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- Networks and Telecommunications: Design and Operation, Second Edition.
Martin P. Clark
Copyright © 1991, 1997 John Wiley & Sons Ltd
ISBNs: 0-471-97346-7 (Hardback); 0-470-84158-3 (Electronic)
PART 5
RUNNING A
NETWORK
- Networks and Telecommunications: Design and Operation, Second Edition.
Martin P. Clark
Copyright © 1991, 1997 John Wiley & Sons Ltd
ISBNs: 0-471-97346-7 (Hardback); 0-470-84158-3 (Electronic)
27
Telecommunications Management
Network (TMN)
The goalof the ‘telecommunications management network’o r ‘ T M Nis to provide for consistent
and efficient management of complex telecommunications networks. The T M N model describes
the basic operating and management functionswhich a network operator has to conduct and the
standard interfaces to be used between network components and network managementsystems.
Key elements of the T M N concept are the management model, the Q3-interface and the CMIP
(commonmanagementinformationprotocol).We discuss them allinthis chapter, whichin
parallel gives an insight into the problems of managing complex networks. At the end, we also
briefly discuss the SNMP (simple network management protocol), which is used as analternative
to CMIP in many corporate and Internet/router networks.
27.1 THE PROBLEMS OF MANAGING NETWORKS
Figure 27.1 illustrates a typical telecommunications network of today. It provides a
valuable insight into the complexity of managing even relatively simple telecommunica-
tions networks. The figure shows a simple data network composed of four different
component types, buteachprovided by different manufacturers.Theyeachhave
independent network management systems ( N M S ) . Each NMS is capable of monitoring
and controlling every aspect its manufacturer’s network equipment, but is incapable of
monitoring or controlling other manufacturers’ devices. The componenttypes shown are
0 data switches, managed by a ‘proprietary’ network management system, NMSl
0 SDH (synchronousdigitalhierarchy)transmissiontechnology(linkssome of the
switches and is managed by NMS2)
0 TDM (time division multiplex) transmission technology (links some of the switches
and is managed by NMS3)
477
- 478 (TMN) NETWORK
TELECOMMUNICATIONS
MANAGEMENT
0 direct leaselines provide for remaining switch links. These are supplied by another,
public telecommunications network operator, for which there is no management
system available to our operator
A simple line failure is illustrated in Figure 27.1. An SDH connection has failed. The
result is a plethora of alarms generated by both NMSl andNMS2. The network status
screens of both NMS are likely to light up like Christmas trees in all sorts of colours.
The SDH network management system, NMS2, will pinpoint the root cause of the
problem, probably with the appropriate link alarm indicated in red. Meanwhile, NMSl
is also showing red alarms, because one the adjoining switches has a malfunctioning
of
port and the other adjoining switch is isolated.Otherswitchesmayreport ‘yellow
alarms’ as connections to the isolated switch have been lost. The exact cause of the
problem, however, will not be clear from the information that appears on NMS1. Un-
fortunately, this is likely to lead to a certain amountof confusion and wasted effort.. .
. . .The human operator managing the SDH network naturally starts about his
repair. . .meanwhile. . .
. ..His colleague, the switch network manager watching the screen of NMSl is
unaware of the root cause. Instead he addresses what appears to him to be the urgent
problem of the isolated switch. Perhaps there has been a power failure? Maybe the
switch needs to be restarted?.. .He calls his colleagueat the isolatedswitch site. Having
done so, he is able to rule out a local cause. next he calls his SDH colleague and, of
So
course, discovers the most likely cause of his own alarms. He hands over responsibility
and starts to get on with something else.
But, you might ask, why did the switch manager not call the SDH manager to start
with? The answer is that he is unable to determine easily the single cause of a lot of
alarms. He must therefore address each alarm in turn, diagnosing the most critical
alarms first.
Considerable effort may go into checking each alarm and concluding a single root
cause. Only afterwards can the human network manager truly rest in peacehis SDH as
Q alarm $( line failure
Figure 27.1 A typical telecommunications network
- NETWORK PROVISIONING 479
Figure 27.2 Recognizingthatanetwork islikespaghettiandthealarms are like Christmas
tree lights
colleague gets on with the job of network restoration. Afterwards, despite his clear
conscience, the alarms on his own screen do not go away.. . So when another fault
arises before the first is cleared, the diagnosis becomes more confused and difficult as
the alarms inter-mingle.
