Transport Technology Training

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 Agenda Day-1
 Evolution of Transport Networks
 Transport Network overview
 Multiplexing and Modulation techniques
 Wired and wireless Transmission Systems
 Comparison of Microwave Radio and Optical systems
 Network topologies

 PDH, SDH, ATM Technology Overview

 PDH Hierarchy
 Advantages of SDH
 Frame Structure of SDH
 Overhead description of SDH
 Brief Overview of ATM
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 Agenda Day-2
 Optical Fiber Types, Components and Elements
 Principle of optical fiber communication
 Advantages and Disadvantages of OFC
 Types of fiber, applications and components
 Fiber laying methods

 DWDM Networks
 Overview of Multiplexing techniques
 Concept of WDM
 CWDM and DWDM
 Transmission and application mode
 Different types of dispersion in optical fiber

3
 Agenda Day-3
 OTN/ASON concept
 OTN concept
 OTN frame structure and trails
 ASON concept
 ASON protocols and functions

 MPLS-TP
 Basic Concept and OAM of MPLS-TP
 EoSDH concept and different protocols (GFP, VCAT and LCAS)

 Monitor network KPIs of transport network

 Capacity utilization in10G, 40G, 100G DWDM networks
 Availability – equipment , link & network
 Alarm monitoring, Measurements and Performance Reports
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 Agenda Day-4
 Various Network Element, Functions
and configurations
 HW redundancies in NEs
 Network protection schemes
 Ring Protection ( SNCP, MSP, Uni, Bi etc.)
 ASON Vs Ring

 Type of cross connects in multiple protections

 Circuit & Fiber path redundancy
 Inventory building blocks on NEs
 External Alarm & Sync ports

 ILD network for Transoceanic cable

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 Evolution of Transport Networks

6
 Objective
 To know different modulation and multiplexing techniques.

 To describe transport network and its components.

 To familiarized with different medium in transport network.

 To provide overview of Access technology (DSL)

 To describe the microwave communication system

 To compare microwave with fiber medium.

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 Mobile Telecommunication Evolution

Speed (bit/s)

10M
HSDPA High
quality video

3G/ 1M
WCDMA Medium
quality video

384 k
Mobile office
EDGE
Internet Graphics 115 k

GPRS
Internet Text
56 k
Voice
GSM 10 k
Messaging
SMS 1k

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 Telecommunication
• The communication at a distance by technological means through
electrical signals or electromagnetic waves.

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 Transport Network
• Inter-connection of different telecom nodes for data transmission.

• Components of Transport Network

– Telecommunication services
– Data carrying capacity
– Transmission distance
– Transmission medium
– Tx/Rx Frequency
– Transmission network topology
– Network Management System
– Modulation/Demodulation techniques
– Technological node
 Multiplexing/Demultiplexing techniques

10
 Multiplexing
• Combining of multiple streams of information for transmission over a
single medium.

• Splitting a combined stream arriving from a single medium into the

original multiple streams.

• Types of Multiplexing
– FDM
– TDM
– WDM

11
 Modulation
• Some parameter of the carrier signal is made proportional to the
instantaneous amplitude of the information signal.

• Analog Modulation
– AM, FM and PM
Modulating Modulated
Modulator
signal signal
• Digital Modulation
– ASK, FSK and PSK

• Optical Modulation Carrier

– LIM

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 Digital Modulation
• Base Band signal is digital.

BPSK, QPSK, QAM

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 Digital Phase Modulation: PSK
• BPSK
Q

1 0

Q
10 11 A

• QPSK I

00 01
11 10 00 01

• QAM
– Phase and Amplitude Modulation

14
 Optical Modulation: Light Intensity Modulation
• Optical power output of a source is varied in accordance with amplitude of
modulating signal.

15
 Transmission Methods for Telecommunication
• Methods used to carry different information

Coaxial Cable

Fiber

MUX MUX
Radio Microwave Radio
Ter. Ter.

Satellite

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 Transmission Medium
• Transmission Medium is the mean through which signal is transferred
from one place to another.

• Wired or Guided or Medium

– Twisted pairs cable
– Coaxial cable
– Waveguide
– Fiber optics cable

• Wireless or Unguided Medium

– Ground propagation
– Sky propagation
– Line-of-sight propagation
 Microwave Communication

17
 Network Topologies
• The geometric shape used to describe the physical interconnection of the
various telecommunication nodes for flowing of data.

– Point-to-point

– Bus

– Star

– Ring

– Mesh

– Tree

– Hybrid

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 Telecommunication Network Layers
• Access Network Layer

• Distribution Network Layer

• Core/Backbone Network Layer

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 Telecommunication Services
• Fixed Telecom Network
– Landline phone connection (PSTN)
– Data (LAN/WAN)
– Digital Subscriber Loop (DSL)
 Voice
 Internet

• Mobile Telecom Network

– Cordless phone
– Walky-talky or WLL
– Cellular phone network
 2G/3G/4G

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 Copper Cable Fixed Access Network: DSL
• Digital Subscriber Line is one of the main technology used to provide
Broadband services over a existing copper phone lines called local loop.

Telephone exchange

User end

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 Features of DSL Technology
• DSL uses existing twisted-pair copper telephone line.

• Voice is transferred on lower and data on higher frequency bands using

QAM modulation.

• Modem installed at user end and

service provider end (CO).

• At CO, DSLAM terminates and aggregates incoming DSL lines and

redirects the voice traffic to PSTN.

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 Different Types of DSL Technologies: XDSL
• Disadvantages of XDSL
– Name
More powerMeaning
loss Data Rate Connection Distance Applications
Type to
– Cross Talk exchange
– Less distance
DSL Digital subscriber 160 Kbps Symmetrical 5 Kms ISDN, Voice and
– Less bandwidth
line Data Commn.

