OA18756A - A System for Detection of a Bypass of an Interconnect to a Telecommunication Network. - Google Patents

Abstract

There is described a system (1) for detection of a bypass (540, 840) of an interconnect (530, 830) to a telecommunication network (50, 80), the system (1) comprising: * means (10) adapted to originate a test call to or through a telecommunication network (50) under test from outside the telecommunication network (50) under test; * at least one receiver probe (20) with a subscription for terminating the test call, the subscription being configured with calling line identification restriction override (CLIRO); and * a control system (40) configured to: * initiate the test call; * receive from the receiver probe (20) call information comprising a received calling line identification (CLI) of the test call; and * detect the presence of the bypass (540, 840) by analysing the received calling line identification (CLI). According to the invention the control system (40) is further configured to detect the presence of the bypass (540) if the received calling line identification (CLI) belongs to a subscription to the telecommunication network (50) under test.

Description

A_SYSTEM FOR DETECTION OF A BYPASS OF AN INTERCONNECT TO A TELECOMMUNICATION NETWORK

Field of the Invention

The présent invention generally relates to a system for détection of an interconnect bypass in télécommunication networks, especially in wireless télécommunication networks such as for example of the type GSM, UMTS or similar, but also in wired télécommunication networks.

Background of the Invention

When a télécommunication network operator provides access from his network to a network of another télécommunication network operator and vice versa, both operators, by means of agreement or sometimes subject to regulatory requirements, set up a suitable interconnection facility which is subjected to extensive testing in order to assess technical reliability and the quality of service of the interconnection facility so that the agreed upon or regulatory standards are met. Next to the technical arrangements there are in many cases also interconnection charges that the télécommunication network operator receiving a call charges for the calls passing through the interconnection facility. When a calling party calls from another télécommunication network to the network of the télécommunication network operator of the receiving party, for example because the calling party is a client of another network operator than the receiving operator or because the calling party is abroad and is making use of a partnering network operator that provides roaming services for its network operator, this call has to pass through the interconnection facility.

Sometimes there are attempts to bypass the interconnection facilities of the network operator in an attempt to make money by avoiding at least a part of the interconnection charges. These attempts are made by bypass operators that reroute a part of the traffic of calling parties within the network of another operator to the network of the receiving operator without going through the interconnection facility. Generally these bypass operators make use of end user facilities from the receiving operator.

This leads to a direct loss of revenue for the receiving network operators and this leads to technical problems. First of ail as the bypass operator uses end user facilities to provide a network interconnection. Furthermore the use of these end user facilities and the setup of a new call créâtes an additional interface. Therefor there is a serious risk of quality problems such as degraded quality of audio or data transmissions, interruptions during the call, a prolonged waiting time during the call initiation, unacceptable delays in the transmissions,

-2. Further, because of the bypass operators reroute the call by setting up a new cal! making use of end user facilities of the receiving operator, the CLI of the calling party will be replaced with the CLI of the new call, This leads to inconveniences for the receiving parties which receive an erroneous or no CLI, but can also hâve more serious safety issues involved when a call to emergency services or police is involved. Furthermore this also creates serious technical difficulties for automatic téléphoné switchboards that operate on the basis of the CLI of the incoming call.

A system for setting up test calls in a télécommunication network is known from for example WO99/01974 and W02008/071857. These call charge vérification Systems generate a séries of calls between different sites on one or more networks to enable the network operator to check the billing procedure of the network. These Systems however rely on collection of billing data produced by the operator in order to extract data, such as for example the CLI for analysis. Therefor these Systems require access to sensitive data of the télécommunication network operator. This data is sensitive because it is reîated to the calling behaviour of its customers which might be subjected to privacy régulations or because it relates to billing information which is considered as commercial know how of the télécommunication network operator. These problems are especially relevant if the call charge vérification system is operated by third parties that offer such system as a service to the télécommunication network operator. As then extensive access by these third parties to information of the télécommunication network operator requires spécifie interfaces to be developed to provide access to the billing information for each spécifie télécommunication network operator. This is time and resource intensive and makes it difficult to scale the vérification System to multiple télécommunication network operators.

