GB2433678A

GB2433678A - Alarm condition detection in a cellular communication system

Info

Publication number: GB2433678A
Application number: GB0525434A
Authority: GB
Inventors: Javier Lopez Fernandez
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2005-12-14
Filing date: 2005-12-14
Publication date: 2007-06-27
Anticipated expiration: 2025-12-14
Also published as: GB0525434D0; GB2433678B

Abstract

An alarm condition detection apparatus (107) for a cellular communication system comprises a monitoring processor (201) which monitors the input and output of a network element of the cellular communication system. The alarm condition detection apparatus (107) also comprises a model processor (209) which determines an expected output from the network element in response to a monitored input to the network element by evaluating a model of the network element for the monitored input. The model may be a simple association between predefined input messages and expected output messages arising from these input messages. An alarm generator (211) is arranged to generate an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element. The alarm condition detection apparatus (107) may be hardware and software segregated from the associated network element.

Description

ALARN CONDITION DETECTION IN A CELLULAR COMMUNICATION SYSTEM

Field of the invention

The invention relates to alarm condition detection in a cellular communication system and in particular, but not exclusively, to alarm generation in a Global System for Mobile communication (GSM) or Universal Mobile Telecommunication System (UMTS) communication system.

Background of the Invention

Currently, the most ubiquitous cellular communication system is the 2nd generation communication system known as the Global System for Mobile communication (GSM). Further description of the GSM TDMA communication system can be found in The GSM System for Mobile Communications' by Michel Mouly and Marie Bernadette Pautet, Bay Foreign * Language Books, 1992, ISBN 2950719007.

3rd generation systems have recently been rolled out in many areas to further enhance the communication services provided to mobile users. One such system is the Universal Mobile Telecommunication System (UMTS), which is currently being deployed. Further description of CDMA and specifically of the Wideband CDMA (WCDMA) mode of UMTS can be found in WCDMA for UNTS', Harri Holma (editor), Antti Toskala (Editor), Wiley & Sons, 2001, ISBN 0471486876. The core network of UMTS is built on the use of SGSN5 and GGSNs thereby providing commonality with GPRS.

Current telecommunication networks are very complex systems comprising large numbers of different types of network elements. In order to ensure high reliability and an efficient operation of the cellular communication system, it is necessary to monitor the operational state of the individual network elements. For example, it is important to detect, identify and localise fault conditions in a cellular communication system.

Early telecommunication networks were based on specific hardware performing narrowly defined functions. Component failures where easily detected and the failing network element could easily be determined leading to a relatively easy and quick diagnostic process. * ** * I S p... S...

However, the evolution of telecommunication networks have lead to increasingly complex systems wherein network

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* S elements are increasingly based on software implemented functionality using general purpose hardware. Furthermore, : the advances in hardware and software technology have * allowed system designers to substantially increase the S.....

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complexity and variety of functionality provided. This has resulted in a significant increase in for example the number of features, the complexity and size of the software and the interactions between components. However, although these advances allow improved and increased functionality it has also resulted in an increased risk of faults and especially software errors as well as more complex fault conditions and effects.

In order to increase the reliability of a cellular communication system, many network elements comprise internal means for detecting fault conditions and for raising an alarm if a fault condition occurs. However, such an approach tends to be suboptimal.

For example, it is typically very difficult to localise sources of faults in such systems as the detected error condition can result from a number of different sources and it is not uncommon for a single fault to result in alarms being raised by a number of different network elements. For example, if an error occurs in a check sum, all network elements verifying this check sum will raise an alarm even if they did not cause the fault.

:.:::. Furthermore, the approach is relatively inflexible as it **s$ requires the functionality to be built into the network device thereby making modifications and updates more *SOS. * *

difficult to achieve.

*::: : Also, as the alarm systems are integrated with the network elements themselves, there is no completely independent verification of the operation of the network element. For example, during the design stage the same error can be built into both the operating and the check functionality as they share the same design process (e.g. the same erroneous assumption or oversight can be applied to both systems).

Furthermore, as the same hardware and/or software platforms are used, common errors may occur. Specifically, unfortunate event sequences or transitions may cause faults in both the operating and the check functionality which can lead to e.g. faults not being reported or being reported when no faults occur.

Hence, an improved system would be advantageous and in particular a system allowing increased flexibility, reduced complexity, increased reliability, facilitated alarm/ fault localisation and/or improved alarm detection performance

Summary of the Invention

Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination. * *. * * S 555* S...

According to a first aspect of the invention, there is provided an alarm condition detection apparatus for a I.....

