PROJECT REPORT

ON

INDUSTRIAL TRAINING

UNDERGONE IN

‘Northern Telecom Region’ AT KAROL BAGH New Delhi

SUBMITTED BY:

AJAY KUMAR (264600)

E&C 6TH SEMESTER G.T.B.P.I VASANT VIHAR N.D-57.

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CONTENTS

INTRODUCTION ACKNOWLEDGEMENT CONCLUSION COMPANY OVERVIEW TRANING CERTIFICATE CERTIFICATE SDH COCEPTS INSTRUMENTS USED BY BSNL IN SDH SOFTWARE USED TO PERFORM SDH

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INTRODUCTION

OBJECTIVE OF TRAINING

For a number of years, it has become the fashion as well as need to develop your skills in technical exploration and ingrains in you as a habit . This habit becomes your lifelong ally in the race to stay on top of the situation. In the ever-changing industry, the ability to explore and assimilate new knowledge is vital. Therefore, for making us up to date, confident, self-reliant, potential power to cope with the problems creatively and introducing us to the live, real practical scenario of the programming world and also bringing many interesting experiences in its wake which aims at imparting quality technical knowledge and education and innate talent with experiences, the college organized a project centric curriculum in the form of summer training which was really progressive to achieve the desired excellence in implementation of learning and self-confidence.

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ACKNOWLEDGEMENT

It is pleasure to acknowledge my debt to the many people involved, directly or indirectly, in the production of this project. I would like to thank my project manager Mr. ANIL ARORA, who devoted painstaking hours for this assignment, providing the motivational guidance during the entire preparation of this project, answering a number of my technical queries and despite their schedule, always gave time for checking the progress report.I would also like to express my sincere thanks to MR. KPS AHULWALIA, training and placement officer of our college, whose valuable guidance and timely help proved extremely fruitful.

I gratefully acknowledge the efforts of several of my colleagues who offered many suggestions throughout this project. Their constructive criticism and timely review have resulted in several improvements.

Thanks a lot for your guidance and support

SUBMITTED BY:

AJAY KUMAR (264600)

E&C 6TH SEMESTER G.T.B.P.I VASANT VIHAR N.D-57.

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CONCLUSION

Through this project centric training, I have got an insight about the real practical scenario of engineering world, which has enabled me to learn so much. In the ever-changing industry, the ability to explore and assimilate new knowledge is vital. The training period allocated to me, helped me in developing knowledge about telecommunication network. Training in this project has not only made me up-to-date, confident and self-reliant but has also enlightened me in knowing about the professional aspects of reputed telecom company like BHARAT SANCHAR NIGAM LIMITED (BSNL).

FUNDAMENTAL CANONS

Training also helped me in learning the professional ethics which engineers, in the fulfillment of their professional duties, shall:1. Hold paramount the safety, health and welfare of the public.

2. Perform services only in areas of their competence.

3. Issue public statements only in an objective and truthful manner.

4. Act for each employer or client as faithful agents or trustees.

5. Conduct themselves honorably, responsibly, ethically, and lawfully so as to enhance the honor, reputation, and usefulness of the problem.

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COMPANY OVERVIEW

Bharat Sanchar Nigam Limited(BSNL) is one of the major telecom giants in the Telecom sector. Today, BSNL is the No. 1 Telecommunications Company and the largest Public Sector Undertaking of India and its responsibilities include improvement of the already impeccable quality of telecom services, expansion of telecom network, introduction of new telecom services in all villages and instilling confidence among its customers. On October 1, 2000 the Department of Telecom Operations, Government of India became a corporation and was christened as BSNL.

Responsibilities that BSNL has managed to shoulder remarkably, deftly. Today with a 43million line capacity, 99.9% of its exchanges digital, nation wide Network management & surveillance system (NMSS) to control telecom traffic and nearly 3,55,632 route kms of OFC network, Bharat Sanchar Nigam Ltd is a name to reckon with in the world of connectivity. Along with its vast customer base, BSNL's financial and asset bases too are vast and strong. Consider the figures, as they speak volumes on  BSNL's standing:

The telephone infrastructure alone is worth about Rs. 1,00,000 crore(US $ 21.2 billion)

Turnover of Rs. 22,000 crore ( US $ 4.6 billion)

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TRAINING CERTIFICATE

Mr. AJAY KUMAR, a student of GURU TEGH BAHADUR POLYTECNIC INSTITUTE, VASANT VIHAR NEW DELHI -57, has successfully completed his SDH OFC practical training of BSNL ‘Northern Telecom Region’ at New Delhi held from 27TH

JAN, 2009 to 10th MARCH, 2009. During the practical training the behavior and performance of the student was excellent.

We wish his success in life.

(Mr. ANIL ARORA) Sr. Sub Divl. Engr. (OFC)

BSNL K.B.-II

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CERTIFICATE

THIS IS TO CERTIFY THAT THE INDUSTRIAL TRANING REPORT BASED ON TRANING UNDER GONE “BSNL” BY THE STUDENT OF UNDER MENTIONED FINAL YEAR ELECTRONICS & COMMUNICATION IS A RECORD OF BONAFIED WORK CARRIED OUT BY HIM UNDER MY SUPERVISON & GUIDANCE .