In real networks, many simultaneous faults are likely to be present at any point in
time, even if they are of a non-critical nature. Working out which alarm belongs to
which bit of network equipment is a complex task, like finding the knot in spaghetti!
(Figure 27.2).
27.2 NETWORK PROVISIONING
Provisioning of new lines in the network just as complex and labour-intensive as fault
is
finding. Imagine trying to up a single permanent connection (say a frame relay PVC)
set
across the networks of either Figure 27.1 or Figure 27.2. First someone must sit down
to ‘design’ the connection (work out the path), allocate ports and network addresses.
Next, each of the TDM and telephone switch ports need to be programmed. The SDH
links must be configured. The leaselines must be ordered. Finally comes the hope that
all the installation staff in the chain do their jobs on-time and accurately, otherwise
the connection fails an end-to-end acceptance check. It would be preferable to define
the desired end-points of the connectionand let a computer coordinate and execute the
rest. Enormous savingineffort is possible,togetherwithhigherquality and faster
installation work.
. . . And by being able quickly to trace the complete path or trailof a single connec-
tionthroughthenetwork (e.g. Figure 27.2) usingsophisticatedcomputernetwork
managementtools,operationsstaffcanmorequicklydiagnosefaultsandresolve
- 480 TELECOMMUNICATIONS MANAGEMENT NETWORK (TMN)
problems if they arise later. Furthermore, by computer ‘filtering’ of the alarms, it may
be possibleto reduce the ‘Christmas tree lights’ the one or two alarms are most
to which
likely to be the direct cause of a problem. This would greatly help our fault-correcting
friends in Figure 27.1.
27.3 UMBRELLA NETWORK MANAGEMENTSYSTEMS
A number of network operators, computer manufacturers and software developers
started during the 1980s to develop the idea of umbrella network management systems
(Figure 27.3). These were to be powerful network management systems capable of
controlling the network as a whole. They would be able to correlate and present the
various pieces of information from individual network element managers ( N E M ) thus
removing this arduous coordination task from human operators. (Note: NMS1, NMS2
and NMS3 of Figure 27.1 are network element managers because they are network
management systems capable only of managing a particular typeof network element.)
A single command issued to the umbrella systemby a human operator would be all
that is needed to configure a new trunk between any two of the switches Figure 27.1.
of
The umbrella system managers see to it that the plethora of comands needed to be
issued to the individual network elements are generated (one command to configure a
new port at one switch, a second command for the second switch, a third command to
the SDH NMS to establish the transmission path, etc.).
For the umbrella network management system to work properly, a defined, standard
interface between the umbrella network management system and each of the network
element managers is needed. Over this interface the umbrella network management
umbrella network
management system
- NETWORK UMBRELLA MANAGEMENT SYSTEMS 481
system needs to be capable of receiving information on request about the status of
specific network elements and to be able to issue commands for reconfiguration or
control of the various sub-networks.
One of the first steps taken by CCITT (now ITU-T) in defining its standards for
telecommunications management network ( T M N ) was to define a model of the various
functions and interfaces going to make up a complete network management system.
This is laid out in ITU-T recommendation M.3010 and is illustrated in Figure 27.4.
The key components of the TMN model (Figure 27.4) are the operating system ( O S ) ,
the network element (actually the network element manager) and the workstation ( W S ) .
The key interfaces are the Q3-interface, the X-interface and the F-interface. The data
communicationsnetwork ( D C N ) merelyprovidesameans for connectingtogether
network management devices and network components in different locations.
The operating system ( O S ) is analogous to what we previously called an umbrella
network management system,except that there is no longer any presumption that all the
variousnetwork operations, administration and management functions pro-
(e.g.
visioning, troubleshooting, etc.) can be handled by a single computer system. Instead,
a number of operating systems combined together will handle the full functionality of
our previous umbrella system. A standard interface between operatingsystems(the
X-interface) allows this subdivision.