HDSL High Data Rate 2 Mbps Symmetrical 4 to 5 Kms E1, LAN/WAN

Digital Subscriber
Line

SDSL Symmetric Digital 2 Mbps Symmetrical 3 to 4 Kms Same as HDSL

Subscriber Line +POTS

ADSL Asymmetric Digital Down: 1.5 to 8 Asymmetrical 3 to 6 Kms Video on

• Transport technology next to XDSL
Subscriber Line Mbps
Up: 128 Kbps to 768
demand,
Simplex video,
– PDH Kbps Remote LAN
access,
– SDH Multimedia
– ATM
VDSL
– DWDMVery High Data
Rate Digital
Down: 13 to 52
Mbps
Asymmetrical 0.3 to 1.5
Kms
Same as ADSL +
HDTV
– OTN Subscriber Line Up: 1.5 to 2.3 Mbps

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 Microwave Communication System Components
• Used as backhaul in mobile communication between BTS and BSC.

MW Antenna
• IDU: It is a digital Modem which convert PDH/SDH
signal into IF signal and vice-versa.
IF cable

• ODU: Convert IF signal into RF ODU

(Microwave) signal and vice versa. Pole
IDU

• IF cable: Used to connect IDU and ODU for signal transverse.

• Passive Parabolic MW Antenna : For Trans and Receive RF Signal.

– Antennas are available in different size: 0.2, 0.3, 0.6, 0.9, 1.2, 1.8, 2.4 and 3 mtr dia.

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 Microwave Frequency Bands
• Low-frequency bands (6G/7G/8G/11G) are suitable for long-distance links.
– Nominal Hop Distances 25 – 40 Km

• High-frequency bands (13G/15G/18G/23G/26G/38G) are suitable for short-

distance links.
– Nominal Hop Distance 1 – 10 Km.

• Govt. Body involved

– SACFA (Standing Advisory Committee for Frequency Allocation)
 It is a government wing which gives tower height clearance.

– WPC (Wireless Planning Committee)

 It is a government wing which allocates Frequency and
takes charges from operator for use of MW frequency pair.

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 Microwave Communication Method
• Line of Sight (LOS)
– The microwave frequency band (2 – 38 GHz) is used for LOS propagation mode.
– Microwave radio system requires LOS

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 Antenna Polarization in Microwave System
• The polarization of an antenna is the orientation of the electric field of the
radio wave with respect to the Earth's surface.

• Vertical polarization
– If the electric field is perpendicular to the ground, the radio wave is defined as vertical
polarized.

Vertical Polarization

• Horizontal polarization
– If this electric field is parallel to the ground, the radio wave is said to be horizontal
polarized.

Horizontal Polarization

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 Antenna Alignment
• Pan the antenna by Multi-meter
Multi-Meter
RSSI or AGC
+3.45V
Voltage
ODU
IF CABLE

RSSI/VAGC

1st Side Lobe Azimuth

Main beam

IDU

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 Example: Calculation of Rx Level

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 Microwave vs Fiber Medium

Microwave (MW) Optical Fiber

Easy to cross the space, few land Optical cable needs large
needed, avoid the private land land.

Low investment, short period, High investment, long

easy to maintain Construction period
Anti-natural disaster, Outside cable maintenance,
can be restored fast natural disaster influence

Need to apply the frequency

No frequency license required
license
Performance affected by weather Performance stable, less
and landform influence from outside

Low transmission capacity High transmission capacity

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 Questionnaires???
• What are the transmission methods of telecommunication?

• What is a transport network?

• What is unguided medium?

• Compare Microwave with Fiber?

• What are types of Digital modulation?

• What are the types of PSK?

• What are the types of multiplexing?

• What types of polarization are used in microwave system?

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 PDH, SDH, ATM Technology

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 Objective
 To get familiarized with transport technology.

 To know about the frame structure of PDH, SDH and ATM.

 To have a comparison between these technologies.

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 Plesiochronous Digital Hierarchy (PDH)
• Allowing some variation on the speed around a nominal rate.

• Having 32 time slots frame.

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 Disadvantages of PDH
• Inability to identify the individual channels in higher order stream.

• There are different hierarchies in use in the world.

• Changing from one hierarchical level to another requires additional

equipment.

• No Compatibility of signals between different global vendors.

• More stuffing bits used, so wastage of Bandwidth.

• Insufficient capacity for network management.

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 Synchronous Digital Hierarchy (SDH)
• Synchronous Digital Hierarchy is a standard for telecommunications
transport formulated by the ITU.

• In SDH Network all Elements are synchronized to a common clock source.

Bit rate Abbreviated SDH SDH Capacity

155.52 Mb/s 155 Mb/s STM-1 63 E1

622.08 Mb/s 622 Mb/s STM-4 4 E4

2488.32 Mb/s 2.4Mb/s STM-16 16 E4

9953.28 Mb/s 10 Mb/s STM-64 64 E4

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 Advantages of SDH
• The SDH is based on global international standard.

• Standard interfaces between equipment.

• Facilities to add or drop tributaries directly from a high speed signal.

• SDH allows existing PDH hierarchies to be transported on it.

• Greater equipment reliability due to protection.

• Advance network management features.

• Single stage multiplexing into the higher bit rates.

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 Characteristics of the SDH network Architecture
• Digital multiplexing

• Fiber optics

• Protection schemes

• Ring topologies

• Network administration

• Synchronization

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 STM-1(155.52 Mbps) Formation
• Number of rows in a frame :9
• Number of columns in a frame : 10 + 260 = 270
• Number of bytes/frame : 9 x 270
• Number of bits /frame : 9 x 270 x 8
• Number of bits per second : 155.52 Mbps

125 usec.

