Optical wdm networks principles and practice management

Chapter 14
Optical Network Management
Alan McGuire
Core Transport, Internet & Data Networks, OP7, B29, Adastral Park, Martlesham Haeth,
Suffolk, United Kingdom IP5 3RE. Email:
Abstract: Optical networks will play an essential role in meeting the demands for future
communications bandwidth. With such large traffic volumes at risk network
management is fundamental to the running of such networks. To achieve this
on an industrial scale management solutions must be based on an
unambiguous framework that describes the entities that need to be managed.
This chapter describes such a framework and provides a high level summary of
how it can be applied to the management of both simple and complex
structures. Nevertheless management of this new technology is still at a very
early stage and considerable effort is required within the industry before the
vision of an optical transport network can be fully realized.
1. INTRODUCTION
The accelerating demand for bandwidth fuelled by growth in both the
Internet and broadband services represents a major challenge to network
operators. Globally operators are facing up to a shortage of fiber capacity in
parts of their networks. Whereas this has been most acute in the US where
growth in traffic is greatest it is rapidly becoming an international problem.
Conventionally an operator would have increased capacity by deploying
more fiber or introducing higher bit rate digital systems. Approximately
three years ago a new option became commercially available, wavelength
division multiplexing. This technology has emerged from the research labs
302 OPTICAL WDM NETWORKS
and in a relatively short time frame has become an essential weapon in the
transmission engineer’s arsenal. Over 1000 of these systems have now been
deployed globally. Depending on the number of channels utilized WDM
increases the capacity of a fiber from between 2.5 – 10 Gbps with existing
single channel systems to between 40 and 200 Gbps. With large traffic

volumes at risk network management is an essential component of such
systems. At the present time the management of these systems is relatively
simple. In the next few years we can expect to see the introduction of more
complex optical systems such as rings and cross-connect meshes. There has
been a considerable amount of literature published regarding the
transmission characteristics of such networks but very little on the network
management challenge. Yet the lack of large scale industrial strength
management systems represents a major barrier to the deployment of the
optical network. This is particularly true in the existing competitive
environment where automation of many of the tasks involved in running and
maintaining the network will become a necessity to drive down operating
costs and to provide faster provision of services.
In this chapter we shall examine some of the features of existing optical
network management solutions and describe what will be required in order
to manage the optical transport network of the future. But first we need to
understand what it is that we want to manage.
2. OPTICAL TRANSPORT NETWORK ARCHITECTURE
In order to manage a communications network it is necessary to describe
the entities that need to be managed in a rigorous and unambiguous manner.
The integration of technology and function is now so great that it is
impossible to accurately describe what functions a network element
provides by means of a semi-formal technique. Furthermore, the
achievement of successful scalable software systems is predicated on a clear
definition of what is to be managed and its behaviour.
Transport networks can be described in terms of layer networks in
accordance with the architectural principles cited in (ITU-T
Recommendation G.805, 1995). Each layer network represents a set of
inputs and outputs (or access points) that can be interconnected and the
layer network is characterized by the information that is transported across
it. This information, or characteristic information as it is termed, is a signal

of characteristic rate, coding and format. Examples of layer networks
include the VC and VP layers in ATM, the VC-12, VC-4, multiplex and the
Optical Network Management 303
regenerator sections in SDH. A layer networks topology can be described in
terms of subnetworks and links between them, as illustrated in Figure 1.
Figure 1: Components of a layer network
A subnetwork can be decomposed into smaller subnetworks
interconnected by links, in other words it is recursive. This decomposition
can, if required go from a global network right down to the smallest
subnetwork that is equivalent to a single network elements cross-connect
fabric. Connectivity in any layer network can be managed at the network
level in the same manner independently of technology. In other words, once
we know how to manage connectivity in one layer we should be able to do it
for all layers. Managed objects that represent resources within a layer
include connection, link, subnetwork, trail, network trail termination points
(NW TTPs) and Network Connection Termination Points (NW CTPs).
These managed objects represent an abstract view of the resource that can
be manipulated by a network manager.
Layer networks have client/server relationships with each other, and in
many cases one server layer may support different types of clients (Figure
2). An example is the VC-4 network layer which can support (is the server
of) VC-3, VC-2-nc, VC-12, ATM VP etc. Whereas it can support these
304 OPTICAL WDM NETWORKS
different clients the definition of its characteristic information is separate
and distinct. In turn the VC-4 layer network is the client of the multiplex
section. To get from one layer to another requires some processing to alter
the characteristic information and this is provided by entities known as
adaptation and termination functions. Adaptation functions provide
functionality such as multiplexing/demultiplexing, frequency justification,
timing recovery, alignment and soothing. Termination functions provide