Individual network elements ( N E ) probably each have their own proprietary network
management systems (network element managers), which cater for the specialized func-
tions and operating methodsof a particular manufacturers hardware. The Q3-interface
provides for a standard means of communication between the operating systems (i.e.
‘umbrella’ managers) and individual NEMs. The network element manager acts as an
m
DCN data communications network
F-interface interface OS to WS
MD mediation device
NE network element
os operations system
(&-interface interface of TMN to NE
QA Q adaptor
ws workstation
X-interface interface between TMNs
Figure 27.4 TMN model: defined functions and interfaces (courtesy o f ITU-T)
- 482 (TMN) TELECOMMUNICATIONS
NETWORK
MANAGEMENT
network manaaer
l
Figure 27.5 4 3 - and X-interfacesaretheimportantinterfacesbetweennetworkmanagers
and agents
agent, interpreting the commands issued across the Q3-interface and reacting upon them
in conjunction with the individual network elements. Thus status information can sent
be
to the manager and control commands can be executed in the network by the agent.
When necessary, a translation function can be used to convert Q3-interface com-
mands into the proprietary format needed by a specific network element. This trans-
lation function is termed the Q-adaptor function ( Q A ) . Where the individual network
elements can respond directly to Q3 commands, it is not necessary.
The term mediationdevice is applied to anydevicecarrying out a conversion of
protocol or data format necessary for the interconnection of devices. The diagram
should not be taken to imply that a single mediation device will cater for all necessary
mediation needs.
The work station ( W S ) is equivalent to a technicians laptop computer. A standard
interface(the F-interface) allows him to log intothe manager(operatingsystem)
wherever he may be (in the exchange building or in the field).
Figure 27.5 duplicates the TMN model as already shown in Figure 27.4, but now we
see more clearly the typical system boundaries of real network management systems.
The manager is a so-called umbrella network management system, capable of consoli-
dating information fed to it by separate proprietary network element managers ( N E M ) .
The manager communicates with the various individual network element managers by
means of the Q3-interface, interpreting the standardized 4 enquiries and commands
3
and translating them as necessary into the proprietary formatof the particular network
component.
- THE Q3-INTERFACE 483
27.4 THE Q3-INTERFACE, THECOMMON MANAGEMENT
INFORMATION PROTOCOL(CMIP)ANDTHE CONCEPT OF
MANAGED OBLECTS (MO)
Crucial the
for successful
communication
between
manager agent the
and over
Q3-interface are
0 the definition of a standard protocol (set of rules) for communication (this is the
common management information protocol, C M I P )
0 the definition of standardized network status information and control messages for
particular standardized types of network components (so-called managed objects)
C M I P (common management information protocol) delivers the common management
information service ( C M I S ) to the operating system of Figure 21.4. CMIS is the service
allowinga CMISE (common managementinformationservice entity, i.e.asoftware
function)inthemanager to communicatestatusinformationandnetworkcontrol
commands with a CMISE in each of the various agents. CMIP itself is an OS1 layer 7
protocol, which sets out the rules by which the information and commands (CMISE
services) may be conveyed from manager to agent or vice-versa. These basic CMISE
services are restricted in number. They are listed in Table 27.1.
However,alone, CMISandCMIPdonot conveyanyusefulinformation from
manager to agent. They are simply the ‘rules orderly conversation’. In the same way
of
that theproject manager of a major building projectcan make sure that instructions are
Table 27.1 The basic CMISE (common management information service entity) services
Service name Function
M-ACTION service
This requests an action to be
performed on managed
a object,
defining conditional
any statementswhich be
must fulfilled
before
committing to action
M-CANCEL-GETThisserviceisused to requestcancellationof an outstandingpreviously
requested M-GET command
M-CREATE service
This is used to create new instance of a
a managed
object
(e.g. a
new port now being installed)
M-DELETE service used
This is to delete an instance of amanagedobject a
(e.g. port
being taken out of service)
M-EVENT-REPORT This service reports an event, including managed object type, event type,
event time, event information, event reply and any errors
M-GET requests
This
service status
information values)
(attributeaof
given
managed object. Certain filters may be set limit the scope of the reply
to
M-SET requests
This
service modification
the of a managedattribute
object
value (i.e. is a command for parameter reconfiguration)
- 484 (TMN) NETWORK
TELECOMMUNICATIONS
MANAGEMENT
issued to the electrician, the brick layer and the plumber and thateach of the craftsmen
understands his instructions and completes them on time, so CMIS is able to ‘project
manage’ the task of managing a network. The actual content of the network manage-
ment ‘work instructions’ depends on the particular network component being managed,
and is codedaccording totheappropriate managementinformationbase ( M Z B ) of
managed objects.