* cellular communication system, the apparatus comprising: monitoring means for monitoring the input and output of at *: * least one network element of the cellular communication

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*....: system; model means for determining an expected output from the network element in response to a monitored input to the network element by evaluating a model of the network element for the monitored input; and alarm means for generating an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element.

The invention may allow improved alarm condition detection in a cellular communication system. In particular, an improved segregation between network element and alarm generation functionality can be achieved resulting in improved reliability and accuracy of the alarm generation.

The alarm condition detection apparatus can be completely separate from the network element and can be designed, manufactured and/or developed independently of the network element. The model of the network element may be a lower complexity model resulting in a low complexity alarm condition detection apparatus which may be low cost and/or easy to implement and/or to introduce to a cellular communication system. A facilitated and/or improved localisation station of the source of the alarm may be provided.

The alarm generation may specifically be of a fault alarm which is indicative of a fault being detected in the network **** element. IS.. S * *S*

According to an optional feature of the invention, the alarm S.... * .

condition detection apparatus has a management network connection which is independent of management network * connections of the at least one network element.

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SI*e. * S

This may allow improved segregation between the network elements and the alarm condition detection apparatus and/or may increase the reliability and/or accuracy of the alarm generation.

According to an optional feature of the invention, software of the alarm condition detection apparatus is segregated from software of the at least one network element.

This may increase the reliability and/or accuracy of the alarm generation. The segregation may be such that there is no interaction or shared resource between software of the alarm condition detection apparatus and software of the at least one network element except for the input and output communication between the network element and other network elements of the cellular communication system.

According to an optional feature of the invention, hardware of the alarm condition detection apparatus is segregated from hardware of the at least one network element.

This may increase the reliability and/or accuracy of the alarm generation. The segregation may be such that there is no interaction or shared resource between hardware of the * .* * * S alarm condition detection apparatus and hardware of the at *S.*

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least one network element.

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*S*I.* * S According to an optional feature of the invention, the alarm condition detection apparatus has an independent power * source from the at least one network element.

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This may increase the reliability and/or accuracy of the alarm generation.

According to an optional feature of the invention, the alarm condition detection apparatus is uniquely associated with a group of network elements comprising the at least one network element.

This may provide facilitated and/or improved localisation of the source of the generated alarm and may specifically in the case of a fault alarm allow an improved identification and/or localisation of the fault.

According to an optional feature of the invention, the alarm means is arranged to generate an alarm only if an invalid output from the at least one network element is detected for a valid input to the at least one network element.

This may allow an improved alarm generation and may specifically allow a low complexity yet efficient implementation. Specifically, the feature may facilitate alarm source localisation and may prevent alarms being generated in response to a fault occurring in another network element * *5

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The determination of the valid input may be in accordance **..

with any validity criterion and the determination of the : invalid output may be in response to any invalidity criterion. *5

According to an optional feature of the invention, the model means is arranged to generate expected outputs for only a subset of possible inputs to the at least one network element.

This may facilitate implementation and may specifically allow a low complexity yet efficient implementation. The alarm condition detection apparatus may specifically generate alarms only for this subset of possible inputs and may ignore all other inputs and outputs resulting from other inputs.

According to an optional feature of the invention, the model of the network element comprises a number of associations between specific input events and specific expected output characteristics. Specifically, the model may comprise a set of rules associating input messages to the at least one network element to expected output messages from the at least one network element.

This may facilitate implementation and may specifically allow a low complexity yet efficient implementation. The model may specifically be a set of rules that determines what specific outputs should result from what specific inputs. For example, rules may be included that specify characteristics of specific output messages that are expected from specific input messages.

According to an optional feature of the invention, the specific expected output characteristics comprise an output timing indication for an expected output event.

This may facilitate implementation and/or may allow accurate alarm condition detection. The output timing indication may for example indicate a time interval in which a specific output event, such as a communication of an output message, is expected.

According to an optional feature of the invention, the monitored output comprises output communication of the at least one network element.

This may facilitate implementation and/or may allow accurate alarm condition detection.

According to an optional feature of the invention, the alarm condition detection apparatus further comprises means for instigating a switch to redundant network element functionality for the at least one network element in response to the alarm.

This may increase reliability of the cellular communication system.

According to an optional feature of the invention, the alarm condition detection apparatus further comprises means for communicating an alarm indication to a different network element of the cellular communication system. The different * 15 network element may specifically be an Operations and Management Centre (OMC).

This may allow improved management of the cellular communication system and may in particular allow an efficient centralised processing of fault events. * . . * 0

According to an optional feature of the invention, the alarm indication comprises an indication of the at least one network element.