NAME : AJAY KUMARROLL NO : 264600

(SIGNATURE)

SDH CONCEPTS

INTRODUCTION

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Synchronous Digital Hierarchy (SDH) signals the beginning of a new phase in the evolution of the world’s communication network. SDH will bring a revolution in telecommunications services which will have far reaching effects for end-users, service-providers and equipment manufacturers alike. With the introduction of SDH, the transmission network will enter a new era which can be compared in scale to that occurred following the introduction of PCM and Optical Fibre.

As end-users (particularly business-users) become more dependent on effective communication, pressure builds up for a reliable and a flexible network with unlimited bandwidth. The complexity of current network, based on plesiochronous transmission systems, meant that network operators are unable to meet this demand.

The current Plesiochronous Digital Hierarchy (PDH) evolved in response to the demand for plain voice telephony (sometimes called POTS- Plain Old Telephony Service) is not ideally suited to the efficient delivery and management of high bandwidth connections. Synchronous transmission systems address the shortcomings of PDH. Using essentially the same fibre, a synchronous network is able to significantly increase available bandwidth while reducing the amount of equipment in the network. In addition the provision within the SDH for sophisticated network management introduces significantly more flexibility into the network.

Deployment of synchronous transmission systems will be straightforward due to their ability to interwork with existing plesiochronous systems. The SDH defines a structure which enables plesiochronous signals to be combined together and encapsulated within a standard SDH signal. This protects network operators’ investment in plesiochronous equipment, and enables them to deploy synchronous equipment in manner suited to the particular needs of their network.

As synchronous equipment becomes established within the network the full benefits it brings will become apparent. The network operator will experience significant cost savings associated with reduced amount of hardware in the network, and

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the increased efficiency and reliability of the network will lead to savings resulting from a reduction in operation and maintenance costs.

The sophisticated network management capabilities of a synchronous network will give a vast improvement in control of transmission networks. Improved network restoration and reconfiguration capabilities will result in better availability, and faster provisioning of services.

The SDH offers network operators a future proof network solution. It has been designed to support future services such as Metropolitan Area Network (MAN), Broadband ISDN, etc.

EVOLUTION OF SDH

PDH (Plesiochronous Digital Hierarchy) has reached a point where it is no longer sufficiently flexible or efficient to meet the demands being placed on it. As a result, synchronous transmission was thought to overcome the problems associated with plesiochronous transmission, in particular the availability of PDH to extract individual circuits from high capacity systems without having to demultiplex the whole system.

Attempts to formulate a set of standards covering optical transmission of synchronous signals began in U.S. at the beginning of 1984. The aim was to have a synchronous standard to allow the interconnection of equipment from more than one vendor. In order to move away from proprietary interfaces and achieve true inter-connectivity between vendors, subcommittee

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T1X1 of the American National Standards Institute (ANSI) began work in 1985 on developing a Standard Optical NETwork (SONET) based on a proposal by Bell Core.

In 1986, CCITT became interested in the work being carried out on SONET and after much debate on how to incorporate both U.S. and European transmission hierarchies, final agreement was reached in Feb’1988 and CCITT working group XVIII brought out the recommendations on Synchronous Digital Hierarchy (SDH), published in the CCITT Blue Book 1989. Since then, an ongoing standards effort has continued to develop and refine the SDH standards.

What is SDH ?

As defined in CCITT recommendations “the SDH is a hierarchical set of digital transport structures, standardized for the transport of suitably adapted payloads over physical transmission networks”.

The ITU-T recommendations define a number of transmission rates within the SDH. The first of these is 155 Mbit/s, normally referred to as STM-1 (where STM stands for ‘Synchronous Transport Module’). Higher transmission rates of STM-4 (622 Mbit/s), STM-16 (2.4 Gbit/s) and STM-64 (10 Gbit/s) are also defined.

The recommendations also define a multiplexing structure whereby an STM-1 signal can carry a number of lower bit rate signals as payload, thus allowing existing PDH signals to be carried over a synchronous network. This process will be explained in more detail further.

EXISTING NETWORK

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The type of transmission network that exists till today before adoption of SDH is Plesiochronous Digital Hierarchy (PDH) and it is called so because the type of signal that are processed is Plesiochronous. The PDH multiplexing hierarchy shown in Figure I appears simple enough. But there are complications encountered in processing, while multiplexing a number of 2Mbit/s channels: likely to have been created by different pieces of equipment, each generating a slightly different bit rate. Thus, before 2Mbit/s channels can be multiplexed (bit interleaved) they must all be brought up to the same bit rate by adding ‘dummy’ information bits also known as ‘justification bits’. The justification bits are indicated by justification control bits and are discarded by the demultiplexer. This process is known as plesiochronous operation as shown in Figure II.

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The same problems with synchronization as described above occur at every level of the multiplexing hierarchy and justification bits are added at each stage. The use of plesiochronous operation throughout the hierarchy has led to adoption of the term “Plesiochronous Digital Hierarchy” or PDH.