A managedobject isastandardizeddefinitionofaparticulartype of network
component, and thenormalized states in which it can exist. Imagining a water bottle to
be described as a standard managed object it might be ‘a vessel for storing one litre of
liquid’ (exactly what shape itis, is unimportant). Its top might be a screw top, a cap-top
or a cork, but as a managed object all three are simply ‘watertight stoppers’ which may
either be ‘secured’ or ‘opened’. Standardized states may thus be ‘full’, ‘empty’, ‘half
full’, etc., while control commands might be ‘fill up’, ‘pour out’, ‘secure stopper’, ‘undo
stopper’, etc. Provided that all manufacturers of water bottles produced products able
to respond to these commands you can buywhichever device is mostaesthetically
pleasing without the concern of not being able to get the lid off!
Managed objects are nowadays defined for most new computer and telecommunica-
tions products. They may be defined either on an industry standard basis or by the
individual manufacturer, where industry standards not
do exist. They usually grouped
are
into sets corresponding to individual device types or network components. These are
called management information bases (MZBs). Thus there is an MZB for routers used
on the Internet. There is also an MZB for the ISDN basic rate interface (Chapter 10).
Of course there are many other MIBs, but many more will need to be defined.
Having well-defined MIBs for each of the network componentsis key the realization
of the dream of a complete umbrella manager, capable of coordinating all network
components. It is thus the MIBs which provide the critical information content of the
messages. It is, after all, of no use to tell someone to ‘act on’ or ‘carry out’ something
unless you also tell him you are talking about the ‘water bottle’ and he is to ‘open it’).
address profile
businessuser teleservice
viceAccessPoint residentialuser
Figure 27.6 A simple managed object inheritance hierarchy
- MODELTHE I S 0 MANAGEMENT 485
The definition of managed objects ( M O ) and managed information bases (MIBs),
like other OS1 layer 7 protocol objects, is carried out in the abstract syntax notation 1
( A S N . 1 ) about which we learned in Chapter 9. The procedure of definition, including
advice on how to group and subdivide MOs is definedin ITU-Trecommendation
X.722. These are the guidelines f o r the dejinition of managed objects (GDMO). They
includestrictrules about the naming and spelling conventions and the hierarchical
structure.
There are a number of commercial software products availableto help with the task
(so-called GDMO browsers). Figure 27.6 illustrates a relatively simple managed object
inheritancehierarchy, showing the various states and attributes of a given managed
object (in this case a network service).
27.5 THE I S 0 MANAGEMENT MODEL
I S 0 (International Organization for Standardization) has developed a standard model
classifying the functional processes which must be undertaken in the management of
computer and telecommunications networks. All management tasks are classified into
one of the following five (FCAPS) categories
0 Fault management
0 Configuration
management
0 Accounting
management
0 Performancemanagement,and
0 Security
management
This model is referred to widely by ITU-T’s recommendations on a telecommunications
management network, and is reproduced in the ITU-T X.700-series recommendations.
Fault management is the logging of reported problems, the diagnosis of both short
and long term problems, ‘blackspot’ analysis and the correction of faults.
Conjigurationmanagement is themaintenance of networktopologyinformation,
routing tables, numbering, addressingand other network documentation and the coord-
ianation of network configuration changes.
Accounting management is the collection and processing of network usage informa-
tion as necessary for the correct billing and invoicing of customers and the settlement
with operators of interconnected networks.
Performance management is the job of managing the traffic flows in a live network,
monitoring the traffic flows on individual links against critical threshold values and
extending the capacity of links or changing the topology by adding new links. It is the
task of ensuring performance meets design objective (e.g. service level agreement).
