Upload
jatin-phore
View
167
Download
2
Embed Size (px)
Citation preview
Page | 1
INDUSTRIAL TRAINING REPORT
ON
SDH Technology & Optical Fiber Communication System
SUBMITTED TO: SUBMITTED BY:
Mr.Ujjwal Shukla Jatin
(Company Mentor) 2K13/EC/069
Senior Manager(NOC) Btech DTU
RailTel Corporation of India Ltd. Semester: V
Year: 2015-16
Page | 2
TABLE OF CONTENTS
Sr No. Particular Page No.
1. Abstract 3
2. Introduction 4
3.
3.1.
3.2.
3.3.
About The Organisation
Company’s objectives
Major Clients of RailTel
Services Provided by RailTel
5
5
5
5
4.
4.1.
4.2.
Optical Fibre
Fibre Cable Types
Fibre Geometry Parameters
10
11
12
5.
5.1.
5.2.
Fibre-Optic Communication
Key Components for Optical Fibre Communication
Types of Transmission (Short v/s Long Haul)
13
13
14
6.
6.1.
6.2.
6.3.
6.4.
6.5.
Multiplexing
Types of Multiplexing
Time Division Multiplexing
SDH Frame
SONET/SDH Data Rates
SDH Network in RailTel
15
15
16
19
21
22
7. References 23
Page | 3
1. ABSTRACT
The project mainly aims at making us aware of how a signal in optical communication
actually travels & how total communication network is established; which means we
get to know the responsibilities, constraints & freedom under which an engineer works
& how telecommunication happens.
We also get an opportunity to analyse the life cycle working of an organisational
hierarchy from setting up the network to sending the signal & receiving it with
minimum attenuation.
The complete MPLS network is managed by centralized network management system
(NMS) located at New Delhi with back up at Secunderabad. For the SDH/DWDM
network RailTel has NOC (Network Operating Centre) situated at all regional HQs
which maintains the network under their respective territory. However, each of the
NOC is provided with back up on the other regional NOCs. RailTel has got the unique
advantage to meet the quality bandwidth and service requirements from single network.
The state of art network enables point and click provisioning of the bandwidth from
anywhere to anywhere in the country. It enables provisioning of traffic of any
granularity with the extensive reach from any part of the country to any other part.
PDH (Plesiochronous Digital Hierarchy) & SDH (Synchronous Digital Hierarchy)
work on Time Division Multiplexing (TDM) technology. PDH isn’t synchronized &
each system has its own clock whereas SDH is fully synchronised. Also multiplexing
& de-multiplexing is required at each level in PDH but not in SDH. SDH can transfer
bytes at more flexible & higher rates than PDH.
The SDH uses a digit rate of 155.52 Mb/s and multiples of this by factors of 4n, e.g.
622.08 Mb/s and 2488.32 Mb/s. Any of the existing CCITT plesiochronous rates can
be multiplexed into the SDH common transport rate of 155.52 Mb/s. The SDH also
includes management channels, which have a standard for network-management
messages. The basic SDH signal, called the synchronous transport module at level 1
(STM-1).
Ethernet is the most widely installed local area network (LAN) technology. Ethernet is
a link layer protocol in the TCP/IP stack, describing how networked devices can format
data for transmission to other network devices on the same network segment, and how
to put that data out on the network connection. It touches both Layer 1 (the physical
layer) and Layer 2 (the data link layer) on the OSI network protocol model. Ethernet
defines two units of transmission, packet and frame.
The most common forms used are 10BASE-T, 100BASE-TX, and 1000BASE-T.
Page | 4
2. INTRODUCTION
As has been previously discussed in the Project Proposal, the tentative schedule of the
project is as follows:
Week Process
Week 1 To understand the working and objectives of organisation
Week 2 To study the major highlights of Optical Fibre Communication system
Week 3 Understanding multiplexing techniques basics for PDH & SDH
Week 4 Understanding SDH and STM frames
Week 5 To study SDH Network topologies & Protection schemes
Week 6 To study the communication through Ethernet.
Week 7 To study DWDM
Week 8 Working on Network Management System (NMS)
Week 9 Project Review & submission of Final Report
Page | 5
3. ABOUT THE ORGANIZAION
RailTel Corporation of India Limited (RailTel) is a Government of India undertaking
under the Ministry of Railways.
The Corporation was formed in Sept 2000 with the objectives to create nation-wide
Broadband Telecom and Multimedia Network in all parts of the country, to modernize
Train Control Operation and Safety System of Indian Railways and to significantly
contribute to realization of goals and objective of national telecom policy 1999.
