seminar report
TRANSCRIPT
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,