Security management functions include
0 identification, validation and authorization of network users andTMN system users
0 security of data
- 486 (TMN) TELECOMMUNICATIONS
NETWORK
MANAGEMENT
0 confirmation of requestednetworkmanagementactions,particularlycommands
creating or likely to create major network or service upheaval
0 logging of network management actions (forrecovery purposes when necessary, and
also for fault auditing)
0 maintenance of data consistency using strict change management
27.6 TMNMANAGEMENTFUNCTION MODEL
Figure 27.7 illustrates the five layers of functionality defined by the OS1 management
model for a TMN. The layers are intended to help in the clear and rational definition of
TMN operating system boundaries, so simplifying the definition, design and realisation
of systems, by simplifying their data and communication relationships to one another.
At the lowest functional layer of Figure 27.7 (network element layer, N E L ) are the
networkelements themselves.These are the active components making up the net-
works. Above them, in the second layer of the hierarchy, is the element management
layer ( E M L ) containing element managers. Element managers are devices which control
single network components or sub-networks (e.g. a local management terminal or a
proprietary network management system).
At the third layer, the network management layer ( N M L ) are managers which control
the main aspects of a given network type (e.g. ISDN or ATM).
management 1
layer
management
layer
management
layer
management
layer
element
layer
Figure 2 . The functional layers of TMN
77
- THE NETWORK
MANAGEMENT
FORUM
(NMF),
OMNIPOINT AND SPIRIT 487
The service management layer ( S M L ) contains service managers which monitor and
control allaspectsofa given service, onanetwork indepdndentbasis.Thus, for
example, it is possible in theory to conceive a frame relay service provided over three
different network types: packet switched-type network, ISDN and ATM. The service
manager ensures installation a
of given customersconnection line needs onthe
appropriate network(s) and monitors the service delivered against a contracted frame
relay service level agreement.
The business management layer ( B M L )contains functionality necessary for the man-
agement of a network operator’s company organization as a whole. Thus purchasing,
or
bookkeeping and executive reporting and information systems are all resident in this
layer.
27.7 THE NETWORK MANAGEMENT FORUM (NMF),
OMNIPOINT AND SPIRIT
In addition to the standardization activities of IS0 and ITU-T, a number of industry
initiativeshave been commencedoverthelast six years to speedprogressinthe
development of umbrella network management systems.
The firstmajorinitiative,startedin 1989, wasthe NetworkManagementForum
( N M F ) . This is composed of major network operators (e.g. British Telecom) and com-
puter manufacturers (e.g. IBM, DEC, SUN, Hewlett Packard), who have together formed
a common interest group to speed the realization and acceptance of common network
management standards. Valuable outputs of this group have been the OMNIpoint and
SPIRIT specifications.
The OMNIpoint specifications are intended as a set of specifications and guidelines
for implementors of network management systems. They attempt to review standards
issued by main standards bodies and build inputs from various sources into a con-
solidated (and realisable) whole. Where standards are vague, N M F in its OMNIpoint
specifications aims to provide further clarifying specifications.
A number of hardware and software manufacturers claim alreadyto have OMNIpoint-
compliantsystems.These,inthemain,aresystemscompliantwith OMNIpointl.
Unfortunately, compliance to OMNIpointl not mean much. Compatibility com-
does of
pliant systems is not guaranteed. More interesting is OMNIpoint2, which has recently
(November 1995) been published by NMF. This aims to be a fuller set of specifications
for TMN-compliant systems.
A second valuable output of N M F has been the SPIRIT (service providers integrated
requirements f o r informationtechnology) specifications.These attempt to lay out a
standard hardware and computer operating system software platform for the realiza-
tion of development and run-time platforms for TMN-compliant network management
systems. SPIRIT 2.0 was issued in November 1994.
27.8 REALIZATION OF ATMN
How does this
all fit together?