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 Sub-units of SDH Frame

+POH +TU PTR

2 Mbit/s
C-12 VC-12 TU-12 x7 x3 +AU-4 PTR +SOH
2 Mbit/s
C-12 VC-12 TU-12 TUG-2 TUG-3 VC-4 AU-4 STM-1
2 Mbit/s
C-12 VC-12 TU-12

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 K L M Schemes for SDH Timeslots
• By order scheme
– VC-12 number = (TUG-3 number - 1) x 21 + (TUG-2 number -1) x 3 + TU-12 number.

K M

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 K L M Schemes for SDH Timeslots
• Interleaved scheme
– VC-12 number = TUG-3 number + (TUG-2 number - 1) x 3 + (TU-12 number -1) x 21.

K M

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 140Mbps to STM-1 Formation

Plesiochronous Signal
(139.264 Mbps)

Container
C-4
Path Overhead
(POH)
Virtual Container
C-4 POH
AU-4 Pointer
AU-4 Administrative Unit
VC-4
Section PTR
Overhead
(SOH)
STM-1
AUG (= AU-4) SOH

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 SDH Basic Operation
• Mapping
– Container is provided for each PDH tributary signal.

– Containers are much larger that the payload to be transported. Remaining capacity is
partly used for justification (stuffing).

1.600 Mbit/s

2.176 Mbit/s

6.784 Mbit/s

48.384 Mbit/s

149.760 Mbit/s

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 SDH Basic Operation
• Multiplexing
– Multiple Lower order path layer signals are adapted into a Higher order path.

– In SDH network, all equipments are synchronized to an overall network clock.

STM-1 : 155.52 Mbps

STM-4 : 622.08 Mbps
STM-16 : 2488.32 Mbps
STM-64 : 9953.28 Mbps

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 SDH Basic Operation
• Aligning
– A pointer with each VC is added which indicates the position of the beginning of the VC
with respect to the STM1 frame.

– Due to pointer, multiplexing and demultiplexing possible in a single device across all
levels.

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 Section Overheads (SOH)

1 2 3 4 5 6 7 8 9
1 A1 A1 A1 A2 A2 A2 J0

2 B1 E1 F1 RSOH

3 D1 D2 D3

4 AU-4 Pointer

5 B2 B2 B2 K1 K2

6 D4 D5 D6

7 D7 D8 D9 MSOH

8 D10 D11 D12

9 S1 M1 E2

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 RSOH Bytes

A1..A2 Framing bytes - designate start of STM-1 frame (Synchronization)

B1 RS Bit Interleaved Parity (BIP-8) - parity computed over previous frame
(Error Mon)
J0 RS trace – Regeneration connection verification
E1 RS orderwire – 64 kbit/s voice connection for operators
F1 RS user channel – 64 kbit/s user channel for operators
D1..D3 RS data communications channel (DCC) – 192 kbit/s- used
OAM channel (Operations, Administration and Maintenance) for NMS

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 MSOH Bytes
B2..B2 MS bit interleaved parity (BIP-24) - parity computed over previous
frame (Error Monitoring)
E2 MS orderwire – 64 kbit/s voice connection for operators

D4..D12 MS data communications channel (DCC) – 576 kbit/s

OAM channel (Operations, Administration and Maintenance)
M1 MS remote error indication (REI) – number of errored BIP-24 blocks
received at the remote end
K1/K2 Automatic protection switching (APS) – MS protection /
alarm indication signal (AIS) / remode defect indication (RDI)
S1 Synchronisation status – Quality of STM-1 signal when used as
synchronisation and timing source

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 POH- Path Overhead Bytes
VC-3/4 POH

J1 Path trace – Identification of path, user programeable, 15 characters

B3 Path bit interleaved parity (BIP-8) - parity over previous container (Error Mon)

VC-11/12/2 C2 Path signal label – mapping type in VC-n (sync, async 34 or 140Mb, ATM)
POH
V5 G1 Path status – monitoring of bidirectional path status,RDI and AIS or REI
J2
N2 F2 Path user channel – 64 kbit/s user channel for operators
K4
H4 Tributary unit multiframe position indicator - start of multiframe, LOM
F3 Path user channel – 64 kbit/s user channel for operators
K3 Automatic Protection Switching (APS) – path protection at higher order
N1 Network operator byte – tandem connection maintenance overhead (TCOH)

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 Path, Section and Overheads in SDH Network
• Overheads vs Sections in a SDH network

Lower Order Path

Higher Order Path

Multiplex
Section
Regenerator
Sections VC-2
VC-12 VC-3 VC-4 VC-4 VC-3 VC-12

SMX

SMX
VC-1
Reg VC-1
VC-1
VC-4 VC-4 VC-2
VC-2
VC-3 VC-3 VC-3

STM-n STM-n
RSOH RSOH
STM-n MSOH
VC-4/3 POH
VC-1/2/3 POH

51
 Network Elements in SDH
• Terminal Multiplexer (TM)
– It combines the Plesionchronous and Synchronous input signals into higher bit rate STM-N Signal.

PDH Terminal STM-N

SDH Multiplexer
• Add/Drop Multiplexer (ADM)
– Extraction from & insertion of Plesiochronous and lower bit rate Synchronous signal from/into high speed
SDH bit streams.
– Used in ring structure of network.

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 Network Elements in SDH
• Digital Cross Connect (DXC)
– Switching of various virtual containers up to and including VC–4.