This may allow improved management of the cellular communication system and may in particular allow an efficient centralised processing of fault events.

According to another aspect of the invention, there is provided a cellular communication system comprising an alarm condition detection apparatus for a cellular communication system, the alarm condition detection apparatus comprising: monitoring means for monitoring the input and output of at least one network element of the cellular communication system; model means for determining an expected output from the network element in response to a monitored input to the network element by evaluating a model of the network element for the monitored input; and alarm means for generating an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element.

According to an optional feature of the invention, the cellular communication system further comprises a second network element and the alarm condition detection apparatus further comprises means for communicating an alarm IS** indication to the second network element. *I..

This may allow improved management of the cellular communication system and may in particular allow an efficient centralised processing of fault events. *. S

According to an optional feature of the invention, the second network element comprises means for presenting an alarm to a user in response to receiving the alarm indication from the alarm condition detection apparatus.

This may allow improved management of the cellular communication system and may in particular allow an efficient centralised processing of fault events by a network operator. The means for presenting may specifically be arranged to present an identification of the at least one network element to the user.

According to another aspect of the invention, there is provided a method of generating an alarm in a cellular communication system, the method comprising: monitoring the input and output of at least one network element of the cellular communication system; determining an expected output from the network element in response to a monitored input to the network element by evaluating a model of the network element for the monitored input; and generating an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element.

These and other aspects, features and advantages of the * 15 invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

* Brief Description of the Drawings

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which FIG. 1 illustrates an example of a cellular communication system in accordance with some embodiments of the invention; and FIG. 2 illustrates an example of an alarm condition detection apparatus in accordance with some embodiments of the invention.

Detailed Description of Some Embodiments of the Invention The following description focuses on embodiments of the invention applicable to a UMTS cellular communication system. However, it will be appreciated that the invention is not limited to this application but may be applied to many other cellular communication systems including for example GSM cellular communication systems.

FIG. 1 illustrates an example of a cellular communication system in accordance with some embodiments of the invention.

In a cellular communication system, a geographical region is divided into a number of cells each of which is served by a * 15 base station. The base stations are interconnected by a fixed network which can communicate data between the base 4 S stations. A remote terminal (e.g. a User Equipment (UE) or a mobile station) is served via a radio communication link by the base station of the cell within which the remote terminal is situated. 55. 4*

As a remote terminal moves, it may move from the coverage of one base station to the coverage of another, i.e. from one cell to another. As the remote terminal moves towards a base station, it enters a region of overlapping coverage of two base stations and within this overlap region it changes to be supported by the new base station. As the remote terminal moves further into the new cell, it continues to be supported by the new base station. This is known as a handover or handoff of a remote terminal between cells.

A typical cellular communication system extends coverage over typically an entire country and comprises hundreds or even thousands of cells supporting thousands or even millions of remote terminals. Communication from a remote terminal to a base station is known as uplink, and communication from a base station to a remote terminal is known as downlink.

FIG. 1 illustrates network elements of a fixed network of a UMTS cellular communication system. In the example base stations 101, referred to as Node Bs for UMTS cellular communication systems, support remote terminals or UE5 (not shown) over the UMTS air interface as will be well known to the person skilled in the art. * 15

The base stations 101 are coupled to Radio Network S...

Controllers (RNC5) 103. An RNC performs many of the control functions related to the air interface including radio resource management and routing of data to and from appropriate base stations. S.. * . S ** S

The RNC5 103 are coupled to a core network which for brevity and clarity is represented by two Serving GPRS Support Nodes (SGSN5) 105 in FIG. 1. A core network interconnects RNC5 and is operable to route data between any two RNC5, thereby enabling a remote terminal in a cell to communicate with a remote terminal in any other cell. In addition, a core network comprises gateway functions for interconnecting to external networks such as the Public Switched Telephone Network (PSTN), thereby allowing remote terminals to communicate with landline telephones and other communication terminals connected by a landline. Furthermore, the core network comprises much of the functionality required for managing a conventional cellular communication network including functionality for routing data, admission control, resource allocation, subscriber billing, remote terminal authentication etc. Specifically, the SGSN5 105 are arranged to interface the core network to the Radio Access Network (RAN) comprising the RNC5 103 and base stations 101. The SGSNs 105 provide for packet routing thereby enabling packet based fixed network communication. As will be known to the person skilled in the art, the fixed network will typically comprise other network elements including for example an Operations and Management Centre (OMC), which provide for * 15 management and control of the cellular communication system by a network operator, and Serving GPRS Support Nodes S... * S

(GGSN5) which provide for packet communication and interfacing to other communication systems such as the Internet or the PSTN. *5S

: Thus, fixed networks of cellular communication systems are very complex and have many different network elements interworking in complex and subtle ways. Furthermore, it is essential for cellular communication systems to have extremely high reliability such that any downtime and service disruption is minimised. It is therefore very important that fault conditions or other alarm conditions are quickly and accurately detected, identified and localised.