A known system that overcomes the abovementioned drawbacks is the Meucci system as described on their website: http://www.meucci-solutions.com . This System for détection of a bypass of an interconnect to a télécommunication network under test comprises means adapted to originate a test call to said télécommunication network under test from outside the télécommunication network under test and at least one receiver probe with a subscription for terminating said test call. Further this system comprises a control System configured to initiale the test call; receive from the receiver probe call information comprising a received calling line identification (CLI) of the test call; and analyse the received calling line identification (CLI) such that presence of the bypass can be detected. The Meucci system does not require an interface with the billing System. However in this case difficulties can arise for detecting and disabling a bypass when the bypass operator makes use of the CLIR function in order to mask the calling line identification of the subscriptions used in their bypass equipment as will be explained in further detail below.

-3US2010/0087191 mentions in its prior art section the existence of CLI based bypass détection Systems that make use of a subscription being configured with calling line identification restriction override (CURO). This document further describes a CLI based bypass détection system that requires test call data from both the originating side and the terminating side of the test call to be compared. Furthermore the disclosed system relies on timing information such as the time of initiation of the test call and the duration of the test call in order to be able to match originating and terminating call data that is available in roaming records and call data records. This is computationally intensive operation and it is not clear how this could be performed in real time, this means during the execution of a spécifie test call. Furthermore the system disclosed requires roaming subscription to the network under test. The disclosed system further also requires access to call data records and roaming records which might contain sensitive client data or commercial data that the operator of the télécommunication network under test does not want to disclose to third parties.

US2009/0069047 discloses a SIM box détection system that is based on statistical analysis of the call data records in order to detect a so-called wireless bypass signature. Such a system is not capable of a real time détection of a bypass and requires access to large amounts of sensitive subscriber data of the operator of the télécommunication network under test.

As such there is a need for a simple and robust system that can provide real time information about the availability of a bypass. This system should be able to be operated by third parties and should not requtre access to sensitive data of the télécommunication network operator nor should it require the interfaces to enable such access. The system should also allow identification and/or disabling of one or more subscriptions used in the bypass, even if the bypass operator makes use of the CLIR function in order to mask the calling line identification of the subscriptions used in their bypass equipment. Furthermore there remains the need for a system with reduced needs for test call data and computational resources.

Summary of the Invention

According to a first aspect of the invention there is provided a system for détection of a bypass of an interconnect to a télécommunication network, the system comprising: means adapted to originale a test call to or through a télécommunication network under test from outside the télécommunication network under test;

- 4 at least one receiver probe with a subscription for terminating the test call, the subscription being configurée! with calling line identification restriction override; and a control System configured to:

initiate the test call;

receive from the receiver probe call information comprising a received calling line identification of the test call; and detect the presence of the bypass by analysing the received calling line identification,

CHARACTERISED IN THAT the control System is further configured to detect the presence of the bypass if the received calling line identification belongs to a subscription to the télécommunication network under test.

This advantageously enables a simple and robust system for détection of a bypass that is able to detect a bypass even if the bypass operator makes use of a calling line identification restriction (CLIR) function in order to hide the CLI from détection. This enables to identify and subsequently disable the subscriptions that are being used in a bypass even if the bypass operator makes use of the CLIR function. When third parties provide the System for détection of a bypass as a service to a télécommunication network operator this requires neither access to sensitive data like for example billing date nor complex technical interfaces to provide that access. The third party only requires a subscription configured with CLIRO for terminating the test call.

This system further does not require complex computations nor extensive amounts of data to be able to detect the existence of a bypass. The control system only needs to analyse the received calling line identification (CLI) it receives from the receiver probe. No further information such as information regarding the originating side of the test call such as for example the calling party number is required for the analysis. There is also no longer a need for precisely scheduling the test calls at the originating side and no synchronisation of the originating means and the receiver probe is required in order to perform the test call. The advantageously reduced requirements for data and computational resources of the system according to the invention do not lead to any compromise in terms of robustness for détection of a bypass. The system according to the invention is able to reliably detect a bypass for every test call for which the received calling line identification belongs to a subscription of the télécommunication network under test.

According to an embodiment of the invention the subscription of the receiver probe (20) is a subscription to the télécommunication network (50) under test.

-5This allows for a straight forward setup that does not need a direct interface with the Systems of the operator of the télécommunication network under test. It is often possible for third parties which monitor the presence of a bypass to obtain a subscription configured with CLIRO from the operator of the network under test.

According to an alternative embodiment of the invention:

the subscription of the receiver probe is a subscription to a télécommunication network other than the télécommunication network under test; and the télécommunication network under test comprises a forwarding subscription which forwards the test call to the receiver probe.