• Regenerator
– It regenerate the clock and amplitude of incoming distorted and attenuated signal.

STM-N STM-N
Regenerator

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 SDH Ring Topologies
• Ring Network

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 Hierarchical Timing Distribution

PRC

PRC = Primary Reference Clock G.811 N x SECs

1st SSU

SSU = Synchronisation Supply Unit G.812

N x SECs

SEC = Synchronous Equipment Clock G.813 K-1’th SSU

N x SECs

K’th SSU

SDH node always synchronises to signal N x SECs

that has highest quality

If two signals have same quality, priority list K <= 10

N <= 20
determines total SECs <= 60

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 Synchronization in Network

Primary Reference Clock

Caesium (Stratum 1) accuracy 5 x 10-12
PRC Rubidium (Stratum 2) accuracy 2 x 10-11

SSU SSU Synchronization Supply Unit

accuracy 1 x 10-9

SEC SEC SEC SDH Equipment Clock

SDH SDH SDH accuracy 4.6 x 10-6
Equip. Equip. Equip.

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 Different Modes of Synchronization
• Tracing Mode
– System is locked to the reference clock of STM-1 or 2 Mbps or External clock.
– Sync. Status Message (SSM) is sent as “ Do not use for Sync. “ to avoid timing loop.

• Hold Over Mode

– When reference clock failed, system is changed to last memory frequency. This is Hold
Over clock. This can work for about 24 hrs.

• Free Running Mode

– When both the above failed, the system is changed to internal equipment clock.
– When sync. reference is restored, re-synchronize to the reference.

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 Synchronization Status Message (SSM)
• SSM is denoted by b1 to b4 bits of S1 Byte

• SSM can be used only in a chain network

• All networks (ring, mesh) can be divided into chains.

“G.811” “G.811” “G.811”

G.811 SEC SEC SEC G.812
DNU DNU DNU

Direction of synchronisation

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 Synchronization Status Message (SSM)
• SSM enables changing direction of synchronization.

• When a connection is broken, the rest of the network receives

synchronization from the other direction.

A failure between two nodes

DNU DNU
G.811 SEC SEC SEC G.812
“G.812” “G.812”

Direction of synchronisation

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 Synchronization Planning
• Master-slave synchronization

• Priority tables

• Use of SSM enables all network

PRC
topologies to be protected

• Timing loops are avoided by synchronization

planning

1st priority

2nd priority

60
 Clock tracing in normal status

Building Integrated Timing Supply

61
 Link break between NE2 and NE3

62
 External BITS of NE1 is failed

63
 Both external BITS are failed
• Hold over mode then free running mode.

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 SDH Alarms
Alarm Type Description
LOS Drop of incoming optical power level causes BER of 10-3 or worse
OOF A1, A2 incorrect for more than 625 us
LOF If OOF persists of 3ms
B1 Error Mismatch of the recovered and computed BIP-8 (RS)

MS-AIS K2 (bits 6,7,8) =111 for 3 or more frames

B2 Error Mismatch of the recovered and computed BIP-24 (MS)
MS-RDI If MS-AIS or excessive errors are detected, K2(bits 6,7,8)=110

MS-REI M1: Binary coded count of incorrect interleavedbit blocks

AU-AIS All "1" in the entire AU including AU pointer

AU-LOP 8 to 10 invalid pointers

HP-UNEQ C2="0" for 5 or more frames
HP-TIM J1: Trace identifier mismatch
HP-SLM C2: Signal label mismatch

HP-LOM H4 values (2 to 10 times) unequal to multiframesequence

B3 Error Mismatch of the recovered and computed BIP-8 (VC-4)

HP-RDI G1 (bit 5)=1, if an invalid signal is received in VC-4/VC-3

HP-REI G1 (bits 1,2,3,4) = binary coded B3 errors

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 Loss of Signals (LOS)
• This alarm is raised when the STM-N level drops below the threshold at
which a BER of 1 in 1000 bits is detected.

• It could be due to cut cable, excessive attenuation of the signal or an

equipment fault

• The LOS state will clear when 2 consecutive framing patterns are
received.

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 Frame Alarms
• OOF
– This situation occurs when 5 consecutive SDH frames are received with invalid framing
patterns(A1 and A2 bytes)

– The maximum time to detect OOF is therefore 625msec.

– The OOF clears when >= 5 consecutive SDH frames are received with valid framing
patterns.

• LOF
– The LOF occurs when the OOF state exists for a 3 msec.

– As the framing bytes are there in Regenerator section overhead(RSOH) this alarm is
sometimes known as RS-LOF

67
 BER Alarm
• MS-REI
– A return message (M1) from Rx to Tx ,when Rx find B2 bit errors
– Rx generate corresponding performance event MS-BBE
– Tx generate corresponding performance event MS-FEBBE
– Tx generate MS-REI alarm

Traffic

Tx Rx

Return M1
Generate
MS-FEBBE Find B2 bit errors
MS-REI Generate MS-BBE

68
 Virtual Circuit Packet Switching
• A route is established before packets are sent, connection oriented.

• Each packet contains connection virtual connection ID, not IP address.

• Packets are forwarded more quickly

– Based on the virtual connection identifier
– The node need not make a routing
decision for each packet.

• Less reliable
– If a node fails, all virtual circuits that pass
through that node fail.

• Example: X.25, Frame Relay, ATM

69
 Synchronous TDM
• Every possible sender has a reserved time slot, whether it needs or not.

• System leaving slots unfilled when a source does not have a data item
ready in time.

• This may lead to underutilization of the transmission channel bandwidth.