In the system illustrated in FIG. 1, each network element has an associated alarm condition detection apparatus 107 (henceforth referred to as an alarm unit) which is arranged to generate an alarm in response to a detection of a fault condition for the associated network element. However, in contrast to conventional systems, wherein fault detection tends to be an integral part of the individual network element, the alarm units 107 are separate and segregated units that do not have any direct interaction or shared functionality or resource with the network elements themselves. Rather, the alarm units 107 monitor the input and output communication from the associated network element 101-105 and detect fault conditions for the network elements 101-105 based only on this communication. Furthermore, the alarm units 107 are completely transparent to the network elements 101-105 and the fixed network as a whole. Thus, the : 15 operation of the individual network element 101-105 is completely independent of whether it has an associated alarm S...

unit 107 or not.

* FIG. 2 illustrates an example of an alarm condition detection apparatus (alarm unit) 107 in accordance with some S..

embodiments of the invention.

S..... * .

The alarm unit 107 comprises a monitoring processor 201 which is arranged to monitor the input and output of the associated network element 101-105.

The monitoring processor 201 comprises a network interface 203 which provides an interface to the network connection(s) of the associated network element 101-105. For example, for an RNC 103, the network interface 203 can provide an interface to the lub interface connections to the base stations served by the RNC 103 and/or to the lu interface connection to the SGSN 105.

The network interface interfaces to the connections in a transparent way, i.e. such that the presence of the alarm unit 107 does not affect the communication to and from the network element 101-105. This may e.g. be achieved by the network interface merely sensing the electrical signals on the physical connection without being inserted in the connection itself. As another example, the alarm unit 107 can be inserted in the connection(s) to the network element and can forward any message from one port to the other.

The network interface 203 is coupled to an input processor * *, 15 205 which receives the input communication to the network element and to an output processor 207 which receives the output communication from the network element. Specifically, any data packet transmitted to the network element may be fed to the input processor 205 by the network interface 203 and any data packet transmitted by the network element may : be fed to the output processor 207 by the network interface e * The input processor 205 is fed to a model processor 209 which is arranged to determine an expected output from the network element 101-105 in response to the input communications to the network element 101-105. Specifically, the model processor 209 comprises a model of the network element 101-105 which is indicative of an expected fault free operation. The model can typically be a relatively simple model which considers only a subset of the functionality of the network element.

As an example, the input processor 205 may have identified a number of input messages for which the model can determine an expected output. If one of these messages is received by the input processor 205, it is forwarded to the model processor 209 which proceeds to evaluate the model to determine the expected output.

As a simple example, the model processor 209 can determine that if a given predetermined input message is received, the network element should generate a specific output message.

For example, for an RNC 103, the detection of a user data packet received from the SGSN 105 for communication over the air interface to a remote terminal by a specific base station can lead to the model processor 209 determining that eaI* an output message addressed to the specific base station and a.. *

comprising the same user data should be outputted by the network element 101-105 on the connection to this base station. as,

.. : The model processor 209 and the output processor 207 are coupled to an alarm generator 211 which is arranged to generate an alarm in response to a detection of a discrepancy between the expected output determined by the model processor 209 and the monitored output from the network element as determined by the output processor 207.

For example, the output processor 207 may have a list of all output data messages which are generated in response to specific input messages and which should be predicted by the model processor 209. If any of these are detected, it is forwarded to the alarm generator 211.

If the received output message corresponds to an expected output message from the model processor 209, the alarm generator 211 determines that the network element is operating as expected and no alarms are raised. However, if no output message is detected corresponding to the output message expected by the model processor 209 within a suitable time interval, the alarm generator 211 determines that an unexpected operation of the network element 101-105 has occurred, and thus that a potential fault condition exists at the network element 101-105. Accordingly, it proceeds to generate an alarm indicative of this fault.

Thus, the alarm units 107 provide for an independent verification and detection of the operation of the individual network elements. Furthermore an accurate

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localisation of any faults can be achieved as each alarm unit 107 is allocated to a specific network element 101-105 and is arranged to only raise alarms if the malfunction occurs in that network element 101-105. I.

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In the system of FIG. 1, the alarm units 107 are isolated and segregated from the associated network elements 101-105.