RailTel is a wholly owned subsidiary of Indian Railways, with authorized capital of
Rs.1000/- Crores.
RailTel has created state of the art multimedia telecom network using SDH/DWDM
based transmission systems and high end routers for MPLS-IP network
3.1 Company’s Objectives:
To expeditiously modernise Railways' train control, operational and safety systems and
networks.
To create a nationwide broadband telecom and multimedia network to supplement
national telecom infrastructure to spur growth of telecom Internet and IT enabled value
added services in all parts of the country specially rural, remote and backward areas.
To significantly contribute to realisation of goals and objectives of National Telecom
Policy, 1999 and
To generate much needed revenues for implementing Railways’ development projects,
safety enhancement and asset replacement programmes
3.2 Major Clients of RailTel:
Indian Railways
CRIS
Reliance
Tata Indicom
Hutch
Airtel Sify
Tulip
Tejas
Alcatel
Fibcom
WRI
UTSTAR
3.3 Services Provided by RailTel:
BANDWIDTH SERVICES (From 64 Kbps to 155 Mbps)
RailTel has a vast OFC network capable of providing bandwidth services at a large
number of towns and cities across the country.
INTERNET SERVICES
Page | 6
RailTel is also offering Internet services as an ISP (Internet Service Provider). It has an
ISP category-A license to extend these services. This service is available all along the
OFC network of RailTel.
CO-LOCATIONAL FACILITIES
List of Existing Towers
Northern Region 257
Eastern Region 434
Western Region 162
Southern Region 156
Total Towers 1009
VIRTUAL PRIVATE NETWORK (VPN)
Page | 7
RailTel IP-MPLS Backbone Network Diagram
The complete MPLS network is managed by centralized network management system (NMS)
located at New Delhi with back up at Secunderabad. For the SDH/DWDM network RailTel
has NOC situated at all regional HQs which maintains the network under their respective
territory. However, each of the NOC is provided with back up on the other regional NOCs.
Page | 8
Screenshots of NMS by Alcatel
Page | 9
RailTel NOC (Network Operating Centre) Working
Page | 10
4. OPTICAL FIBRE
RailTel has more than 42,000 Route Km of Optical Fiber Cable running along Indian Railway
Track in many part of the country. RailTel is having fibres at every station enroute, spaced at
8-10 Kms to meet Railway operations. RailTel is laying fibres in uncovered sections & shall
complete 54,000Km of Rail route & covering most of the stations & commercial requirement
(5000+) on its backbone.
Page | 11
An optical fiber (or optical fibre) is a flexible, transparent fibre made by drawing glass (silica)
or plastic to a diameter slightly thicker than that of a human hair. Optical fibres are used most
often as a means to transmit light between the two ends of the fibre and find wide usage in fibre-
optic communications, where they permit transmission over longer distances and at
higher bandwidths (data rates) than wire cables. Fibres are used instead of metal wires because
signals travel along them with lesser amounts of loss; in addition, fibres are also immune
to electromagnetic interference, a problem which metal wires suffer from excessively.
Optical fibres typically include a transparent core surrounded by a
transparent cladding material with a lower index of refraction. Light is kept in the core by the
phenomenon of total internal reflection which causes the fibre to act as a waveguide.
4.1 Fiber cable types:
Fibers that support many propagation paths or transverse modes are called multi-mode
fibers (MMF), while those that support a single mode are called single-mode fibers (SMF).
Page | 12
4.2 Fiber Geometry Parameters:
The three fiber geometry parameters that have the greatest impact on splicing performance
include the following:
cladding diameter: the outside diameter of the cladding glass region
core/clad concentricity (or core-to-cladding offset): how well the core is centred in
the cladding glass region
fiber curl: the amount of curvature over a fixed length of fiber
These parameters are determined and controlled during the fiber-manufacturing process. As
fiber is cut and spliced according to system needs, it is important to be able to count on
consistent geometry along the entire length of the fiber and between fibers and not to rely solely
on measurements made.
–Splicers and Connectors
As optical fiber moves closer to the customer, where cable lengths are shorter and cables have
higher fiber counts, the need for joining fibers becomes greater. Splicing and connectorizing
play a critical role both in the cost of installation an in system performance. The object of
splicing and connectorizing is to precisely match the core of one optical fiber with the help of
which light signals can continue with ways that fibers are joined:
splices, which form permanent connections between fibers in the system
connectors, which provide remateable connections, typically at termination points.