• PDH/SDH uses synchronous TDM

70
 Statistical or Asynchronous TDM
• If a sender’s data is not ready, skip that sender and move to the next.

• All slots will be filled as long as some sender has data ready to send.

• Each slot must also contains an identifier to indicate who is the receiver.

• Take less time to send the data.

• ATM uses Statistical TDM

71
 Asynchronous Transfer Mode (ATM)
• ATM is a circuit-switched, cell-switched data communications method.

• It uses Asynchronous TDM.

• Voice, video, or data, is conveyed in small, fixed-size cells.

• ATM technology is connection-oriented, using virtual logical connection.

• Transmission rate may be from 25.6 Mbps to 1.2 Gbps.

• ATM is L2 technology.

• Switching is carried out by VPI and VCI.

72
 Virtual Connection in ATM
• Virtual Path (VP)

• Virtual Channel (VC)

VC VP VP VC

VC VP
VP Transmission path VP VC

VC VPVP VP VC

VP . . . Virtual Path Uni-directional

VC . . . Virtual Channel

73
 VP and VC Switching

VC switch

VC Level
Endpoint VCI
of VPC 21 VCI VCI VCI
22 23 24

VPI1 VPI3 VPI2

VCI
VCI 21 VPI1 VPI2 24
VCI 22

VCI VP Level
VPI3
23

VCI 21 VCI 21
VPI4 VPI5
VCI 22 VCI 22

VP switch

74
 ATM System Architecture and Protocols

Convert to
Video Cell correct
Electrical
Conversion
or Optical
to ATM
Add 5-Byte Format
Data Types,
Header
48-Byte Length
Data Cell Forward Cell
through Video Data Voice
Network Cell Cell Cell

Voice

Higher Adaptation ATM Physical

Layer Layer Layer Layer

75
 Advantages of ATM over IP
• Small and fixed-size cells
– Information for multiple service types, such as voice, video, or data, is conveyed in
small, fixed-size cells so easy processing.

• Fast forwarding
– Small and fixed size cell of 53 bytes (5 bytes as header and 48 bytes as payload) allows
small buffer and fast data forwarding.
– Not looking up big routing table at each node.

• Real time communication possible

– Connection orientation, no delay variation so real time communication.

• Efficient bandwidth utilization

– ATM uses asynchronous (or statistical) multiplexing.

• QoS
– ATM cells takes same path so QoS possible.

76
 Questionnaires???
• What are the different types of PDH hierarchy globally?
• How a E1 (2Mbps) is formed?
• State two disadvantages of PDH.
• Why SDH network is called synchronized network ?
• State two advantages of SDH.
• What is the function of DXC in SDH network?
• How a STM-1 is formed as 155.52Mbps?
• What are the parts of SDH frame structure?
• What types of TDM technique is used in ATM?
• In ATM, switching is carried out by ______ and ______
• What is frame size of ATM?

77
78
 Optical Fibers, Components and Elements

79
 Objective
 To know the components of fiber

 To describe the principle of optical fiber communication

 To indicate the wavelength windows

 Explain the types of fiber

 Describe the advantages, disadvantages and applications of fiber

80
 Construction of Fiber
• An optical fiber consists of a core, cladding and buffer (a protective outer
coating).

• In the glass fiber core and cladding are made of high quality silica glass.

• The cladding guides the light along the core by using the method of total
internal reflection.

Single Fiber Fiber Cable

81
 Principle of Optical Communication
• Total Internal Reflection
– For all angles of incidence greater than the critical angle, the incident ray will get
reflected back into the denser medium itself. This phenomenon is called total internal
reflection.

82
 Wavelengths in Optical Fiber
• For fiber optics with glass fibers, we use light wavelengths around 850,
1310 and 1550 nm.

• These wavelengths are falling in the infrared region and having less
attenuation.

850 1310 1550

83
 Optical Fiber Communication
• Transmitting information from one place to another by sending pulses of
light through an optical fiber.

• Modulation used: Light Intensity Modulation

84
 Typical Optical System

Between trans and receive ends, Optical Amplifier and Regenerator may be used

85
 Optical Transmitter: LED
• Spectral width of 30-60 nm.

• Communications LEDs are most commonly made from gallium arsenide

phosphide (GaAsP) at 1300 nm or gallium arsenide (GaAs) at 850 nm.

• LEDs are suitable primarily for local-area-network applications with bit

rates of 10-100 Mbit/s and transmission distances of a few meters.

86
 Optical Transmitter: LASER
• LASER diode Produce coherent light.

• High Output power

• The narrow spectral width allows for high bit rates and long distance.

• Better coupling efficiency.

87
 Optical Receiver
• Optical Receiver is made of Photo detector (Photo diode) which convert
light into electrical signal.

• Photo diodes used: P-I-N Photodiodes, Avalanche Photodiodes (APD).

• P-I-N Photodiodes has upto 1300 nm operating wavelength.

• Avalanche Photodiodes has up to 1550 nm operating wavelength.

• APD has more sensitivity than P-I-N Photodiodes.

88
 Optical Transceiver Module
• Fiber optic transceivers include both a transmitter and a receiver in the
same component.

• Transmitter and Receiver are arranged in parallel so that they can operate
independently of each other.

• Used for both single mode and multimode cables.

• Example of transceiver.

SFP

89
 Fiber Connectivity
• A failure any where along this link will cause the entire link to fail.

Transceiver Fiber Optic Cable

Transceiver

Electrical
Connector Electrical
Optical Optical Optical Connector
Optical
Port Connector Connector Port

90
 Classification of Optical Fibers

Optical Fiber

Mode Material Ref. Index

Single Mode Multi Mode Step Index Graded Index

Glass Plastic

91
 Type of Fiber as per Modes

Laser

92
 Multimode Fiber
• Multimode fibers allow a large number of modes.

• A multimode optical fiber has larger core (50 to 100um). Most common
size is 50um or 62.5um.