LIMITATIONS OF PDH

The availability of cheap transmission bandwidth has led to the proliferation of new, non-voice, telephone service, mostly aimed at business customer. Often, businesses rely on these services to maintain a competitive edge, and this has led business users to demand ever-improved transmission quality, higher availability of service and more flexible connection patterns.

The problem of flexibility in a plesiochronous network is illustrated by considering what a network operator needs to do in order to provide business customer with a 2Mbit/s-leased line. If a high-speed channel passes near the customer, the operation of providing him with a single 2Mbit/s line from within that channel would not be so simple.

The use of justification bits at each level in a PDH means that identifying the exact location of the frames of a single 2Mbit/s

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line with say a 140Mbit/s channel must be completely demultiplexed to its 64 constituent 2Mbit/s line via 34and 8 Mbit/s as shown in Figure III. Once the required 2Mbit/s line has been identified and extracted, the channels must then be remultiplexed back up to 140Mbit/s.

BENEFITS OF SDH

Synchronous transmission overcomes the limitations experienced in plesiochronous network. It allows the network to evolve to meet the new demands being placed upon it. SDH offers a number of benefits, both to telecom network operators and to the end users.

NETWORK SIMPLIFICATION

One of the main benefits seen by a network operator is the network simplification brought about through the use of synchronous equipment. A single synchronous multiplexer can perform the function of the entire plesiochronous “multiplexer mountain”, leading to significant reduction in amount of equipment used. Lower operating costs will also result through reductions in space inventory required, simplified maintenance, reductions in floor space required by the equipment and lower power consumptions.

The more efficient “drop and insert” of channels offered by an SDH network, together with its powerful network management capabilities, will lead to greater ease in provisioning of high bandwidth.

SURVIVABILITY

The deployment of optical fibre throughout the network and adoption of the SDH network elements makes end-to-end

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monitoring and maintenance possible. The management capability of the synchronous network will enable the failure of links or even nodes to be identified immediately.

SOFTWARE CONTROL

Provision of network management channels within the SDH frame structure means that a synchronous network will be fully software controllable. Network management systems will not only perform traditional event management dealing with alarms in the network, but will also provide a host of other functions, such as performance monitoring, configuration management, resource management, network security, etc.

The possibility of remote provisioning and centralized maintenance will mean a great saving in time spent by maintenance personnel in traveling to remote sites and this amounts to expense saving.

BANDWIDTH ON DEMAND

In a synchronous network it will be possible to dynamically allocate network capacity or bandwidth on demand. Users anywhere within the network will be able to subscribe at very short notice to a service offered over the network some of which may require large amounts of bandwidth; for example dial-up video conferencing and many other new services. These will represent new sources of revenue for network operators and increased convenience for users.

FUTURE PROOF NETWORKING

SDH offers future proof platform for new services. It is the ideal platform for services ranging from POTS, ISDN and mobile radio through to data communications (LAN, WAN, etc.). It is able to handle very latest services such as video on demand and digital video broadcasting via ATM. SDH has been selected as the bearer network for the next generation of telecommunication network, the broadband ISDN (B-ISDN).

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STANDARDISATION

The SDH standards mean that transmission equipment from different manufacturer can inter work on same line. The ability to achieve this so-called “mid-fibre meet” has come about as a result of standards which define fibre-to-fibre interfaces at the physical (photogenic) level. They determine the optical line rate, wavelength, power levels, pulse shapes and coding. Frame structure overhead and payload mappings are also defined.

This standardisation of equipment and interfaces in the SDH means network operators have freedom to choose different equipment from different vendors. This means that operators can avoid the problems traditionally associated with being locked to a proprietary solution from a single vendor. The SDH standards also facilitate inter working between North American and European transmission hierarchies.

PRINCIPLES OF THE SYNCHRONOUS DIGITAL HIERARCHIES

Despite its obvious advantages over the PDH, SDH would have been unlikely to gain acceptance if its adoption had immediately made all existing PDH equipments obsolete. All plesiochronous signals between 1.5 Mbit/s and 140 Mbit/s can be accommodated except 8 Mbit/s. The ways in which they can be combined to form a basic transmission rate of 155.52 Mbit/s is defined in ITU-T Recommendation G.709. The input signals are processed to have a basic frame called the synchronous transport module (STM-1). Figure IV shows the multiplexing structure as recommended by ITU-T.

The SDH defines a number of “containers” each corresponding to a existing plesiochronous rate. Information from the plesiochronous container is mapped into the relevant container. The way in which this is done is similar to the bit stuffing procedure carried out in a conventional PDH multiplexer. Each container then added with some control information known as

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“path overhead”. The path overhead bytes allow the operator to achieve end-to-end path monitoring; such as error monitoring. The container and the path overhead together form a “Virtual Container (VC).

In Synchronous network, all equipment is synchronized to an overall network clock. It is important to note, however, that the delay associated with a transmission link may vary with time. As a result, the location of virtual containers within an STM-1 frame may not be fixed. These variations are accommodated by associating a pointer to each VC. The pointer indicates the position of the beginning of the VC in relation to an STM-1 frame. It can be incremented or decremented as necessary to accommodate changes in the position of the VC.