means of ensuring signal integrity supervision within a layer by means, for
example, of error detection codes, trail trace identifiers, remote indicators
and performance monitoring. The transfer of validated information is
termed a trail.
Figure 2: The client/server relationship
TCP – termination connection point, CP – connection point
In addition to providing a network view, the architecture can also be
applied to network elements where adaptation and termination functions are
combined to describe functionality as it can be observed from the inputs and
outputs of the network element. The internal structure of the implementation
(the equipment design) does not need to be identical to the structure of the
functional model as long as the external observable behaviour is the same.
Optical Network Management 305
The management view of a network element is based upon an information
model containing managed objects that can be manipulated by a
management system. The definition of a managed object is derived from a
specific part of the functional model. For example, generic trail termination
point and connection termination point classes are defined generically such
as CTP and TTP, from which technology dependent subclasses such as
rsTTP and rsCTP (in SDH) can be developed using the object oriented
principle of inheritance. These managed objects have attributes and
behaviour that is manipulated from a management system; i.e., they can
generate alarms or change their connectivity to other objects. The managed
object effectively hides the implementation of the resource that it represents
from the management systems and only provides information about aspects
of that resource which are important from a network management view.
In essence, element managers manipulate managed objects and
relationships between these managed objects within a network element,
whereas network management is concerned with entities such as network
connections, which may use resources from several network elements. The

reader is warned however that this is a very simplified picture of the reality.
ITU-T Recommendation G.872 (1995), which is a technology dependent
version of G.805, defines three optical layers, as shown in Figure 3, in the
optical transport network (OTN):
– an optical channel (OCh) layer network that provides end-to-end
networking of optical channels for transparently conveying digital client
information of varying formats (e.g., SDH, PDH and ATM)
– an optical multiplex section (OMS) layer network that provides
functionality for transport of a multi-wavelength optical signal
– an optical transmission section (OTS) layer network that provides
functionality for transmission of optical signals on optical media
306 OPTICAL WDM NETWORKS
Figure 3: The Optical transport network layers
The optical transport network architecture of G.872 is extremely flexible
and supports the following features (not all of which may appear in a single
instance of a network):
– Unidirectional, bidirectional, and point-to-multipoint connections.
– Individual optical channels within a multiplex may support different
client types.
– Cross-connection of optical channels can be accomplished by either
wavelength assignment or wavelength interchange.
– Optical transport network functionality can be integrated with client
functionality in the same equipment.
– Interworking between equipment with existing single-channel optical
interfaces (ITU-T Recommendation G.957, 1999) and equipment
containing optical transport network functionality.
Optical Network Management 307
The last two points are significant since they provide network operators
with a degree of flexibility in the design of their networks, both now and in
the future.

Each of these layer networks provides overhead for the operations
administration and maintenance of its layer. OAM functions include
continuity and connectivity supervision, defect indications (upstream and
downstream), protection switching protocols and channels for transporting
management information. Not all of these functions are found in each layer.
Initially there was considerable debate with regard to the nature of the
overhead at the optical channel level as some people viewed the optical
channel as a transparent entity within the network, but such an entity, almost
by definition cannot be managed. Instead of optical transparency the optical
channel provides service transparency, and this is perhaps more central to
the concept of optical networking as described by the ITU. The optical
channel overhead is created within a digital frame that takes the client layer
signal in the form of a continuous data stream and adds both the overhead
and a forward error correction mechanism for improving system margin.
This frame is known as a digital wrapper.
The concept of the digital wrapper can be viewed in one of two ways,
firstly as an overhead that is carried end-to-end and so may be switched in
optical channel subnetworks. However, this requires that the optical channel
remain in the optical domain from beginning to end. Alternatively at
intermediate points part, but not all, of the overhead may be processed. At
such points the optical channel is regenerated, the FEC is computed and the
relevant parts of the overhead are processed. There is however no need to
obtain access to the payload. In contrast to all optical networks, optical
transport networks utilize the strengths of both electronics and optics to
produce much more scalable networks. Nevertheless there is considerable
debate within the standards community as to the appropriate overheads and
the choice of FEC.
The following figures (4, 5 and 6) show the relationships between the
resources of the transport network and managed objects. The actual objects
are subject to change in the standards’ body and the ones provided here are

