Seminar Report

SEMINAR REPORT

On

SYNCHRONOUS DIGITAL HIERARCHY

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE OF

BACHELOR OF TECHNOLOGY

(Electronics & communication)

SUBMITTED BY

Vikram Kumar 3208190

June 2012

GANPATI INSTITUTE OF ENGINEERING ANDTECHNOLOGY-BILASPUR

KURUKSHETRA UNIVERSITY, KURUKSHETRA

CONTENTS

TITLES PAGE

NO.

1 INTRODUCTION

1.1 SDH CONCEPT

1.2 EVOLUATION OF SDH

1.2.1 WHAT IS SDH

1.2.2 EXISSTING NETWORK

1.2.2.1 LIMITATION OF THE PDH

1.2.3. BENEFITS OF THE SDH

2. NETWORK SIMPLIFICATIONS

2.1 SURVIVABILITY

2.2 SOFTWARE CONTROL

2.3 BANDWIDTH ON DEMAND

2.4 FUTURE PROOF NETWORKING

3 STANDARISATION

3.1 PRINCIPLE OF THE SDH

3.2 SDH FRAME STRUCTURE

3.3 SECTIOMN OVERHEAD

3.4 TERMINAL MULTIPLEXER

3.5 ADD AND DROP MULTIPLEXER

3.6 DIGITAL CROSS CONNECT

3.7 REGENERATORS

3.8 NETWORK MANAGEMENT SYSTEM

3.9 NETWORK TOPOLOGY

3.10 POINT TO POINT TOPOLOGY

3.11 POINT TO MULTIPORT TOPOLOGY

3.12 RING TOPOLOGY

4 SYNCHRONOUS MULTIPLEXING

4.1 INTRODUCTION

4.2 TERMINOLOGY AND DEFINATIONS

4.3 INPUT TO MULTIPLEXER

4.4 PRIMARY SYNCHRONOUS

MULTIPLEXER

1.INTRODUCTION

1.1 SDH CONCEPTS

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 straight forward 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 deploysynchronous

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 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 MetropolitanArea

Network (MAN), Broadband ISDN, etc.

1.2 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 interconnectivity between vendors, subcommittee 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.

1.2.1 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.

1.2.2 EXISTING NETWORK

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.

Diagram 1

Fig no.1 pdh mutliplexing

The PDH multiplexing hierarchy shown in Figure 1 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’.

Diagram 2

Fig 2 mapping of the pdh signal into sdh

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.

1.2.2.1 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 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 1. Once the required 2Mbit/s line has been

identified and extracted, the channels must then be remultiplexed back up to 140Mbit/s.

1.2.3 BENEFITS OF SDH

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.

2 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.

2.1 SURVIVABILITY

The deployment of optical fibre throughout the network and adoption of the SDH

network elements makes end-to-end monitoring and maintenance possible. The

management capability of the synchronous network will enable the failure of links or

even nodes to be identified immediately.

2.2 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.

2.3 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.

2.4 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).

3 . 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 problem 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.

3.1 PRINCIPLES OF THE SDH:-

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 3 shows the multiplexing structure as recommended by ITU-T. The SDH defines

a number of “containers” each corresponding to 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 “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

3.2 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 m 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?

Diagram 3

Fig sdh frame structure

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 = 2,43019

· 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

3.3 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 alignment

B1,B2 : Parity bytes for error monitoring

D1…D3 : Data Communication Channel (DCC) networkmanagement

D4…D12 : Data Communication Channel (DCC) network management

E1,E2 : Orderwire Channel

F1 : Maintenance

J0 : Trace Identifier

K1,K2 : Automatic Protection Switching (APS) channel

M1 : Transmission error acknowledgement

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.

3.4TERMINAL MULTIPLEXERS

Terminal Multiplexers are used to combine plesiochronous and synchronous input signals

into higher bit rate STM-N signals as shown in Figure 3 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.

Diagram-4

Stm-n

pdh

sdh

Figure 4 Terminal Multiplexer

3.5ADD 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.

3.6 DIGITAL CROSS CONNECTS (DXC)

Cross-connection in a synchronous network involves setting up semipermanent

interconnections between different channels enabling routing to be performed down to

VC level.

Diagram 6

Fig 6 digital cross connect switch

Terminal multiplexer

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.

3.7 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.

Diagram 7

Fig7regenerator

3.8 NETWORK MANAGEMENT SYSTEM

The network management system is considered as an element in the synchronous

network.

Fig 8 nms

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.

3.9 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 waythey

are connected in a network is known as Network Topology. Some commonly used

topologies are explained further.

3.10 POINT TO POINT TOPOLOGY

In Point-to-Point Topology two terminal multiplexers are connected directly as shown in

Figure 9. It is no doubt simple and cost effective; but lacks the benefits of other

topologies.

Diagram 9

Fig 9

3.11 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 10

Diagram 11

Fig 11

3.12 RING TOPOLOGY

In Ring topology the elements used are ADM’s connected together in ring form, as

shown in Figure 12; 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 the traffic carried by the ring automatically against

equipment/fibre failure; and hence is most commonly used topology.

Diagram 12

Fig 12

4 SYNCHRONOUS MULTIPLEXING

4.1 INTRODUCTION

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.

Diagram 13

Fig 13

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.

4.2 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 m 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 )

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 m 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 CONTAINERn

: 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.

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.

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.

4.3 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.

4.4 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

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 11 shows a genetic multiplexing structure standardized by ITU-T which takes

care of both American as well as European PDH rates. Figure12 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.

Diagram 14

Fig 14

4.5 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 14. 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 m s.

4.6 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 m s.

4.7 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)

4.8 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).

4.9 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 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 15

depicts all the steps involved to obtain STM-1 frame from C-4.

Fig 15

4.10 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 m s.

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

125 m s.

4.12MULTIPLEXING 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 16

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 m 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.

Diagram17

Fig 17

4.13 EQUIPMENT

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

· 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.

4.15 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.

4.16 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

4.17 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. 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

4.18 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:-

fig 18 Various Phases In SDH where Fibcom’s equipmentsare used

1. Fibcom 6310 edge node

2. Fibcom 6320 edge node

3. Fibcom 6325 edge node

4. Fibcom 6340 edge node

5. Fibcom 6345 edge node

6. Fibcom 6370 edge node

4.19 FIBCOM 6310 Edge Node

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 thebenefits of SDH, such as

protection and performance monitoring with various applications in access networks

4.20 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 switchin excellent 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), 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.

Diagram 19

4.21 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 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

Diagram 20

Fig 20

4.22 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-carriesall- signal-formats,

allows flexible and rapid inservice expansion of both capacity and services. It can reduce

infrastructure cost of long haul and regional systems.

Fig 21

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

4.23 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

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

FIBCOM 6300 is a combined element and network management system with a Windows

NTbased 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.

4.24 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

othermanagement systems.

4.25 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.

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. Together with the modular

system design,