ITU-T recommendation G.709 defines different combinations of Virtual Containers which can be used to fill up the pay load area of an STM-1 frame. The process of loading containers and attaching overhead is repeated at several levels in the SDH, resulting in the “nesting” of smaller VC’s within larger ones. This process is repeated until the largest size of VC (VC-4 in India) is filled, and this is then loaded into the payload of the STM-1 frame. When the payload area of STM-1 frame is full, some more control information bytes called “Section Overhead” are added. The section overhead bytes are so called because they remain with the payload for the fibre section between two synchronous multiplexers. Their purpose is to provide communication channels for functions such as OA&M facilities, protection switching, performance monitoring, frame alignment and a number of other functions.

When a higher transmission rate than the 155Mbit/s (STM-1) is required in a synchronous network is achieved by using a relatively straightforward byte-interleaved multiplexing scheme. Following hierarchy levels are defined in the SDH:

STM-1 : 155.52 Mbit/s STM-4 : 622.08 Mbit/s STM-16 : 2,488.32 Mbit/s STM-64 : 9,953.28 Mbit/s

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SDH FRAME STRUCTURE

A basic STM frame is represented by a matrix of 9rows and 270 columns; each column being one byte as shown in Figure V. Transmission is row by row, starting with the byte in the upper left corner and ending with the byte in the lower right corner. The frame repetition rate is 125 s, meaning that a byte in the payload represents a 64 Kbit/s channel.

The STM-1 frame is capable of transporting any PDH tributary signal (≤ 140 Mbit/s). The frame comprises of section overhead (SOH), pointer and the payload. How do we arrive at the bit-rates? We may proceed through the steps as given below:

Number of rows in a frame = 9 Number of columns in a frame = 9+261 = 2,70 Number of bytes/frame = 9*270 = 2,430 Number of bits/frame = 9*270*8 = 1,944 Number of bits per second = 9*270*8*8000 = 15,552,000

= 155.52 Mbit/s

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SECTION OVERHEAD (SOH)

The first 9 bytes in each of the 9 rows are called Section Overhead (SOH). SOH bytes are used for communication between adjacent pieces of synchronous equipment. SOH is classified as the Regenerator Section Overhead (RSOH) and Multiplex Section Overhead (MSOH). Top three rows of SOH are RSOH, used for the needs of the regenerator section. Bottom five rows of SOH are MSOH, used for the needs of multiplex section. The reason for this is to couple the functions of certain overhead bytes to the network architecture.

The purpose of individual bytes is detailed below:

A1,A2 : Frame alignmentB1,B2 : Parity bytes for error monitoringD1…D3 : Data Communication Channel (DCC) network managementD4…D12 : Data Communication Channel (DCC) network managementE1,E2 : Orderwire Channel F1 : MaintenanceJ0 : Trace IdentifierK1,K2 : Automatic Protection Switching (APS) channelM1 : Transmission error acknowledgement

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S1 : Clock quality indicator • : Media Dependent Bytes

In SDH, multiplexers perform both multiplexing and line terminating functions. Synchronous multiplexers can accept a wide range of tributaries and can offer a number of possible output data rates. Though the regeneration of signals is similar to PDH, there are some additional equipment in SDH to perform function like cross-connection and OA&M as explained further.

TERMINAL MULTIPLEXERS

Terminal Multiplexers are used to combine plesiochronous and synchronous input signals into higher bit rate STM-N signals as shown in Figure VI On the tributary side, all current plesiochronous bit rates can be accommodated. On the aggregate, or line side we have higher bit rate STM-N signals.

TERMINAL MULTIPLEXERS

STM-N PDH

SDH

Figure IV Terminal Multiplexer

ADD DROP MULTIPLEXERS

Plesiochronous and lower bit rate synchronous signals can be extracted from or inserted into high speed SDH bit streams by means of ADM’s. This feature makes it possible to set up ring structures, which have the advantage that automatic backup path switching is possible using elements in the ring in the event of a fault.

ADD/DROP MULTIPLEXERSTM-

NSTM-N

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PDH SDH Figure V Add/Drop Multiplexer

DIGITAL CROSS CONNECTS (DXC)

Cross-connection in a synchronous network involves setting up semi-permanent interconnections between different channels enabling routing to be performed down to VC level. This network element can have widest range of functions such as mapping of PDH tributary signals into virtual containers and switching of various containers up to and including VC-4.

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REGENERATORS

Regenerators, as the name implies, have the job of regenerating the clock and amplitude of the incoming data signals that have been attenuated and distorted by dispersion. They derive their clock signals from the incoming data stream. Messages are received by extracting various 64Kbit/s channels (e.g. service channels E1, F1, etc. in RSOH) and also can be output using these channels.

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NETWORK MANAGEMENT SYSTEM

The network management system is considered as an element in the synchronous network. All the SDH network elements mentioned so far are software-controlled. This means that they can be monitored and remotely controlled, which precisely is the job of NMS.

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NETWORK TOPOLOGY

We have already discussed various elements which can be seen in a SDH network. Elements such as Terminal Multiplexer, Add and Drop Multiplexer and Digital Cross Connects have similar functions to the extent that they provide interface for transportation of tributary signals. These elements can be used in a number of configurations. In other words, the way they are connected in a network is known as Network Topology. Some commonly used topologies are explained further.