for indication purposes. With these in hand we have the basic resources of
the optical transport network that need to be managed.
308 OPTICAL WDM NETWORKS
Figure 4: Relationship between equipment resources and managed
objects. The adaptation and termination functions and their
connectivity are managed and controlled via managed objects
Optical Network Management 309
Figure 5: Relationship between optical transport resources and optical
managed objects. The example shown can be considered as an optical
channel cross-connect with two ports
310 OPTICAL WDM NETWORKS
Figure 6: Entity-Relationship between optical managed objects
3. OPTICAL NETWORK
MANAGEMENT
ARCHITECTURE
Network management is an activity that allows a network operator to
administrate, plan, provision, install, maintain, monitor and operate a
telecommunications network and its services. Within the ITU-T, the general
architecture of the management network is described in terms of a
Telecommunications Management Network (TMN) as described in
(M.3010, 1996). The TMN concept can be applied to a variety of scenarios
including public and private networks, exchanges, digital and analog
transmission systems, ISDN, circuit and cell-based networks, operations
systems, PBX’s and signalling systems. It can also be applied to optical
networking. Although there are some issues concerning the viability of
TMN, the principles described below are very general and can be applied to
any management architecture.
Optical Network Management 311
The basis for the management of the optical network and its network
elements is the following simple rule:

The management of the optical layers must be separable from its client
layers, or, put another way the management of the optical layers is not
dependent on a particular client layer even if they are in the same box.
This rule is of fundamental importance; it ensures that the optical
network can support both existing and future, unforeseen, clients. It does
not necessarily mean that a link in an optical network simultaneously
supports a wide variety of clients, rather it suggests that regardless of which
protocol is supported in an instance of an optical network, the architecture
and management is the same as in all other instances of an optical network.
It allows WDM in a stand-alone platform connected to existing SDH
equipment to be managed in the same way as WDM and SDH integrated
within the same physical platform. This principle is also implicit in other
technologies such as ATM.
An optical management network (OMN) is defined as a subset of a TMN
that is responsible for managing optical network elements. An optical
network element, ONE, is that part of a network element that contains
entities from one or more OTN layer networks. According to this definition
the functions of an ONE may be contained in a stand-alone physical entity
(an equipment) that may or may not support other layer networks. Where
non-OTN layer network entities are in the same equipment they should be
considered as being administered separately from OTN entities. This
separation is a logical separation and it indicates that the management of
different technologies is not interdependent, and nor should it be. It does not
prevent them from both being available on a single element manager albeit
as separate applications.
312 OPTICAL WDM NETWORKS
Figure 7: Architecture of management networks
An OMN may be subdivided into a set of optical management
subnetworks, OMSNs (see Figure 7). In formal terms an OMSN can be
defined as a separate set of optical transport network embedded

communications channels and associated intrasite data communications
links which have been interconnected to form an operations data
communications control network within any given OTN transport topology.
In other words an OMSN represents a local communications portion of a
network. The entities contained within the OMSN and OMN are illustrated
in Figure 8. The operating system may be an element manager, a subnetwork
manager, or a network manager and there can be a hierarchy of such
systems.
Optical Network Management 313
Figure 8 Components of the management system
The concepts described above can be understood with reference to a
optically protected line system, similar to those being deployed in the BT
network, containing line terminals and optical line amplifiers, which is used
to interconnect SDH line terminals.
The optical line terminals and optical line amplifiers are managed within
a single OMSN. It should be noted that an OMSN might be applied to any
network topology, not just to optical line systems. The
SDH
terminals are
outside of the
OMSN
. Within the OMSN management communications is
by means of a messaging channel known as an embedded communications
channel (ECC) that is available to every network element. In the context of
G.872 it is generated and terminated on an OTS basis. This messaging
channel is only between ONEs. The
ECC
may be used to carry event
notifications and alarms from network elements or to convey
instructions/interrogations to the network element such as remote protection