• LED is used as a light source in multimode fibers.

• Used for low capacity and short distance i.e. LAN

n2 Cladding

n1 Core

93
 Single Mode Fiber
• In a single mode fiber only one mode can propagate through the fiber.

• Core of SM fiber is smaller (8.3 to 10 microns). Common size is 9um.

• Laser is used as light source for single mode fiber.

• Used in long distance communication upto100 Gbit/s data in DWDM.

n2 Cladding

n1 Core

94
 Step Index Optical Fiber
• In the step index fiber, the refractive index of the core is uniform
throughout.

• Different light modes in a step-index multimode fiber follow different

lengths along the fiber in zigzag way.

• The arrival of different modes of the light at different times causes inter
modal dispersion.

input output

95
 Graded Index Optical Fiber
• Graded-index fiber’s refractive index decreases gradually away from its
center.

• Light rays follow sinusoidal paths.

• Reduces inter modal dispersion.

96
 Practically used Optical Fibers
• MM Step index: 62.5/125 μm
• MM Graded index: 50/125 μm
• SM Step index: 9/125 μm
• Single mode graded index is not practically used.

Input Output
Pulse Multimode Single mode
Multimode Step index Pulse

Multimode Graded index

Single mode Step index

97
 Optical Fiber Connectors

LC ST

FC SC

FDDI
MTRJ

98
 OFC Laying Methods

Direct buried

Duct

Aerial
Under water

99
 Advantages of Optical Fibers
• Very high information carrying capacity

• Less attenuation (order of 0.2 db/km)

• Small in diameter and size & light weight

• Greater safety and immune to EMI & RFI, moisture & corrosion

• It is dielectric in nature so can be laid in electrically sensitive surroundings

• Difficult to tap fibers, so secure

• No cross talk and disturbances

100
 Disadvantages of Optical Fibers
• The terminating equipment is still costly as compared to copper
equipment.

• It is delicate so has to be handled carefully.

• High Cost.

• Last mile is still not totally fiberised due to costly subscriber premises
equipment.

• Optical fiber splicing is a specialized technique and needs expertly trained

manpower.

• The splicing and testing equipments are very expensive as compared to

copper equipments.

101
 Applications of Optical Fiber
• Long distance communication: Backbones

• Broadband services

• Computer data communication (LAN, WAN etc..)

• Medical Industry

• Military application

• Non-communication applications (sensors etc…)

102
 Some Manufactures of Optical Fiber
• Furukawa
• Fujikura
• LG Cables
• Corning
• Philips-Fitel
• Pirelli
• TTL
• Sterlite Cables

103
 Questionnaires
• What is the principle of fiber communication?

• What is the condition for Total Internal Reflection?

• What is the Relation of Refractive Index between Core and Cladding?

• What are the optical wavelength windows for communication?

• What is the fiber construction?

• What the fiber colour says?

104
 DWDM Networks

105
 Objective
 To describe the concept of WDM.

 To differentiate the types of wavelengths.

 To know the advantages of DWDM.

 To explain the transmission mode can be used in DWDM network.

106
 Methods for expanding Network Capacity
• Space Division Multiplexing (SDM)

• Time Division Multiplexing (TDM)

• Wavelength division multiplexing (WDM)

 WDM

 Economical &
Mature & Quick
 TDM
 Keeps same Fiber,
 SDM  STM-16→ STM-
same bit rates
64
 Add fiber &
equipment  Cost
&Complication
 Time & cost

Solution of capacity expansion

107
 Why WDM ?
• Number of fiber reduced

• Number of Regenerator or Amplifier reduced

• Capable of graceful capacity growth

• No modification of overhead

Non DWDM Transmission

DWDM Transmission
108
 Concept of WDM？

Patrol Station

Free Way

Patrolling Car

109
 WDM System
• Multiple services onto a single wavelength.

• Multiple wavelength onto a single fiber.

110
 Available Wavelengths in DWDM
• 80 Channels in C-band
– C-Even
 192.10 THz to 196.00 THz (1529.55 nm to 1560.61 nm)
– C-Odd
 192.15 THz to 196.05 THz (1529.16 nm to 1560.20 nm)

ITU-T G.694.1
Extended C band 192chs, 25GHz spacing
Extended
C band 160chs 32chs
196.05THz 192.10THz 192.05THz 191.275THz

• 80 Channels in L-band
– L-Even
 186.95 THz to 190.85 THz (1570.82 nm to 1603.57 nm)
– L-Odd
 187.00 THz to 190.90 THz (1570.42 nm to 1603.17 nm)

111
 Application modes of DWDM
• Open System

MUX DMUX

M
O 4 O
T 0 0
T
4
U U
M

112
 Application modes of DWDM
• Integrated System

MUX DMUX

M
4
0 0
4
M

Client

113
 Transmission Modes of DWDM
• Single Fiber Uni directional transmission
– Wavelengths for one direction travel within one fiber l1
l3 l2
l5 l4
l6 Fiber
l7 l8

– Two fibers needed for Full-duplex system l2

l1
l3
l4 l5
l6 Fiber
l7
l8

Uni -directional

M
O 4 O
0
T 0 T
4
U U
M

MUX DMUX

114
 Transmission Modes of DWDM
• Single Fiber bi-directional transmission
Fiber
– A group of wavelengths for each direction l5
l6 l1
l7 l2
l8 l3
l4

– Single fiber operation for full-duplex system

Bi -directional

M
O 4 O
0
T 0 T
4
U U
M

MUX/DMUX DMUX/MUX

115
 Coarse Wavelength Division Multiplexing (CWDM)
• CWDM typically uses 20-nm spacing (3000 GHz) of up to 18 channels.

• Target distances up to about 50 km on single mode fibers

• Within the range 1270 nm to 1610 nm. Used in metro city i.e CATV.