POINT TO POINT TOPOLOGY

In Point-to-Point Topology two terminal multiplexers are connected directly as shown in Figure VII. It is no doubt simple and cost effective; but lacks the benefits of other topologies.

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POINT TO MULTIPOINT TOPOLOGY

In Point-to-Multipoint Topology two terminal multiplexers are connected via ADM or DXC to provide drop and insert at ADM location as shown in Figure VIII.

RING TOPOLOGY

In Ring topology the elements used are ADM’s connected together in ring form, as shown in Figure IX; though DXC’s can also be used. Apart from the facility of drop and insert possible at every ADM locations, this topology provides a special feature called “Self Healing”. This feature protects

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the traffic carried by the ring automatically against equipment/fibre failure; and hence is most commonly used topology.

SYNCHRONOUS MULTIPLEXING

INTRODUCTION

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Present transmission systems interconnecting switches use multiplexers, whom input as well as the output are plesiochronous signals. These are commonly known as Plesiochronous Digital Hierarchy (PDH) multiplexers. Transmission systems planned for the future will use multiplexers that accept plesiochronous\synchronous signal at its input and synchronous signal at the output and are called Synchronous Digital Hierarchy (SDH) multiplexers.

This handout explains in a simplified manner the principles of synchronous multiplexing and narrates various signal processing steps by taking different input signals from PDH.

TERMINOLOGY & DEFINITIONS

1. SYNCHRONOUS DIGITAL HIERARCHY (SDH)

SDH is a hierarchical set of digital transport structures, standardized for the transport of suitably adapted payloads over physical transmission networks.

2. SYNCHRONOUS TRANSPORT MODULE (STM)

An STM is the information structure used to support section layer connections in the SDH. It consists of information payload and section overhead information fields organized in a block frame structure, which repeats every 125 s. The information is suitably conditioned for serial transmission on the selected media at the rate, which is synchronized to the network. A basic STM is defined at 1,55,520 Kbit/s. This is termed STM-1. Higher capacity STM’s are formed at rate equivalent to N times this basic rate. STM capacities for N= 4, N= 16 and N= 64 are defined by ITU-T.

3. VIRTUAL CONTAINER-n (VC-n)

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A virtual container is the information structure used to support path layer connections in the SDH. It consists of information payload and Path Overhead (POH) information fields organized in a block frame structure, which repeats every 125 or 500 s. Alignment information to identify VC-n frame start is provided by the server network layer. Two types of virtual containers have been identified.

LOWER ORDER VIRTUAL CONTAINER- n : VC-n (n= 1,2,3)

This element comprises a single Container-n (n= 1,2,3) plus the lower order Virtual Container POH appropriate to that level.

HIGHER ORDER VIRTUAL CONTAINER- n : VC-n (n= 3,4)This element comprises either a single Container-n (n= 3,4) or an assembly of Tributary Unit Groups (TUG 2s or TUG 3s) together with Virtual Container POH appropriate to that level.

4. ADMINISTRATIVE UNIT-n (AU-n)

An administrative unit is the information structure which provides adaptation between the higher order path layer and the multiplex section layer. It consists of an information payload (the higher order Virtual Container) and an Administrative Unit pointer which indicates the offset of the payload frame start relative to the multiplex section frame start.

The AU-4 consists of a VC-4 plus an Administrative Unit pointer which indicates the phase alignment of the Vc-4 with respect to an STM-N frame. One or more Administrative units occupying fixed, defined positions in an STM payload are termed as Administrative Unit Group (AUG). An AUG consists of a homogeneous assembly of AU-4.

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5.TRIBUTARY UNIT-n (TU-n)

A Tributary Unit is an information structure which provides adaptation between the lower order path layer and the higher order path layer. It consists of an information payload (the lower order virtual container) and a Tributary Unit pointer which indicates the offset of the payload frame start relative to the higher order Virtual Container frame start.

The TU-n (n= 1,2,3) consists of a VC-n together with a Tributary Unit pointer. One or more Tributary Units, occupying fixed, defined position in a higher order VC-n payload is termed a Tributary Unit Group (TUG). TUG’s are defined in such a way that mixed capacity payloads made up of different size Tributary Units can be constructed to increase flexibility of the transport network.

A TUG-2 consists of a homogeneous assembly of identical TU-1s or Tu-2.A TUG-3 consists of a homogeneous assembly of TU-2s or TU-3.

6.CONTAINER-n (n= 1…4)

A container is the information structure which forms the network synchronous information payload for a Virtual Container. For each of the defined Virtual Containers there is a corresponding container.

7.NETWORK NODE INTERFACE (NNI)

The interface at the network node which is used to interconnect with another network container.

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8.POINTER

An indicator whose value defines the frame offset of a Virtual Container with respect to the frame reference of the transport entity on which it is supported.

9.CONCATENATION

A procedure whereby a multiplicity of Virtual Containers is associated with one another with the result that their combined capacity can be used as a single container across which bit sequence integrity is maintained.

10. SDH MAPPING

A procedure by which tributaries are adapted into Virtual Containers at the boundary of an SDH network.