Specifically, in the example the alarm units 107 use independent networking and computing resources to make them independent from the network elements 101-105. The grade of segregation can be varied depending on whether some shared resources are used and the segregation of the alarm units 107 can e.g. be classified by the following levels: -Network level: This is a low level of segregation achievable wherein the alarm units 107 have an independent management connection. Thus the alarm reporting and control of the alarm units 107 is separated from the management and control of the network element 101-105.

-Software level: This can be considered an intermediate level of segregation where the alarm unit 107 is contained within an independent software module but allowing some hardware resource to be reused for the software of the alarm unit 107 and of the network elements 101-105. This may provide independency from bad transitions or software glitches as the operation 15 of the software of the network element 101-105 is verified by a completely independent process and using a completely independent algorithms and criteria.

Typically, the alarm unit verification software 4.

implementing the model of the network element 101-105 will be designed and developed completely independently : of the design and development of the network element software and preferably by a completely different design team.

-Hardware level: This can be considered a maximum grade of segregation which can include the network level and/or software level segregation. For this level of segregation, completely different hardware can be used toimplement the alarm unit 107, which can also be powered by a completely independent power supply.

Specifically, the implementation may be such that no hardware resources are shared between the network element 101-105 and the alarm unit 107 which can be a completely separate hardware entity interfacing only with the network element 101-105 through the transparent monitoring of input and output communications for the network element 101-105.

Increasing segregation of the alarm unit 107 can provide an increasing reliability of the alarm generation and in particular may allow an increased probability of the detection of faults that may occur in the network element 101-105. For example, software segregation during both the operation and design phase can allow spurious fault conditions which have not previously been contemplated or realised to be detected. Furthermore, segregation reduces * ** 15 the risk of a single fault affecting both the network element 101-105 and the associated alarm unit 107 thereby SI** * 0 providing a more reliable alarm generation.

* Sell * I In the system of FIG. 2, the alarm units 107 are completely independent units that interact with the network elements S..

.. : 101-105 only through the transparent monitoring of the input and output communications. The alarm units 107 are therefore segregated both at the network level, the software level and the hardware level.

Furthermore, in the system of FIG. 2 each alarm unit 107 is associated with only a single network element 101-105 and will raise alarms only for faults occurring within that individual network element 101-105. It will be appreciated, that in some embodiments one or more of the alarm units 107 may be associated with a group of network elements and may detect faults occurring within that group of network elements. Thus, the alarm unit may monitor the input and output communications for the network elements of the group and may raise alarms if the output communications do not correspond to the expected output for those inputs.

Thus, in the system of FIG. 1, each alarm unit 107 is associated with single or a group of network elements 101- 105. This enables a fault detection philosophy based on independent fault areas thereby allowing a facilitated localisation of faults. Each alarm unit generates fault reports for the specific network element or group of network elements with which it is associated and for which it has a model. This allows alarm detection performance which is not associated with outages (link down, not service, etc), but with behaviours. The alarm unit verifies if the output is correct for a given input, avoiding error propagation through components. Only the alarm unit monitoring the faulty element will generate an alarm. Specifically, other alarm units monitoring connected network elements will * 20 detect that an incorrect input is received and will therefore not generate an alarm as the alarms will only be generated if an invalid output is generated in response to a valid input. Thus, the alarm is generated only for the network elements where the error originates and consequential error performance in connected equipments do not give rise to any additional alarms. This may substantially facilitate the localisation of network faults.

It will be appreciated that the model processor 209 can implement a complex model of the behaviour and operation of the associated network element but that it in many embodiments can be a very simple model of the expected behaviour of the network element. This can allow a lower cost, complexity and high reliability of the alarm unit.

Specifically the model may simply comprise a set of associations between specific input events and expected output characteristics. For example, a number of input messages to the network element may be specified and for each of these input messages an expected output event may be assigned. The output event can specifically be that a message having a certain set of characteristics is outputted by the network element within a given time interval.

The specified set of input messages for which an output event is defined may in some embodiments correspond to all possible input messages to the network element. However, in many embodiments only a subset of input messages is used by the alarm unit. This may reduce the complexity of the alarm S...

unit and in particular may allow a simplified model to be implemented. Furthermore, it may allow a facilitated S.....

* 20 monitoring of the output from the network element and a facilitated alarm detection operation. Also, for a typical * : network element, only some input messages typically result in well-defined and easy to monitor output events occurring.

In such embodiments, if a message is received for which the input processor 205 detects that an expected output event is defined by the model, it will forward this message to the model processor 209 and the expected output will be fed to the alarm generator 211 for comparison to the monitored output.