–Fusion Splicing
Fusion splicing provides a fast, reliable, low-loss, fiber-to-fiber connection by heating a
homogenous joint c between the two fiber ends. The fibers are melted or fused together by
heating the fiber ends, typically using an electric arc. Fusion splices provide a high-quality joint
with the lowest loss (in the range of 0.01 dB to .10 dB for single-mode fibers) and are
practically non-reflective.
–Mechanical Splicing
Mechanical splicing is an alternative method of making a permanent connection between
fibers. In the past, the disadvantages of mechanical splicing have been slightly higher losses,
less-reliable performance, and a cost associated with each splice. However, advances in the
technology have significantly improved performance. System operators typically use
mechanical splicing for emergency restoration because it is fast, inexpensive, and easy.
(Mechanical splice losses typically range from 0.05.0.2 dB for single-mode fiber.)
–Connectors
Connectors are used in applications where flexibility is required in routing an optical signal
from lasers to receivers, wherever reconfiguration is necessary, and in terminating cables.
These remateable connections simplify system reconfigurations to meet changing customer
requirements.
Page | 13
5. FIBRE-OPTIC COMMUNICATION
Fiber-optic communication is a method of transmitting information from one place to another
by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier
wave that is modulated to carry information. First developed in the 1970s, fiber-optic
communication systems have revolutionized the telecommunications industry and have played
a major role in the advent of the Information Age. Because of its advantages over electrical
transmission, optical fibers have largely replaced copper wire communications in core
networks in the developed world. Optical fiber is used by many telecommunications companies
to transmit telephone signals, Internet communication, and cable television signals.
The process of communicating using fiber-optics involves the following basic steps: Creating
the optical signal involving the use of a transmitter, relaying the signal along the fiber, ensuring
that the signal does not become too distorted or weak, receiving the optical signal, and
converting it into an electrical signal.
5.1 Key Components for Optical Fiber Communications:
Optical fiber communication systems rely on a number of key components:
optical transmitters, based mostly on semiconductor lasers (often VCSELs), fiber
lasers, and optical modulators
optical receivers, mostly based on photodiodes (often avalanche photodiodes)
optical fibers with optimized properties concerning losses, guiding properties,
dispersion, and nonlinearities
dispersion-compensating modules
semiconductor and fiber amplifiers (mostly erbium-doped fiber amplifiers, sometimes
Raman amplifiers) for maintaining sufficient signal powers over long lengths of fibers,
or as preamplifiers before signal detection
optical filters (e.g. based on fiber Bragg gratings) and couplers
optical switches and multiplexers (e.g. based on arrayed waveguide gratings); for
example, optical add/drop multiplexers (OADMs) allow wavelength channels to be
added or dropped in a WDM system
electrically controlled optical switches
devices for signal regeneration (electronic or optical regenerators), clock recovery and
the like
Page | 14
various kinds of electronics e.g. for signal processing and monitoring
computers and software to control the system operation
5.2 Types of Transmission: (Short versus Long-Haul)
Two different transmission sceneries -one for the metro environment and one for long haul
environment-are significant. Broadly speaking, long haul is creating big pipes.
Apart from traditional voice and leased line services, new series in the short haul environment
include:-
Data storage-the service connects disc with storage medium.
Distributed application-this is made up of functions residing in separate geographical
locations, cooperating together.
Video link-this is large data pipe to carry computer traffic or a large pipe that can carry
anything.
The backbone network is the traditional long-haul network that has been around for many
years. Typical backbone networks have the following characteristics:
There are an extensive number of points where traffic is going onto or leaving the
network.
Distances of circuit transported on this network are less than 600 km
The express or super-express network, largely driven by Internet protocol (IP) traffic.
Mostly end-to-end traffic is involved, with less add/drop.
Distances of circuit transported on this network are greater than 1000 km.
Page | 15
6. MULTIPLEXING
In telecommunications and computer networks, multiplexing (sometimes contracted to
muxing) is a method by which multiple analog message signals or digital data streams are
combined into one signal over a shared medium. The aim is to share an expensive resource.
The multiplexed signal is transmitted over a communication channel, which may be a physical
transmission medium (e.g. a cable). The multiplexing divides the capacity of the low-level
communication channel into several high-level logical channels, one for each message signal
or data stream to be transferred. A reverse process, known as demultiplexing, can extract the
original channels on the receiver side.