11.SDH MULTIPLEXING

A procedure by which multiple lower order path layer signals are adapted into a higher order path or the multiple higher order path layer signals are adapted into a multiplex section.

12. SDH ALIGNING

A procedure by which the frame offset information is incorporated into the Tributary Unit or the Administrative Unit when adapting to the frame reference of the supporting layer.

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INPUT TO MULTIPLEXER

The basic input to a synchronous multiplexer is plesiochronous signal from European or North American or Japanese hierarchy and basic output is synchronous signal called Synchronous Transport Module of level one (STM-1). As European standards for PDH working is followed in India, let us consider only European standards for PDH rates for explanation. The SDH multiplexer only accepts only following PDH bit rates from European hierarchy:

2,048 Kbit/s 34,368 Kbit/s 1,39 264 Kbit/s

SDH does not accept 8,448 Kbit/s PDH signal.

PRINCIPLES OF SYNCHRONOUS MULTIPLEXING

The SDH defines a number of containers at its boundary; each corresponding to an existing plesiochronous rate. These containers are filled in with the information from a plesiochronous signal, the process is called mapping. The way in which this is done is similar to the justification procedure carried out in PDH multiplexing.

Each container is then added with control information known as Path Overhead which is to help the service provider to achieve end to end path monitoring. The container and the path overhead

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together is called Virtual Container. Depending upon the PDH bit rates various VC’s are formed. For example, VC-1,VC-3,VC-4 are formed for European PDH bit rates 2 Mb/s, 34 Mb/s and 140 Mb/s respectively.

In a synchronous network, all equipment is synchronized to an overall network clock. However there may be a slight delay associated with a transmission link; the location of VC’s within an STM-1 frame may not be fixed with time. These variations are accommodated by associating a pointer with each VC, which indicates the position of the beginning of the VC with respect to the STM-1 frame. The pointer value can be incremented or decremented as necessary to accommodate movements of the position of the VC. The VC and the pointer together is called the Administrative Unit (AU) if it contains VC-4 and Tributary Unit (TU) if it contains VC-3 or VC-1.TU’s are further combined in a definite fashion to obtain VC-4 and in turn AU-4 and AUG are obtained. Figure X shows a genetic multiplexing structure standardized by ITU-T which takes care of both American as well as European PDH rates.

Figure XI shows the reduced multiplexing structure which takes care of only European PDH hierarchy. Further some more control information bytes called Section Overhead (SDH) is added to provide communication channel for OA&M, protection switching, frame alignment, performance monitoring etc. An AUG and a section overhead together form STM-1. Details of synchronous multiplexing taking various input bit rates are explained in the following sections.

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FORMING CONTAINER C-4

As defined by ITU-T, “a container is the information structure which forms the network synchronous information payload for a Virtual Container”. Container-4 is filled out by taking 140 Mbit/s PDH signal in a manner similar to the justification process carried out in PDH higher order multiplexing. Each of the 9 rows of payload (260 columns by 9 rows) portioned into 20 blocks of 13 bytes. The first byte of each block is W\X\Y\Z containing D, R, O, S and C bits as shown in Figure XII.

The last 12 bytes of each block contain data bits (i.e. 96 D bits). In above provision each row will have one ‘S’ bit and five ‘C’ bits, where CCCCC= 00000or majority vote will indicate ‘S’ bit as data bit. The size of the C-4 is 260 columns by 9 rows (260*9 bytes) in a time frame of 125 s.

FORMING VIRTUAL CONTAINER VC-4

The container is then added with control information known as path overhead (POH) of 9 bytes (one Column by nine rows) which help the service provider to achieve end-to-end path monitoring. The container and the path overhead together is called Virtual Container (VC). VC-4 is formed when POH is added to C-4. The size of the VC-4 will be 261 columns by 9 rows (261*9 bytes) in a time frame of 125 s.

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FORMING ADMINISTRATIVE UNIT AU-4

A pointer which is physically located in 4th row of the SOH area, is associated with VC, whose value indicates the position of the beginning of the VC with respect to the STM-1 frame and the process is called SDH aligning. The pointer value can be incremented or decremented as necessary to accommodate movements of the position of the VC. The VC-4 and the pointer together is called Administrative Unit-4 (AU-4)

FORMATION OF ADMINISTRATIVE UNIT GROUP (AUG) One AU-4 moves further to form AUG without any addition of bytes. Formation of AUG may appear redundant; but its necessity may be appreciated while forming AUG from AUS-3 (applicable to SONET).

ADDING SOH TO FORM STM-1

More control information bytes called section overhead (SOH), is added to the AUG to form STM-1 frame. SOH is further classified

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as regenerator SOH (RSOH) terminated at regenerators and Multiplex SOH (MSOH) terminated where AUGs are assembled and disassembled. MSOH bytes pass transparently through regenerators. The SOH includes bytes for block framing, bytes for error performance, bytes for order-wire and other bytes to provide communication channel for OA&M, protection switching, etc.. Figure XIII depicts all the steps involved to obtain STM-1 frame from C-4.