However, any other input message received by the network element is ignored by the alarm unit. In particular, any invalid or erroneous input messages that may potentially give rise to an erroneous output is automatically ignored by the alarm units thereby preventing that an alarm is raised in response to a fault that has occurred in another network element.

Thus, in the specific embodiment, an alarm is generated only if an invalid output message is detected to arise from a valid input message comprised in the subset of input messages for which expected outputs are defined.

In the example of FIG. 2, the model processor 209 simply comprises a set of rules associating the input messages of the subset to expected output messages from the network ::. element. * . S...

Specifically, for each input message of the subset, the *IS...

model processor 209 has a list of one or more output messages that should be generated by the network element in : response to the input message. For each output message a number of characteristics is defined which allows the alarm generator 211 to compare the monitored output with the expected output. The characteristics may be different for different output messages and can for example include an indication of some of the data comprised in the data message, a destination for the output message and/or an expected timing of the output message (such as a maximum delay before the message should be generated).

The model processor 209 can for example comprise a simple look-up table which for each defined input message comprises a set of expected output message(s) with specific characteristics for these messages.

As a specific example, an alarm unit for an RNC can comprise an entry in the look-up table which corresponds to the RNC receiving a user data packet message which is to be broadcast in a plurality of cells. For such a message, the look-up table may indicate that a number of output messages addressed to the base stations supporting the cells in which the data is to be broadcast should be generated and outputted by the RNC. The entry may further specify a maximum delay of these messages as well as other characteristics.

When the RNC receives such an input message, this is a..... detected by the alarm unit and the input processor 205 forwards the message to the model processor 209 which in * . *.. S * 20 response provides the information of the expected output messages to the alarm generator 211. When receiving this : information, the alarm generator 211 sets a timer to a maximum delay before which the output messages should be outputted from the network element. The output processor 207 monitors the output messages and forwards any user data packet messages for the base stations to the alarm generator 211. Each of these messages is compared to the characteristics for the expected output messages and if a complete match is found, the corresponding message is removed from the list of expected output messages. If any output messages still remain at the end of the maximum delay as indicated by the timer, the alarm generator 211 has detected a discrepancy between the expected output and the monitored output and accordingly it proceeds to generate an alarm.

It will be appreciated that the alarm unit can operate at different layers of the protocols used for the network communication. For example, the alarm unit may monitor characteristics of the physical layer and set an alarm in response to any discrepancy at this level. Alternatively or additionally, the model may comprise information of higher layer characteristics thereby allowing the alarm generator to verify operation within these layers.

For example, typical data messages received and transmitted by the network elements comprise layered or nested * information relating to the different protocol layers and the alarm unit may be arranged to verify information and * S.. S *

characteristics of the different layers.

* 20 It will be appreciated that an alarm generated by an alarm unit may be used for different purposes in different *::: : embodiments.

S.....

For example, in some embodiments the alarm unit may comprise means for causing a switch to redundant network element functionality in response to the detection of a fault condition for the network element.

Specifically, many cellular communication systems comprise a redundant network element or redundant modules of network elements which may be used to replace a malfunctioning network element or module of the network element. As a simple example, if an alarm unit detects that its associated network element has developed a fault, it may generate an alarm in the form of a control signal which is fed to an internal or external switch unit that can switch between the original network element and a redundant network element.

In many embodiments, the network element itself comprises a number of redundant modules that may replace other modules of the network element in case of a malfunction. In such an example, the alarm control signal can be fed to the network element thereby causing the network element to shift from a malfunctioning module to a redundant module. Specifically, different alarms can be raised depending on the nature of the detected discrepancy and the module which is switched to a redundant module may depend on the exact alarm that has : been generated. I... S... * .

This may increase the reliability of the communication system as a whole and/or may reduce the downtime of a system ***...

* 20 and/or may reduce the need for manual intervention.

In many embodiments, the alarm generated by the alarm unit is communicated to a different network element of the * S communication system. For example, an alarm can be reported to network elements that are directly connected to the malfunctioning network element thereby causing these network elements to change their behaviour in order to compensate for the fault. For example, an alarm generated for a given routing network element in the fixed network can be reported to be network elements coupled to it. In response to receiving such an alarm, these network elements can proceed to attempt to route any data packet via data paths that do not include the malfunctioning network element.