Figure 27.8 shows a
possible
layered
software
configuration of a TMN system, based on a client/server computer hardware platform
- 488 (TMN) TELECOMMUNICATIONS
NETWORK
MANAGEMENT
TMN applications
TMN platform
components and software
development
platform
and test
ORB (CORBA) environment
computer
hardware and
operating system
software
{7 11
data network
ORB = object request broker
CORBA = common object request broker architecture
NE = network element
Figure 27.8 Possible computer hardware and software realization of TMN
according to SPIRIT, with the latest object-oriented computing software (CORBA)
loaded upon it. Above this, there are some generic tools and processes, thereby limiting
theamount of software which hasto be writtenfor specific services or network
operators. The layered approach leads to more rapid development, greater sharing
with
of development costs and benefits.
27.9 EXAMPLE OF EARLY TMN REALIZATION
The operations and maintenance functions defined for ATM networks are designed
according to the principles of the telecommunicationsmanagement network ( T M N ) .
Specifically, the ATM standards define the following management functions
0 performance
monitoring
0 defect and failure detection (by continuous monitoring and generation of alarms)
0 networkand systemreconfiguration(includingautomaticchangeovertobackup
facilities)
0 fault
localization
- NETWORK
SIMPLE MANAGEMENT PROTOCOL
(SNMP) 489
In addition to TMNinterfaces, some earlyATM equipment is likely to offer the S N M P
(simple network management protocol), because this is the basis of the ATM interim
local management interface ( I L M I ) . ILMI enables the management of UN1 managed
objects (switches, devices, parameter settings, etc.),
thus making management control of
devices possible across the ATM UNI. Together the managed objects make up the UN1
management information base ( M I B ) .
The short term attraction of SNMP as the basis for ILMI lies in its widespread
deployment in existing corporate data networks, routers, LANs (local area networks)
and Internet components.
Future standardization work on ATMnetwork management is likely to concentrate
on migration to the CMZP protocol (probably by integration of certain SNMP pro-
cedures into it). In addition, a huge amount work must be applied to the definition of
of
the standard M I B (management information base) of managed objects relevant to ATM
networks and devices. Without these definitions, it will be impossible to develop the
necessary tools for management of the network as a whole. At the moment these are
poorly defined.
27.10 SIMPLE NETWORK MANAGEMENT PROTOCOL (SNMP)
The simple network management protocol( S N M P ) is a protocol in many ways similar to
TMN’s common management information protocol ( C M I P ) . It also allows for creation
of umbrella network management systems by allowing for communication of status
information and commands (i.e. management information base, M I B information) by
means of an industry-wide accepted protocol. The main technical difference between
SNMP and CMIP is its simplicity. SNMP was developed by the Internet Engineering
Task Force ( I E T F ) and is defined in its specification RFC 1157.
Although ITU-T was developing CMIP asa robust protocol, conforming with all the
requirements of the OS1 model, the engineers involved in developing and installing
routers and other networks for the Internet and other corporate data networks were
keen to have a short term solution. SNMP was the answer. It is widely deployed in
corporate data networks, where the term S N M P manager is applied to several types of
available devices capable of acting as basic umbrella network managers.
A new version of SNMP, SNMP2 has recently been agreed. This is significantly more
complex than SNMP. Meanwhile, SNMP and CMIP protocols are beginning to con-
verge as the work on defining common management information bases proceeds.
27.11 SUMMARYOFTMN BENEFITS
Assimilation of the various functions and interfaces of the TMN architecture into the
network management plans network operating organizations has a number
of of benefits
0 the
opportunityto develop quality
high networkmanagement
methods and
processes supported by industry-standard products
- 490 (TMN) TELECOMMUNICATIONS
NETWORK
MANAGEMENT
0 the scope to force suppliers of network switches and other components to develop
new functionality crucial to effective network management and TMN as a whole
0 in particular, Q3-interface CMIP
the and (common management
information
protocol) are already widely adopted standards
27.12 TELECOMMUNICATIONS INTELLIGENT NETWORK
ARCHITECTURE (TINA)
Finally,the telecommunicationsintelligentnetworkarchitecture (TINA ) should be
mentioned before leaving the subject of TMN, because there are some areasof overlap.
TINA is a relatively new initiative, based upon the observation that both intelligent
networks (Chapter 11) and T M N areaddressingtheproblems of management of
complex networks. TZNA is an attempt to combineTMN and intelligent network ideas
and to re-define the ideal network architecture of future networks.
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