switching requests or channel status. The ECC is carried within an optical
supervisory channel on a wavelength separate to all of the other optical
314 OPTICAL WDM NETWORKS
channels. It is inserted and extracted separately from the other optical
channels. For example in an optical line amplifier the optical supervisory
channel is extracted, converted to a digital signal, processed then reinserted,
whereas the other channels are amplified in the optical domain. A
supervisory channel also carries other information for the purposes of
operations administration and maintenance.
All of the network elements in the OMSN are managed by an operations
system, OS, (in this case it is an element manager). The OS is directly
connected to the two optical line terminals by means of a data
communications network. This network does not extend to the optical line
amplifiers. Instead the line terminals act as gateway network elements that
allow the OS to communicate with the line amplifiers by means of the
optical supervisory channel. The element manager is considered to be part
of the optical management network and can be used to manage optical
network elements in a number of OMSNs. Large networks will contain
many OMSNs and a number of element managers. Management
workstations are considered to be outside of the OMN but may be located
with the OS or remotely.
An example of a possible management hierarchy for managing optical
line systems is now considered. Optical line systems are in the lowest tier
and have access to the element managers via diverse data communications
links. If a data link or router is unavailable at one end of the line system the
system can be managed from the other end. The element managers (EM) are
located at a network administration and computing centre (NACC). This
allows the element managers to be maintained in central locations where
they can be maintained by specialized personnel.
The element managers are connected (again by way of diverse links) to

workstations at a remote network operations unit (NOU) which would be
responsible for managing not only the optical network but the SDH network
as well. Such a management network should be designed to meet the
following operational requirements:
– visibility of the optical network 24 hours a day, 365 days a year
– resilient network communications between workstations, element
managers and optical line systems to ensure availability even in the
event of management network failures
– provision of fallback facilities for the NOU
Optical Network Management 315
– management of the data-communication networks’ routers, links and
hubs
– provision of remote access facilities to allow supplier support under the
control of the operations personnel
– support of multiple user accounts wishing concurrent access
– visibility of multiple network elements simultaneously
– support of real time event handling and remote configuration
– allowance of management of optical line systems in the same way as
other technologies without the need for being an optical transmission
expert (It is essential that the personnel required to manage the optical
network elements are also skilled in managing multiple technologies. A
common approach to management is therefore required).
4. THE ROLE OF THE ELEMENT MANAGER
The element manager can be thought of as a go-between for the user
located at the workstation and the network element. Its role is to process
information for the purpose of monitoring/coordinating and/or controlling
network element functions. In TMN terms the relationship between the
managing entities and the managed entities is described by means of a
manager/agent relationship. A manager represents the managing process
whereas an agent represents the managed process, both of which are

software applications. In essence the manager software provides the
management functions and management services whereas the agent
applications provide access to the management information related to the
managed resources or managed objects described earlier. The
manager/agent model is hierarchical with the manager sending requests and
receiving replies. The operations system or element manager contains the
manager and the agent is contained within a network element. One manager
is normally associated with many agents. The element manager can be used
to retrieve information from network elements such as:
– network element id and location
– inventory, build number
– configuration
– current alarms or historical alarms from logs
– performance monitoring threshold levels
– active wavelengths, power levels, supported client signals, etc.
– ECC status
It can also be used to set information in the network element such as:
– initialization of network element
316 OPTICAL WDM NETWORKS
– optical protection state
– latching alarms, inhibiting alarm reporting
– initiation of 15 minute and 24 hour performance monitoring bins
– network element Id, Card Id etc.
– network element time
– single channel power levels and aggregate power levels
From the network element the element manager receives the following
– current alarms (these may be traffic or non-traffic affecting)
– threshold crossing alerts
– event notifications such as protection switching events,
insertion/removal of cards

– local logging, remote logging, user access information
The element manager also provides facilities such as security, in the
form of passwords and user profiles which determine the privileges of a
user, (read only, expert, administrator etc.), back-up facilities, network
element synchronization, and other administrative features.
5. FAULT MANAGEMENT IN STAND-ALONE SYSTEMS
A stand-alone optical line system is one that can be deployed without
having to modify the SDH systems connected to it. From the perspective of
the SDH systems the optical line system is “invisible” and can be considered
as virtual fiber. The network elements of the line system contain optical
layer network entities which are managed as part of an OMSN and layer
networks which are necessary for interworking with the legacy systems
(these layer network entities provide part of the functions of a transponder).
Although this interworking function within the line system, is not part of the
OMSN it is managed by the same element manager as the rest of the line
system. It should also be noted that different interworking functions
(transponders) could be used to support a variety of systems, not just SDH.
The layer networks of the SDH systems belong to a SDH management
subnetwork (SMS) and may be managed by a separate element manager.
Management communications is available between elements within the
optical line system and between the SDH systems but not between the line
systems and the SDH systems.
Optical Network Management 317
Where stand-alone systems are used, it is highly likely that operations
personnel will initially rely upon the element managers of the SDH systems
for identifying network problems. This is due to the size of the installed
SDH base. The number of SDH circuits is likely to be considerably larger
than the number of optical line systems, and personnel will not
automatically assume that a number of circuit failures occurring at the same
time correspond to failure of a multi-wavelength optical line system. The