116
 Dense Wavelength Division Multiplexing (DWDM)
• DWDM spaces the wavelengths more closely, may be 100, 50, or 25 GHz
(0.2nm to 0.8nm, within C-band 1530-1565nm)

• With a channel count reaching up to 192, distances of several thousand

kilometers.

Single Fiber

117
 Optical Network Hierarchy

80  10G 80  40G
DWDM
NMS (NOC) Backbone layer

DCN

STM-16 40  10G STM-64

DWDM
Convergence layer

STM-4
STM-16 STM-4STM-4/1
STM-1
SDH/DWDM
Access layer

118
 Optical Transport Network
• Connecting number of optical nodes with fiber cables for data transferring.

• Faster and high capacity as compared to other type of Network.

• Optical network can be used to supply internet, television, telephone and

data access.

• DWDM Network is an example of

Optical Transport Network.

Fiber

119
 DWDM Components

l1
850/1310/1550 15xx l1...n
l2

l3
Transponder
Optical Multiplexer

l1
l1
l2 l1...n
l2
l3
l3

Optical De-multiplexer

Optical Add/Drop Multiplexer

(OADM)

120
 DWDM Components

Optical Amplifier Optical Attenuator

(EDFA) Variable Optical Attenuator

Dispersion Compensator (DCM / DCU)

121
 DWDM System Block Diagram

OSC

Mux
Client ODD

Transponder ITL OA
Signal (DWDM)
FIU

Mux
EVEN

(DWDM)
ROADM
Optical D A
Fiber
DeMux
OA ITL ODD
FIU Client
Transponder
(DWDM) Signal

DeMux
OSC
EVEN

(DWDM)

122
 Basic Power Level Concept

Units Calculation

 mW P(mW)
 P (dBm)=10log
The unit of optical power 1(mW)

 dBm
 0dBm = 1 mW
The unit of optical power
 10dBm= 10 mW
 dB
The unit of gain or attenuation  20dBm = mW
of optical power  20dBm-10 =10dBm

123
 Optical Power Calculation

P1
Ptotal

P2

Ptotal (mW) ＝ P1 (mW) + P2 (mW)

Ptotal (dBm) ＝Psingle (dBm) +10lg2(dB)

The situation of N wavelengths

Ptotal (dBm) ＝Psingle (dBm) +10lgN(dB)

124
 Fiber Optic Loss Budget
• Basic elements to determine estimate total link loss.
– Fiber Loss Factor

– Type of fiber

– Transmitter
Pout = +6 dBm Budget = 36 dB Senstivity = -30
dBm
– Receiver Sensitivity

– Number of splices

– Types of splices

– Margin

125
 Fiber Optic Loss Budget Calculation

Fiber Loss: 14.5 km × 0.35dB = 5.075 dBm

Fusion splice Loss: 0.2dB
Terminating Connectors Loss: 5 × 1.0dB = 5dB
Margin: 5dB
Total Budget Loss: 5.075+0.2+5+5= 15.275dB

Transmit Power: -3dBm

Rx Level: -3-15.275= -18.275 dBm

Receiver Sensitivity: -20dBm

1dB 0.2dB

Margin= 5dB
-3dBm

14.5km @ 0.35dB/km

126
 Characteristics: Optical Transmitter and Receiver
• Mean Launch Power

• Receiver sensitivity: A

• Receiver overload: B

• Recommended Receiving Power Range: A+3(dBm) ~ B-5(dBm)

127
 DWDM Test Parameters
• Power levels of the individual wavelength
– To ensure flat power distribution over the entire bandwidth to notice immediately
whether any channels have added/dropped.

• Channel wavelength / Channel spacing

– To indicate possible wavelength shifts for individual laser sources.

• Optical Signal to Noise Ratio (OSNR)

– To ensure that error-free transmission is possible in each data channel.

• Overall power
– To check the optical fiber amplifiers of the system to check against safety limit.

128
 Optical Power Meter (OPM)
• OPM measure the average optical power out of an optical fiber.

• Power meters are calibrated at the typical wavelengths used in fiber

optics, 850, 1300 and 1550 nm.

• Some meter uses Auto wavelengths Recognition

feature.

129
 Optical Light Source (OLS)
• OLS along with Optical Power Meter is used to make measurements of
optical loss or attenuation in fibers, cables and connectors.

• It should be compatibility with the type of fiber in use (singlemode or

multimode with the proper core diameter) and the wavelength.

• Sources may be either LED's or LASERS.

• Sometimes optical power meters are combined with an Optical Light

Source (OLS) or Visual Fault Locator (VFL).

130
 OTDR
• Optical Time Domain Reflectometer (OTDR) is used for estimating the
fiber’s length and overall attenuation, including splice and mated-
connector losses and to locate faults, such as breaks.

• OTDR functions by injecting a series of optical pulses into the fiber under
test, using LASER or LED.

• It requires access to only one end of the fiber.

131
 Fiber Trace at OTDR
Near End
Reflection And
Dead Zone

A B

Reflective Event End Of

B/Scatter Fiber
(Mech. Splice Or
Connector)

dB
Fresnel Refl.
None Reflective
Event (Fusion
Splice Or Bend)

Distance

132
 Optical Spectrum Analyzer (OSA)
• Optical signal monitoring on live channels.

• Monitor access port required.