As such a reliable détection of a bypass located in the télécommunication network under test becomes possible even in conditions in which there is only available a subscription configured with CLIRO for a télécommunication network outside the télécommunication network under test.

According to still a further embodiment ofthe invention:

the means is further adapted to originate the test call to or through the télécommunication network under test from outside the télécommunication network under test, and additionally from outside a further télécommunication network under test, the further télécommunication network under test being a télécommunication network other than the télécommunication network under test; and the control system is further configured to detect the presence of the bypass if the received calling line identification belongs to a subscription to the further télécommunication network under test.

This embodiment makes it possible to advantageously detect the presence of the so called ‘other operator’ bypass by analysing the CLÎ in such a way that real time détection of such a bypass is possible and without requiring a direct interface with the data or the technical Systems of the operator of the further network under test.

According to still a further embodiment of the invention:

the subscription of the receiver probe is a subscription to the further télécommunication network under test; and the means is further adapted to originate the test call to the subscription of the receiver probe;

the control System is further configured to detect the presence of an off-net bypass if the received calling line identification belongs to a subscription to the télécommunication network under test.

-6 This embodiment allows for a simple, reliable and real-time détection of an off-net bypass without requiring direct access to data or technical interfaces to the network under test nor to the further télécommunication network under test. Such off-net bypasses required complex analysis on extensive sets of data of multiple télécommunication network operators in prior art Systems.

According to an embodiment of the invention the détection of the bypass is implemented by checking if the received calling line identification (CLI) comprises a prefix which belongs to the numbering plan of the télécommunication network under test or alternative^ by checking if the received calling line identification (CLI) comprises a number which is comprised in the number database of said télécommunication network under test. This is a simple and reliable way to detect the presence of a bypass that is based on the insight that such a bypass makes use of a subscription to the network under test.

According to still a further embodiment of the invention the télécommunication network under test is located in a country with an associated country code, the means is adapted to originale the test call from a country other than the country of the télécommunication network under test, and the control System is further configured to detect the presence of the bypass if the received calling line identification comprises the same country code as the country code associated with said télécommunication network under test.

This allows for a fast and flexible détection that requires little computing power and a low amount of data to be transferred to the control System. It furthermore increases flexibility with respect to the means for originating test calls, as not only probes that are directiy controlled by the control System qualify, but also any means, operated automatically or manually that can originale test calls in a scheduled, unscheduled, ad hoc or random way.

According to a second aspect of the invention there is provided a method for detecting a bypass of an interconnect to a télécommunication network, the method comprising the steps of:

a means originating a test call to or through the télécommunication network under test from outside the télécommunication network under test;

at least one receiver probe with a subscription being configured with calling line identification restriction override terminating the test call; and a control System initiating the test call; receiving from the receiver probe call information comprising a received calling line identification of the test call; and detecting the presence of the bypass by analysing the received calling line identification, CHARACTERISED IN THAT

- 7 the control System detects the presence of the bypass if the received calling line identification belongs to a subscription to the télécommunication network under test.

According to an embodiment said method further comprises the steps of initiating, originating, receiving and analysing a plurality of test calts between a plurality of means and a plurality of predetermined receiver probes.

According to a further embodiment said method further comprises the steps of:

a scan phase wherein a first amount of the plurality of test calts is initiated at a first rate thereby identifying a bypass; and a shoot phase wherein a second amount of the plurality of test calls is initiated at a second rate only using predetermined means and predetermined receiver probes that are capable of passing through the bypass identified in the scan phase, the second amount and rate being higher than the first amount and rate respectively.

According to a third aspect of the invention there is provided a control System for use in a System according to the first aspect of the invention, characterised in that the control System is configured to:

receive call information comprising a received calling line identification of the test call from the receiver probe comprising the subscription for terminating the test call, the subscription being configured with calling line identification restriction override;

detect the presence of the bypass by analysing the received calling line identification, CHARACTERISED IN THAT the control System is further configured to detect the presence of the bypass if the received calling line identification belongs to a subscription to the télécommunication network under test.

According to a fourth aspect of the invention there is provided a receiver probe for use in a System according to the first aspect of the invention, characterised in that the receiver probe comprises the control System according to the third aspect of the invention.

This allows for a distributed setup of the control System that is able to advantageously make use of the computational resources that are already available within the hardware of the receiver probes.

Brief Description of the Drawings

- 8 Fig. 1 illustrâtes an embodiment according to the invention without the presence of a bypass;

Fig. 2 illustrâtes the embodiment according to Figure 1 with the presence of a bypass;

Figures 3 to 5 illustrate a further embodiment according to the invention with the presence of a bypass.