FORMING VIRTUAL CONTAINER VC-12

The container VC-12 is added with control information of 4 bytes called path overhead to achieve end-to-end path monitoring. The C-12 and the POH together is called VC-12. The size of the VC-12 will be 140 bytes in a time frame of 500 s.

FORMING TRIBUTARY UNIT TU-12

The VC-12 together with the pointer is called Tributary Unit (TU-12). The size of the TU-12 is 144 bytes, in a multiframe (4 frame) structure, image 140 bytes are for VC-12. Two bytes (V1 and V2) out of remaining four bytes are the pointers indicating the location of the first byte (V5) of the V-12. Conceptually the size of

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TU-12 will be 36 bytes (4 columns * 9 rows) in a time frame of 125 s.

MULTIPLEXING OF TU12s TO FORM TUG-3

It is achieved in two stages. First, three TU-12s are multiplexed by byte interleaving to form one TUG-2. Second, seven numbers of TUG-2s are multiplexed to obtain TUG-3. This is depicted in Figure XIV.

The payload size of TUG-3 while multiplexing from Tu-12s via TUG-2s will be 756 bytes which accounts for 84 columns by 9 rows in a time frame of 125 s. As size of TUG-3 is 86 columns by 9 rows, the byte in extra two columns are used as Null Point Indicator (NPI) and fixed stuff. The NPI is used to distinguish between TUG-3 containing TU-3 or TUG-2s and is contained in first three bytes of the first column.

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EQUIPMENT

The software used for managing the STM I equipment is NM 2100/6300 Element Manager CT 6300 Craft Terminalwhich is developed by Fibcom Technologies, Gurgaon (Harayana)

The FIBCOM 6300 is an open ITU-T compliant TMN system. The product family covers applications ranging from craft terminals over element management systems to complex network management systems. It is divided into two main products:

FIBCOM 6300NM - the network manager with advanced network layer functions and management of network elements

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FIBCOM 6300CT - the craft terminal for local operation and maintenance.

The FIBCOM 6300 is a combined element and network management system with a Windows NT-based user interface. It is a very robust, scalable and reliable carrier-class system from which all SDH elements can be managed. A single server can handle several thousand-network elements and more servers can be added.

To put it simply, the FIBCOM 6300 involves element and network management of transmission networks including optical networks. The FIBCOM 6300 provides automated or semi-automated path setup including protection, reconfiguration of paths and grooming of paths. Paths can be related to customers - internal or external. Performance data is collected, and alarms are retrieved and related to paths.

BENEFITS

The operator can concentrate on the circuits and services without losing the visibility of and access to the individual network elements. Furthermore, the FIBCOM 6300 is highly scalable and can be configured with duplicated computer servers for extremely high availability. It provides with open interfaces (Q3) for easy integration with other management systems.

KEY FEATURES

Multiple operating platform• TMN

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• Element Manager• Craft Terminal

Distributed GUI Supports all FIBCOM products Remote SW downloads World -wide field proven Management System Management of SDH, ATM and primary rate elements Windows NT graphics user interface Distributed management platform based on CORBA Scalable, flexible and cost effective solution Configurable, fault and performance management Compliant with ITU-T and ETSI standards

NM2100 Element Manager

The 6300 EM runs under Windows NT for management of SDH, ATM, HDSL, PDH and primary rate equipment. The 6300CT runs under Windows 95 on a portable PC. Both products have a graphical user interface.

The 6300EM and the 6300CT can manage different types of equipment via element access modules. For Example,

FIBCOM 6310 & 6320 Edge Node are managed using the same 6300 System. SDH product family for regional and access networks.

FIBCOM 6330 SDH product family for trunk and regional networks.

FIBCOM 6340 SDH for multi service applications. FIBCOME 7200 Optical Transport System. (DWDM).

The 6300EM/NM can be configured as a fully distributed multi-user system with the software located on a number of computers working together as one virtual computer platform. The data

40

distribution is supported by CORBA. Together with the modular system design, the data distribution facility permits tailored management solutions with element manager configurations ranging from simple single user systems managing small networks to large multi-user management systems managing complex networks with thousands of network elements

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Instruments Used By BSNL In SDH

Fibcom India Ltd. is the leader in SDH equipment and optical fiber network solutions from concept to commissioning in technical collaboration with Tellabs Denmark A/S.Fibcom’s high quality, standards based and field proven SDH/DWDM product range can satisfy the needs of most demanding customer by virtue of its flexibility, adaptability and expandability. A range of network management system is available to suit any type of customer requirements.B.S.N.L is one of their active customers, some of the equipments used by B.S.N.L are as follows:-

1.Fibcom 6310 edge node2.Fibcom 6320 edge node3.Fibcom 6325 edge node4.Fibcom 6340 edge node5.Fibcom 6345 edge node6.Fibcom 6370 edge node

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Various Phases In SDH where Fibcom’s equipments are used

FIBCOM 6310 Edge Node

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FIBCOM 6310 Edge node is a flexible, cost-effective ADM/TM providing access for up to 21x 2 Mbit/s ITU-T G.703 services and ATM 155 Mbit/s, E3/DS3/E4 Transportation

FIBCOM 6310 is a complete SDH node, providing all the benefits of SDH, such as protection and performance monitoring with various applications in access networks

FIBCOM 6320 Edge Node

Compact STM-1, STM-4, ADM/TM network element with 4/1

connectivity for access/regional network

6320 is an acronym for Add- Drop Multiplexers and Cross Connects for VC1 level switchinexcellent choice for access and regional transport networks.