A device that performs the multiplexing is called a multiplexer (MUX), and a device that
performs the reverse process is called a demultiplexer (DEMUX or DMX).
6.1 Types of Multiplexing:
6.1.1 Frequency-division multiplexing
Frequency-division multiplexing (FDM) is inherently an analog technology. FDM
achieves the combining of several signals into one medium by sending signals in several
distinct frequency ranges over a single medium.
Page | 16
A variant technology, called wavelength-division multiplexing (WDM) is used in
optical communications.
6.1.2 Time-division multiplexing
TDM involves sequencing groups of a few bits or bytes from each individual input
stream, one after the other, and in such a way that they can be associated with the
appropriate receiver.
6.1.3 Code-division multiplexing
Code division multiplexing (CDM) or spread spectrum is a class of techniques where
several channels simultaneously share the same frequency spectrum, and this spectral
bandwidth is much higher than the bit rate or symbol rate.
Page | 17
6.2 Time Division Multiplexing:
Time-division multiplexing (TDM) is a method of transmitting and receiving independent
signals over a common signal path by means of synchronized switches at each end of the
transmission line so that each signal appears on the line only a fraction of time in an alternating
pattern. This form of signal multiplexing was developed in telecommunications for telegraphy
systems in the late 1800s, but found its most common application in digital telephony in the
second half of the 20th century.
Each voice time slot in the TDM frame is called a channel. In European systems, standard
TDM frames contain 30 digital voice channels (E1), and in American systems (T1), they
contain 24 channels. Both standards also contain extra bits (or bit time slots) for signalling and
synchronization bits.
Multiplexing more than 24 or 30 digital voice channels is called higher order multiplexing.
Higher order multiplexing is accomplished by multiplexing the standard TDM frames.
There are three types of synchronous TDM: T1, SONET/SDH, and ISDN.
Plesiochronous digital hierarchy (PDH) was developed as a standard for multiplexing higher
order frames. PDH created larger numbers of channels by multiplexing the standard Europeans
30 channel TDM frames. This solution worked for a while; however PDH suffered from several
inherent drawbacks which ultimately resulted in the development of the Synchronous Digital
Hierarchy (SDH). The requirements which drove the development of SDH were these:
Be synchronous – All clocks in the system must align with a reference clock.
Be service-oriented – SDH must route traffic from End Exchange to End Exchange
without worrying about exchanges in between, where the bandwidth can be reserved at
a fixed level for a fixed period of time.
Allow frames of any size to be removed or inserted into an SDH frame of any size.
Easily manageable with the capability of transferring management data across links.
Provide high levels of recovery from faults.
Page | 18
Provide high data rates by multiplexing any size frame, limited only by technology.
Give reduced bit rate errors.
SDH has become the primary transmission protocol in most PSTN networks. It was developed
to allow streams 1.544 Mbit/s and above to be multiplexed, in order to create larger SDH frames
known as Synchronous Transport Modules (STM). The STM-1 frame consists of smaller
streams that are multiplexed to create a 155.52 Mbit/s frame. SDH can also multiplex packet
based frames e.g. Ethernet, PPP and ATM.
While SDH is considered to be a transmission protocol (Layer 1 in the OSI Reference Model),
it also performs some switching functions. The most common SDH Networking functions are
these:
SDH Cross-connect – The SDH Cross-connect is the SDH version of a Time-Space-
Time cross-point switch. It connects any channel on any of its inputs to any channel on
any of its outputs. The SDH Cross-connect is used in Transit Exchanges, where all
inputs and outputs are connected to other exchanges.
SDH Add-Drop Multiplexer – The SDH Add-Drop Multiplexer (ADM) can add or
remove any multiplexed frame down to 1.544Mb. Below this level, standard TDM can
be performed. SDH ADMs can also perform the task of an SDH Cross-connect and are
used in End Exchanges where the channels from subscribers are connected to the core
PSTN network.
SDH Regenerator – Traditional regenerators terminate the section overhead, but not
the line or path. Regenerators extend long-haul routes in a way similar to most
regenerators, by converting an optical signal that has already travelled a long distance
into electrical format and then retransmitting a regenerated high-power signal.
This diagram shows what an SDH link looks like.
SDH network functions are connected using high-speed optic fibre. Optic fibre uses light pulses
to transmit data and is therefore extremely fast. Modern optic fibre transmission makes use of
wavelength-division multiplexing (WDM) where signals transmitted across the fibre are
Page | 19
transmitted at different wavelengths, creating additional channels for transmission. This
increases the speed and capacity of the link, which in turn reduces both unit and total costs.
