS
WHOSE RANGE IS SPECIFIED TO LIE
WITHIN CERTAIN LIMITS. THE
MULTIPLEXED SIGNAL IS CALLED A
“PLESIOCHRONOUS” SIGNAL.
 PDH SIGNALS ARE NEITHER
SYNCHRONOUS NOR ASYNCHRONOUS.
 THERE
ARE TWO VERSIONS OF PDH
NAMELY
 1) THE EUROPEAN AND 2 ) THE
AMERICAN.
 THEY DIFER SLIGHTLY IN THE DETAIL
OF THEIR WORKING BUT THE
PRINCIPLES ARE THE SAME.
 EUROPEAN PCM = 30 CHANNELS
 NORTH AMERICAN PCM = 24 CHANNELS
 JAPANESE PCM = 24 CHANNELS
 IN INDIA WE FOLLOW THE EUROPEAN
PCM OF 30 CHANNELS SYSTEM
WORKING
MUX
BIT RATE
2 Mbps
2.048 Mbps +/- 50
30
8 Mbps
ppm
8.448 Mbps +/- 30
ppm
120
34.368
Mbps
140 Mbps 139.264
Mbps
34 Mbps
PARTS
PER
MILLION
CHANNEL
S
+/- 20 ppm
480
+/- 15 ppm
1920
 LOWER
CAPACITY.
 ADD AND DROP DIFFICULT.
 COMPLEX MULTIPLEXING AND
DEMULTIPLEXING.
 NO UNIVERSAL STANDARD
 INTERWORKING BETWEEN
HIERARCHIES COMPLEX
 PDH
IS NO LONGER EFFICIENT TO
MEET THE DEMANDS PLACED ON IT.
 BANDWIDTH LIMITATIONS – MAX
CAPACITY IS 566 MBPS ONLY.
 NO COMMON STANDARDS AMONG
VENDORS
 POINT TO POINT CONFIGURATION (
LINEAR WORKING ) ONLY IS
POSSIBLE.
 IT DOES NOT SUPPORT HUB
 Because
of the disadvantages in the
pdh technology, sdh technology is
developed which overcomes all the
drawbacks of an pdh technology.
 thus
sdh is an advanced technology.
 SYNCHRONOUS :
 ONE MASTER CLOCK & ALL
ELEMENTS SYNCHRONISE WITH IT.
 DIGITAL:
 INFORMATION IN BINARY.
 HIERARCHY:
SET OF BIT RATES IN A HIERARCHIAL
ORDER.

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
SIMPLIFIED MULTIPLEXING/DEMULTIPLEXING
TECHNIQUES.
DIRECT ACCESS TO LOWER ORDER TRIBUTARIES.
ACCOMMODATES EXISTING PDH SIGNALS.
CAPABLE OF TRANSPORTING BROADBAND
SIGNALS.
MULTI-VENDOR, MULTI OPERATOR
ENVIRONMENT.
PROTECTION SWITCHING TO TRAFFIC IS
OFFERED BY RINGS.
ENHANCED BANDWIDTH.
NMS FACILITY.
UNLIMITED BANDWIDTH
GROWTH OF THE EXISTING TO THE HIGHER
ORDER SYSTEM IS SIMPLE.
 LOW/HIGH
SPEED DATA
 VOICE
 INTERCONNECTION
 COMPUTER
OF LAN
LINKS
 FEATURE SERVICES LIKE HDTV
 BROAD BAND ISDN TRANSPORT
SDH Levels
STM-1
STM-4
STM-16
STM-64
Bit rates in Kbps
155520
622080
2488320
96215043.28
 The
different network elements
are
 TERMINAL MULTIPLEXER
 ADD/DROP MULTIPLEXER
 REGENERATOR
 SYNCHRONOUS DIGITAL
CROSS CONNECT
ADM
ADM
(STM1/STM4/STM16)
Aggregate signal
Tributary
(2/34/140Mbps/STM1(e)/ STM1(o))
signal
 Pdh
is obsolete now a days and replaced by
sdh technology
 Sdh has many advantage over pdh technology
 Sdh encompasses features like hdtv ,isdn
services which pdh is incapable of
 It also provides high speed data transfer