natural assumption will be that there is a cable or SDH equipment failure.
Consider the case of a fiber failure that occurs within the optical line
system. This will result in downstream loss of signal that generates alarms
on the SDH network manager. Upon receipt of these alarms the SDH
manager will indicate the affected circuits and it will be assumed that there
is a multiple fiber failure within a duct. Upon checking network databases it
will become apparent that one or more of the underlying fibers supports a
WDM system. The operations personnel will then check the optical element
manager thereby determining the affected optical transmission section. If
the working route in the protected optical line system is affected, a loss of
line alarm and a protection switch notification will both be present.
Otherwise channel failures and possibly equipment failures are likely
causes. As a side note, if no alarms are detected on the optical element
manager then the fault can be assumed to be between the optical line system
and the SDH system receiver. Once the nature of a fault has been
determined and/or localized field personnel are dispatched to repair it under
the supervision of the NOU.
6. FAULT MANAGEMENT IN INTEGRATED SYSTEMS
The majority of optical line systems currently being deployed globally
are stand-alone systems that are being used to support legacy systems.
Where new build is being considered, there are a number of advantages to
integrating the optical transport layer networks into SDH equipment. The
principal advantage is the removal of optical transponders, which represent a
significant part of the cost of optical line systems. In this example every
network element is also an optical network element and the optical layers
are managed within an OMSN whereas the client layer network entities
within the end terminals are managed within a SMSN. Although these two
management subnetworks are logically separate they can be managed from a
single element manager. In contrast to the stand-alone case, management
communications is available between all of the network elements, and

network faults can be diagnosed in a single step manual process via a single
318 OPTICAL WDM NETWORKS
element manager. A further advantage is that the data communications
network structure is more straightforward than the stand-alone case.
7. MANAGEMENT OF OPTICAL RINGS
The management of optical line systems is relatively straightforward. In
addition to element managers the network operator should hold one or more
configuration databases that provide a record of the relationships between
the client circuits, the optical layers, fiber, cable and duct and the location
and type of optical network elements. In addition, for a network containing a
large number of optical line systems the operator may consider introducing
an interface between the optical element managers and a network level fault
manager for the purpose of fault correlation across technologies and
identifying the root cause of the fault. This will also minimize the number of
alarms that have to be processed by the user.
Optical rings, although only slightly more complex than optical line
systems, require far more network management capabilities to be provided
by the supplier. The major difference is that the optical channel is now
reconfigurable. In addition to simple element management, it is a
requirement that the optical connections between network elements are
visible. This requires some level of network management of links, trails and
subnetwork connections. This ability to reconfigure means that it is no
longer acceptable to have a configuration database recording a static
relationship between an optical channel and its server layers. Manual
updating of this relationship is not reliable and it will not be possible to keep
up with configuration changes due, for example, to protection switching. In
case of a discrepancy, which is correct the entry in the database or the
connection in the network? For this reason it is better to automate the
configuration process and ensure synchronization with the network by
means of an application programming interface between the database and

the element managers:
The network management system for a ring also requires the following
capabilities
– an electronic interface between the element managers and the
subnetwork manager to allow event messages to be passed to the subnet
manager for surveillance and configuration messages to be passed to the
element managers
– capability of detecting and notifying mis-connections. The optical
channel overhead provides such a capability by means of a trail trace,
Optical Network Management
319
which compares the incoming label with the expected label. Trail trace
is not required at the optical channel level in an optical line system, but
is in any system where optical channels can be reconfigured
– ability to suppress alarms that are associated with configuration changes
and filtering to reduce consequential alarms
– indication of circuit status, e.g. reserved, in-service, failed routings, etc.
– support for monitoring repair work and to provide a log of repair
activities until the fault is resolved
– support for concurrent users involved in planning, configuration,
surveillance and repair
– planning tools. In contrast to digital networks 3R regeneration is not
available in every network element for every channel. Therefore, when
designing the network it will be necessary to measure fiber parameters
such as loss and polarization mode dispersion to calculate if the network
elements can be placed in the desired locations and that any and all
paths can be configured within the ring for both working and protection
modes. It is not acceptable to put the equipment into the ground and
then discover it will not work when an attempt is made to set-up the first
or indeed the last circuit. This represents a major challenge for optical