Wide range of Tributaries E1/E3/E4/STM-1/STM1e/STM1o & 10/100 Ethernet, DTMF Engineering Order Wire (EoW),

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Ultra low power consumption, Ideal for access & regional network, ATM Payload supports.

FIBCOM 6320 offers STM-1 and STM 4 optical interfaces; a special feature unique to this product is "Sub deployed lines". Which makes it possible to provide fully managed STM-1 lines Running only at third of the capacity

FIBCOM 6320 can operate over extended temperature range. It offers 2 Mb/s signals with an output jitter, which is sufficiently low to carry synchronisation signals.

FIBCOM 6325 Edge Node

Optical SDH trunk platform for multiple services

Fibcom 6325 is a compact Multi-Service Provisioning Platform supporting SDH, PDH and data services. High reliability and redundancy

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enable the node to be used not only in access networks, but also in core networks.

Small, fast and dense... fits anywhere. At only 1RU (44mm) in height. It offers speeds of up to 2.5Gbps (STM-16) and enables a wide mix of services from traditional SDH and PDH to colored WDM and IP interfaces

Cross-connection redundancy makes the Fibcom 6325 node reliable as HUB node handling high traffic load, Formed in ring or meshed networks, all traffic going through the Fibcom 6325 node is fully protected against single point of failures

FIBCOM 6370 Edge Node

High-capacity optical networking

FIBCOM 6370 provides transparent light paths, which can carry most types of traffic such as SDH/SONET, IP and ATM over SDH and a large variety of data signals (Gigabit Ethernet, Fibre Channel etc.). This, one-optical-platform-carries-all-signal-formats, allows flexible and

46

rapid in-service expansion of both capacity and services.

It can reduce infrastructure cost of long haul and regional systems. In WDM systems a single optical amplifier operates as a multi-channel repeater, as against individual regenerators required per channel in traditional single channel systems

FIBCOM 6370 provides 32/64-channel DWDM platform for operation at the ITU-T grid in C Band and L Band respectively

FIBCOM 6370 adds an additional "optical Protection layer" to the network. This layer can be used, for example, to provide protection of client signals

47

SOFTWARE USED TO PERFORM SDH

The software used for managing the STM I equipment is NM 2100/6300 Element Manager CT 6300 Craft Terminal which is developed by Fibcom Technologies, Gurgaon (Harayana).

The FIBCOM 6300 is an open ITU-T compliant TMN system. The product family covers applications ranging from craft terminals over element management systems to complex network management systems. It is divided into two main products:

FIBCOM 6300NM - the network manager with advanced network layer functions and management of network elements

48

FIBCOM 6300CT - the craft terminal for local operation and maintenance.

The FIBCOM 6300 is a combined element and network management system with a Windows NT-based user interface. It is a very robust, scalable and reliable carrier-class system from which all SDH elements can be managed. A single server can handle several thousand-network elements and more servers can be added.

To put it simply, the FIBCOM 6300 involves element and network management of transmission networks including optical networks. The FIBCOM 6300 provides automated or semi-automated path setup including protection, reconfiguration of paths and grooming of paths. Paths can be related to customers - internal or external. Performance data is collected, and alarms are retrieved and related to paths.

BENEFITS

The operator can concentrate on the circuits and services without losing the visibility of and access to the individual network elements. Furthermore, the FIBCOM 6300 is highly scalable and can be configured with duplicated

49

computer servers for extremely high availability. It provides with open interfaces (Q3) for easy integration with other management systems.

KEY FEATURES

Multiple operating platform• TMN• Element Manager• Craft Terminal

Distributed GUI Supports all FIBCOM products Remote SW downloads World -wide field proven Management

System Management of SDH, ATM and primary rate

elements Windows NT graphics user interface Distributed management platform based

on CORBA Scalable, flexible and cost effective

solution Configurable, fault and performance

management Compliant with ITU-T and ETSI standards

50

NM2100 Element Manager

The 6300 EM runs under Windows NT for management of SDH, ATM, HDSL, PDH and primary rate equipment. The 6300CT runs under Windows 95 on a portable PC. Both products have a graphical user interface.

The 6300EM and the 6300CT can manage different types of equipment via element access modules. For Example,

FIBCOM 6310 & 6320 Edge Node are managed using the same 6300 System. SDH product family for regional and access networks.

FIBCOM 6330 SDH product family for trunk and regional networks.

FIBCOM 6340 SDH for multi service applications.

FIBCOME 7200 Optical Transport System. (DWDM).

The 6300EM/NM can be configured as a fully distributed multi-user system with the software located on a number of computers working together as one virtual computer platform. The data distribution is supported by CORBA.

51

Together with the modular system design, the data distribution facility permits tailored management solutions with element manager configurations ranging from simple single user systems managing small networks to large multi-user management systems managing complex networks with thousands of network elements

52