In some embodiments, the alarms may be reported to a centralised Operations and Management Centre used by the network operator to control and manage the operation of the cellular communication system. The received alarms from different alarm units may be presented to users of the OMC, and specifically the network operator may be made aware of any fault conditions existing in network elements throughout the fixed network. This will facilitate operation and management and will allow the network operator to take compensating action. Specifically, the reported alarm can indicate the type of alarm which is being reported as well as the source of the alarm (i.e. an indication of the malfunctioning network element). This information can be presented to the network operator thereby providing for a detailed and accurate fault description and localisation.

* 20 The described system tends to provide a number of advantages and benefits including one or more of the following: * ** * * * ** * * It facilitates fault diagnosis as fault reports are directly mapped to affected network elements.

* It improves management availability as bad transitions and crashes in the network element software do not affect the alarm function thanks to the independent hardware, software and network resources.

* It reduces the probability of false alarms and increases reliability. E.g. network elements can enter faulty states through transitions which have not been contemplated or realised during the development. In such states it is not possible to ensure that the network element is able to accurately evaluate the operation and accordingly it may provide erroneous fault detection. An external monitoring function will not be affected by such behaviour.

* Reusability. Each alarm unit can be intended for a specific network element and can be developed and manufactured based only on the specifications of the network element. The alarm unit can thus be generic for the specific type of network element and can be used with different network elements, different systems etc. * It will be appreciated that the above description for clarity has described embodiments of the invention with *S.* reference to different functional units and processors.

However, it will be apparent that any suitable distribution of functionality between different functional units or processors may be used without detracting from the : invention. For example, functionality illustrated to be performed by separate processors or controllers may be performed by the same processor or controllers. Hence, references to specific functional units are only to be seen as references to suitable means for providing the described functionality rather than indicative of a strict logical or physical structure or organization.

The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented at least partly as computer software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may * appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, * 20 the term comprising does not exclude the presence of other elements or steps. * ** * 0 I

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also the inclusion of a feature in one category of claims does not imply a limitation to this category but rather indicates that the feature is equally applicable to other claim categories as appropriate. Furthermore, the order of features in the claims does not imply any specific order in which the features must be worked and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. * ** * * *** *

* S 55 S...

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Claims

CLAIMS

1. An alarm condition detection apparatus for a cellular communication system, the apparatus comprising: monitoring means for monitoring the input and output of at least one network element of the cellular communication system; model means for determining an expected output from the network element in response to a monitored input to the network element by evaluating a model of the network element for the monitored input; and alarm means for generating an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element.

*
2. The alarm condition detection apparatus of claim 1 wherein the alarm condition detection apparatus has a *e*.

management network connection which is independent of management network connections of the at least one network element.

:
3. The alarm condition detection apparatus of claims 1 or 2 wherein software of the alarm condition detection apparatus is segregated from software of the at least one network element.

4. The alarm condition detection apparatus of any of the previous claims wherein hardware of the alarm condition detection apparatus is segregated from hardware of the at least one network element.

5. The alarm condition detection apparatus of any of the previous claims wherein the alarm condition detection apparatus has an independent power source from the at least one network element.

6. The alarm condition detection apparatus of any of the previous claims wherein the alarm condition detection apparatus is uniquely associated with a group of network elements comprising the at least one network element.

7. The alarm condition detection apparatus of any previous claim wherein the alarm means is arranged to generate an alarm only if an invalid output from the at least one network element is detected for a valid input to the at least one network element. * ** *

8. The alarm condition detection apparatus of any previous as.. * 5

claim wherein the model means is arranged to generate expected outputs for only a subset of possible inputs to the at least one network element.

: 9. The alarm condition detection apparatus of any previous claim wherein the model of the network element comprises a number of associations between specific input events and specific expected output characteristics.

10. The alarm condition detection apparatus of claim 9 wherein the model comprises a set of rules associating input messages to the at least one network element to expected output messages from the at least one network element.

11. The alarm condition detection apparatus of claim 9 or wherein the specific expected output characteristics comprises an output timing indication for an expected output event.

12. The alarm condition detection apparatus of any previous claim wherein the monitored output comprises output communication of the at least one network element.

13. The alarm condition detection apparatus of any previous claim further comprising means for instigating a switch to redundant network element functionality for the at least one network element in response to the alarm.

14. The alarm condition detection apparatus of any previous claim further comprising means for communicating an alarm indication to a different network element of the cellular S...

communication system.

S

* 20 15. The alarm condition detection apparatus of claim 14 wherein the different network element is an Operations and : Management Centre (OMC).

S.....

16. The alarm condition detection apparatus of claim 14 or 15 wherein the alarm indication comprises an indication of the at least one network element.