6.3 SDH Frame:
The STM-1 (Synchronous Transport Module, level 1) frame is the basic transmission format
for SDH—the first level of the synchronous digital hierarchy. The STM-1 frame is transmitted
in exactly 125 µs, therefore, there are 8,000 frames per second on a 155.52 Mbit/s OC-3 fiber-
optic circuit. The STM-1 frame consists of overhead and pointers plus information payload.
The first nine columns of each frame make up the Section Overhead and Administrative Unit
Pointers, and the last 261 columns make up the Information Payload. The pointers (H1, H2,
H3 bytes) identify administrative units (AU) within the information payload. Thus, an OC-3
circuit can carry 150.336 Mbit/s of payload, after accounting for the overhead.
Carried within the information payload, which has its own frame structure of nine rows and
261 columns, are administrative units identified by pointers. Also within the administrative
unit are one or more virtual containers (VCs). VCs contain path overhead and VC payload. The
first column is for path overhead; it is followed by the payload container, which can itself carry
other containers. Administrative units can have any phase alignment within the STM frame,
and this alignment is indicated by the pointer in row four.
The section overhead (SOH) of a STM-1 signal is divided into two parts:
Regenerator section overhead (RSOH) and
Multiplex section overhead (MSOH)
Page | 20
The overheads contain information from the transmission system itself, which is used for a
wide range of management functions, such as monitoring transmission quality, detecting
failures, managing alarms, data communication channels, service channels, etc.
Overall STM frame is divided into two components:
6.3.1. Transport overhead: The transport overhead is used for signalling and measuring
transmission error rates, and is composed as follows:
6.3.1.1 Section overhead: Called RSOH (regenerator section overhead) in SDH
terminology: 27 octets containing information about the frame structure required by the
terminal equipment.
6.3.1.2 Line overhead: Called MSOH (multiplex section overhead) in SDH: 45 octets
containing information about error correction and Automatic Protection Switching
messages (e.g., alarms and maintenance messages) as may be required within the
network. The error correction is included for STM-16 and above.
6.3.1.3 AU Pointer: Points to the location of the J1 byte in the payload (the first byte
in the virtual container).
This diagram shows what the STM1 Section Overhead (SOH) looks like.
6.3.2. Path virtual envelope: Data transmitted from end to end is referred to as path data. It is
composed of two components:
6.3.2.1 Payload overhead (POH): Nine octets used for end-to-end signalling and error
measurement.
Page | 21
6.3.2.2 Payload: User data (774 bytes for STM-0/STS-1, or 2,340 octets for STM-
1/STS-3c)
6.4 SONET/SDH Data Rates:
SONET/SDH Designations and bandwidths
SONET
Optical
Carrier level
SONET frame
format
SDH level and
frame format
Payload
bandwidth
(kbit/s)
Line rate
(kbit/s)
OC-1 STS-1 STM-0 50,112 51,840
OC-3 STS-3 STM-1 150,336 155,520
OC-12 STS-12 STM-4 601,344 622,080
OC-24 STS-24 _ 1,202,688 1,244,160
OC-48 STS-48 STM-16 2,405,376 2,488,320
OC-192 STS-192 STM-64 9,621,504 9,953,280
OC-768 STS-768 STM-256 38,486,016 39,813,120
6.5 SDH Network in RailTel:
RailTel has built state of the art backbone network using latest SDH technology. More than
400 important cities covering over 28,000 RKMs across the country are connected on backbone
network with STM-16 (2.5 Gbps) connectivity presently.
Backbone network have been configured in multiple ‘self-healing’ ring architecture which
provide for redundancy by automatically redirecting traffic away from failed/ de-graded route
for fault-free service. The network supports SNCP and MS-Spring protection schemes. The
network has been designed in such a way that full redundancy is available for bandwidth
between any two points.
Page | 22
Page | 23
7. REFERENCES
http://www.railtelindia.com/
http://en.wikipedia.org/wiki/RailTel_Corporation_of_India
http://searchnetworking.techtarget.com/definition/SDH
http://en.wikipedia.org/wiki/Synchronous_optical_networking
http://www.cisco.com/c/en/us/support/docs/optical/synchronous-digital-hierarchy-sdh/28327-
sdh-28327.html
http://www.dsp.pub.ro/leonardo/ipa/Chapter1/Level1/SubChapter1.7/Subchapter1_7.htm
http://www.rp-photonics.com/optical_fiber_communications.html