• Able to analyze
– Optical Power

– Optical wavelength

– OSNR of each wavelength

– Spectral width of optical source

133
 DWDM Network Planning Points
• Determining the spectral width and spacing of wavelengths

• Wavelength Stabilization

• Types of fiber

• Span loss (fiber+connector+splicing loss)

• Optical Amplifier or Regenerator

• Control of dispersion

134
 Signal Degradation in Optical Fiber
• Attenuation and dispersion determine the quality of optical signal intern
the maximum distance an optical signal can be transmitted.

• The attenuation and dispersion of a fiber are wavelength dependant.

135
 Transmission Losses in Fibers
• Transmission loss or attenuation of the signal in an optical fiber is
measured in dB/km.
– 0.40 dB/km at 1310 nm
– 0.25 dB/km at 1550 nm

1550
Window
1310
Window

136
 Dispersion overview
• Broadening of pulse causes ISI.

• It is measured in ps/nm.km

137
 Types of Dispersion
• Intermodal dispersion

• Material dispersion

• Waveguide dispersion

• Polarization mode dispersion

138
 Intermodal Dispersion
• Each mode enters the fiber at a different angle, take different path, travel
different distance and arrive at different time at the fiber output.

• Multimode fibers have many different light modes since they have much
larger core size.

• The light pulse spreads out in time which can cause signal overlapping.

139
 Material Dispersion
• Dependence of refractive index of the material on wavelengths.

• The velocity of light through a fiber depends on its wavelengths.

• Different wavelengths travel at different velocity due to refractive index,

hence the different propagation causes material dispersion.

• Material dispersion at 1300nm for silica is zero.

140
 Waveguide Dispersion
• Distribution of light between core and cladding is a function of the
wavelength travelling in waveguide.

• Light ray that travels in the cladding travels faster than that in the core
causes waveguide dispersion.

• Single mode fiber suffers from waveguide dispersion as it has small core
diameter.

141
 Chromatic Dispersion
• Combined effect of Material and Waveguide Dispersion

142
 Polarization Mode Dispersion (PMD)
• Mechanical and thermal stresses during fiber manufacturing introduces
small index of refraction differences for the two polarization states.

• Polarization Mode Dispersion (PMD) a form of modal dispersion, causes

broadening of the input pulse due to a phase delay between input
polarization states.

143
 Effect of Dispersion
• Spreading of pulses which can cause Inter Symbol Interference (ISI).

• Detection of individual pulse is not easy at receiver.

• Poor BER performance.

• Limit the communication distance.

• Limit the transmission rate.

144
 Dispersion Compensating Module (DCM)
• By joining fibers with CD of negative dispersion and suitable lengths an
average dispersion close to zero can be obtained.

145
 SM Fiber Applications with Dispersion Feature
• G.652-Non-Dispersion-Shifted Fiber (SMF-28)
– Chromatic dispersion would be close to zero (lambda zero) near the 1310nm
wavelength.
 Good for TDM at 1310nm
 Bad for TDM at 1550nm
 OK for WDM at 1550nm

• G.653-Dispersion Shifted Fiber (DSF)

– Designed for lower attenuation with zero-dispersion (lambda zero) point at 1550nm.
 Good for TDM at 1550nm
 Bad for WDM at 1550nm

• G-655-Non-Zero Dispersion Shifted Fiber (NZ-DSF)

– For NZ-DSF, Dispersion is low in the 1550nm region but not zero.
 Good for TDM and DWDM at 1550nm

146
 Degradation Parameters in Fiber
• A Light Pulse Propagating in a Fiber Experiences 3 Type of degradations.

Pulse as It Enters the Fiber Pulse as It Exits the Fiber

Loss of Energy

Shape Distortion

Phase Variation

Loss of Timing (Jitter)

(From Various Sources) t t
ts Optimum ts Optimum
Sampling Time Sampling Time

147
 Optical Regenerator
• Regenerate an optical signal by converting optical signal to an electrical
signal, processing that electrical signal and then retransmitting an optical
signal.

• Overcoming loss due to attenuation of the optical fiber and distortion of

the optical signal.

• Also known as 'optical-electrical-optical' (OEO).

148
 Classification of Regenerators
• 1R : Reamplification of the data pulse alone is carried out.

• 2R : In addition to Reamplification, pulse Reshaping is carried out.

• 3R : In addition to Reamplification and Reshaping, Retiming of data pulse

is done.

149
 Optical Amplifier
• Disadvantage of OEO (Regenerator)
– OEO repeaters are expensive and difficult to manufacture.

– One repeater (OEO) is required for each wavelength, so a lot of equipment is required
for each fiber.

• Optical amplifiers boost optical signals to minimize the effects of power

loss and attenuation.

• EDFA is the most commonly used Optical Amplifier.

150
 Application of EDFA
• Booster Amplifier

• Line Amplifier

• Pre Amplifier

OTU D
OTU
M M M M
4
U OA OA4 OA4 4M
U
0
X 0 0 0X
OTU OTU

Booster amplifier Line Amplifier Pre-amplifier

151
 Limitations of Erbium Doped Fiber Amplifier
• Each amplifier adds noise.

• OSNR decreases gradually along the chain.

• Gain flatness is another key parameter mainly for long amplifier chains.

• We can have only a finite number of amplifiers and spans and eventually
Optical Regenerator will be needed.

152
 Questionnaires
• Explain the methods for expanding network capacity?

• What is the purpose of OSC channel?

• What is the wavelength of OSC channel?

• What is the purpose of transponder card in DWDM equipment?

• What is unidirectional and bidirectional fiber?

• What is difference between CWDM and DWDM?

153
154