17. A cellular communication system comprising an alarm condition detection apparatus for a cellular communication system, the alarm condition detection apparatus comprising: monitoring means for monitoring the input and output of at least one network element of the cellular communication system; model means for determining an expected output from the network element in response to a monitored input to the network element by evaluating a model of the network element for the monitored input; and alarm means for generating an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element.

18. The cellular communication system claimed in claim 17 further comprising a second network element and wherein the alarm condition detection apparatus further comprises means for communicating an alarm indication to the second network element. * .. . ***. * *

19. The cellular communication system claimed in claim 18 wherein the second network element comprises means for presenting an alarm to a user in response to receiving the alarm indication from the alarm condition detection a..

: apparatus. * a

20. A method of generating an alarm in a cellular communication system, the method comprising: monitoring the input and output of at least one network element of the cellular communication system; determining an expected output from the network element in response to a monitored input to the network element by evaluating a model of the network element for the monitored input; and generating an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element. * .* 4* p * S S...

S * * . *Sp

S S S S. a

0**sS* * p Amendments to the claims have been filed as follows

CLAIMS

1. An alarm condition detection apparatus for a cellular communication system including at least one network element coupled by network connections, the apparatus comprising: monitoring means for monitoring an input and an output of the at least one network element of the cellular communication system; model means for determining an expected output from the output of the network element in response to a monitored input to the input of the network element by evaluating a model of the network element for the monitored input to determine the expected output; and alarm means for generating an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element.

2. The alarm condition detection apparatus of claim 1 wherein the alarm condition detection apparatus has a fault management network connection to the communication system which is independent of the network connections of the at least one network element.

3. The alarm condition detection apparatus of claims 1 or 2 wherein software of the alarm means is segregated from software of the at least one network element.

4. The alarm condition detection apparatus of any of the previous claims wherein hardware of the alarm means is segregated from hardware of the at least one network element.

5. The alarm condition detection apparatus of any of the previous claims wherein the alarm means has an independent power source from the at least one network element.

6. The alarm condition detection apparatus of any of the previous claims wherein the alarm means is uniquely associated with a group of network elements comprising the at least one network element.

7. The alarm condition detection apparatus of any previous claim wherein the alarm means is arranged to generate an alarm only if an invalid output from the at least one network element is detected for a valid input to the at least one network element.

8. The alarm condition detection apparatus of any previous claim wherein the model means is arranged to generate expected outputs for only a subset of possible inputs to the at least one network element.

9. The alarm condition detection apparatus of any previous claim wherein the model of the network element comprises a number of associations between specific input events and specific expected output characteristics.

10. The alarm condition detection apparatus of claim 9 wherein the model comprises a set of rules associating input messages to the at least one network element to expected output messages from the at least one network element.

11. The alarm condition detection apparatus of claim 9 or wherein the specific expected output characteristics 3% comprises an output timing indication for an expected output event.

12. The alarm condition detection apparatus of any of claims 8 to 10, further comprising a list of output data messages which are generated in response to specific input messages to the at least one network element.

13. The alarm condition detection apparatus of any previous claim further comprising means for instigating a switch to redundant network element functionality for the at least one network element in response to the alarm.

14. The alarm condition detection apparatus of any previous claim wherein the alarms means communicates an alarm indication to a different network element of the cellular communication system connected to the network element.

15. The alarm condition detection apparatus of claim 14 wherein the different network element is an Operations and Management Centre (OMC).

16. The alarm condition detection apparatus of claim 14 or wherein the alarm indication comprises an indication of the at least one network element.

17. A cellular communication system including at least one network element coupled by network connections and comprising an alarm condition detection apparatus for the cellular communication system, the alarm condition detection apparatus comprising: monitoring means for monitoring an input and an output of the at least one network element of the cellular communication system; model means for determining an expected output from the output of the network element in response to a monitored input to the input of the network element by evaluating a model of the network element for the monitored input to determine the expected output; and alarm means for generating an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element.

18. The cellular communication system claimed in claim 17 wherein the alarm condition detection apparatus further comprises means for communicating an alarm indication to a user in response to receiving the alarm indication from the alarm condition detection apparatus.

19. The cellular communication system claimed in claim 17 wherein the model means models characteristics of at least one specific protocol layer of the communication system and the alarm means sets an alarm in response to any discrepancy at this at least one specific protocol layer.

20. A method of generating an alarm in a cellular communication system including at least one network element coupled by network connections, the method comprising: monitoring an input and an output of the at least one network element of the cellular communication system; determining an expected output from the output of the network element in response to a monitored input to the input of the network element by evaluating a model of the 1o network element for the monitored input to determine the expected output; and generating an alarm in response to a detection of a discrepancy between the expected output and the monitored output of the at least one network element.