networking. The greater the number of optical network elements the
greater the problem. This indicates why the digital wrapper is likely to
be more successful than any all-optical counterpart.
As the number of optical rings increases the operator will eventually
want to interconnect traffic between them. There are essentially two ways in
which this can be achieved. The simplest is to manually connect a tributary
from an OADM in one ring to a tributary on an OADM in another ring. The
result of traffic churn is that such a connection may need to be altered many
times. For some network operators this may not be seen as a problem,
particularly if it is a small network. However, for larger operators there is
considerable operational saving to be made by providing automatic
provisioning. This can be achieved by means of an optical cross-connect
between the rings.
How does the network operator set up such a connection automatically?
Again there are two ways. The first is that personnel in the network
management centre plan the route using a network database and then
remotely configure a connection through each network element (having to
set up each network element separately) in the end-to-end path. This is time
consuming, laborious and prone to error. If the supplier provides only
element management, the network operator may have no other choice.
However, the number of circuits that need to be set-up and torn down each
day will increase with network size, and this method will not scale.
320 OPTICAL WDM NETWORKS
The second way is to provide auto-routing capabilities. This requires a
network database that contains a model of the network, including not only
the equipment contained within it but also the connectivity of all of the links
and subnetworks in each of the layer networks. It is important to reiterate
that the information stored in this configuration database should be obtained
from the network (via the management interfaces to the network elements)
and not from manually keying it in. This ensures that the database reflects

what is in the network. Auto-routing tools would use this database to
calculate the appropriate path through the network, based on algorithms and
planning rules. Once the path is determined the network management system
provides configuration commands to the network elements. Such an
approach allows large numbers of circuits to be configured per day. Instead
of drilling down into each network element one after the other, the user need
now only specify the two end points. Whereas some network operators
currently have such a capability for SDH and can configure the network
with a small number of people it is of little use if the underlying optical
layer still requires manual configuration between its subnetworks and its
connections to the SDH network. Unfortunately this may be the case for
some time to come.
At the present time nearly all optical network management is based upon
element managers, and first generation subnetwork managers are likely to
manage small subnetworks such as rings. These may be provided by
suppliers or built by the network operator. If we assume the former it is
obvious that if there is more than one supplier in the network it will be
necessary to provide a network manager that can manage both subnetworks
and set-up connections across them. At this point it should be obvious that
we are now talking about very large systems and the major problems are
volumetrics and scalability.
8. MANAGING INTERCONNECT
Up until now the discussion has focussed on network management within
a single administrative domain but there will also be a need to network
optical channels between administrative domains. There are some
differences between inter- and intra-domain network management, and these
can be understood by means of reference to a simple interconnect regime –
an optical line system connecting two operators. Such an environment is
likely to be controlled by national or regional regulators. A consequence of
this is that interconnection will probably be across a transversely compatible

Optical Network Management 321
interface that allows network operators to have different vendors equipment
at each end. The boundary between operators in this system can be
considered as an accessible point on a fiber (e.g., via a footway box), known
as the point of interconnection (POI). The optical channel link connection
between administrative domains will be regenerated at both ends (to ensure
that the ingress and egress signals are of the highest possible quality) and
tandem connection monitoring will be employed. However, no network
management information will be transferred between network operators
using the embedded communications channel. This is unsurprising; network
operators are unlikely, except by mutual consent, to allow other operators
management access to their network. Instead the operators will rely on a
single ended-maintenance strategy that allows management of the network
element within their own administrative domain and the use of defect
indicators to detect a far end problem in the other operators domain. Where
problems are identified on the fiber, each operator will dispatch
maintenance personnel to test each end of the link and identify which side of
the POI it occurs. Manual processes are therefore required between the
operators in order to co-ordinate the management of this link. A similar
management strategy can be envisaged for international links.
9. SUMMARY
This chapter has provided a brief overview of the network management
domain. It should be recognized that optical networks will be extremely
difficult to operate without large scale management systems. The current
trend of providing hardware products well in advance of systems that can
manage them constitutes a major threat to successful widespread
deployment.
References
1. ITU-T Recommendation G.805, “Generic Functional Architecture of
Transport Networks.”

2. ITU-T Recommendation G.872, “Architecture of Optical Transport
Networks.”
3. ITU-T Recommendation G.957, “Optical Interfaces for Equipment and
Systems Relating to the Synchronous Digital Hierarchy.”
4. ITU-T Recommendation M.3010, “Principles for a Telecommunications
Management Network.”