Detailed Description of Embodimentfs)

Figure 1 shows a System 1 for détection of a bypass of an interconnect 530 to a télécommunication network 50 under test. The system 1 according to the invention comprises a means 10 to originate a test call to said télécommunication network 50 under test from outside the télécommunication network 50 under test. This means 10 can be a suitable sender probe such as for example a GSM mobile phone or any other type of device capable of initiating a call on a predetermined outside télécommunication network other than the télécommunication network 50 of the network operator that is undertaking the investigation regarding the presence of a bypass of an interconnect 530, such as for example calling cards, a téléphoné number providing access to voip Systems, call back mechanisms, any type of pc originating calls, a suitable subscription to mobile networks such as for example a SIM card, wireline networks or call generators directly connected to télécommunication network equipment. The means 10 can comprise for example a fixed line subscription in the UK “+44 20 1234 5678 and the télécommunication network 50 under test can for example be a télécommunication network of a Belgian mobile operator with a numbering plan with a 474 prefix, this means “+32 474 xxx xxx”. The means 10 is for this purpose connected to a suitable control system 40 which enables to initiate the test call according to instructions received from this control system 40. The control System 40 is for example a suitably programmed computer that is directly connected to the means 10, but it might also be a remote computer system that is connected to the means 10 by means of a suitable network interface, such as for example a LAN or the internet, to enable exchange of instructions and/or data through this networks. It is clear that the system 1 for détection of a bypass is not limited to a system with only one means 10, it can however comprise any suitable number of means 10 dispersed among any suitable number of outside télécommunication networks. such as for example eight means 10 for different télécommunication networks in France and three means 10 for roaming télécommunication network partners in Ghana.

As can be seen in Figure 1 the bypass détection System 1 also comprises a receiver probe 20. This receiver probe 20 can for example also be a GSM mobile phone or any other type of device with a subscription for terminating the test call. The receiver probe 20 can for

-9example comprise a subscription to the télécommunication network 50 under test “+32 474 123 456. The receiver probe 20 is also connected to a suitable control system 40. The control system 40 receives from the receiver probe 20 call information comprising a received calling line identification (CLI) of the test call. It is clear that the System 1 is also not limited to a system with only one receiver probe 20. It can comprise any suitable number of receiver probes 20 with a subscription for terminating test calls.

The call information comprises a received CLI of the test call and optionally other data relating to the call such as for example the time and date the test call was exactly received, the time and date at which the test call started ringing, the time and date at which the test call was terminated, an indicator for whether the test call was picked up, the phone number associated with the means 20, the présentation indicator, ....

As shown in Figure 1 when no bypass is présent the control system 40 initiâtes the test call by activating the means 10 which subsequently originates the test call by calling the subscription to the télécommunication network 50 under test in the receiver probe 20. The test call is then sent to the télécommunication network 50 under test, for example optionally via one or more carriers 60. Subsequently the test call passes interconnect 530 of the télécommunication network 50 under test who routes the test call to the receiver probe 20. The receiver probe 20 then receives the incoming test call. It is not required for the receiver probe 20 to actually answer the test call. The control system 40 could for example be configured in such a way that it instructs means 10 to initiale the test call to the receiver probe 20 and to automatically disconnect the test call after aliowing three rings. The control system 40 then receives from the predetermined receiver probe 20 call information that comprises a received CLI, which is transmitted just before or after the first ring, and optionally other data conceming the test call. This could be done for example by downloading the call information from the receiver probe 20 to the control System 40 or by transmitting it to the control system 40 in any suitable way, by for example a wired or wireless connection means. The control system 40 then analyses the received CLI.

This analysis, as disclosed in prior art Systems, can be executed as a simple comparison with the calling party number associated with means 10 that the control System 40 instructed to initiale the test call. In the case illustrated in Figure 1 where the test call passed through the interconnect facility 530 this received CLI, for example “+44 20 1234 5678”, will match the calling party number, “+44 20 1234 5678“, associated with means 10 and the control system 40 will be able to détermine that for this test call no bypass was detected. This requires knowledge of the calling party number and also knowledge of the scheduling of the spécifie test calls as in this case information at the terminating side of the test call must be compared with information at the origination side of the spécifie test calls.

- 10However according to the invention, as the means 10 originales the test call from outside the télécommunication network 50 under test, the analysis can be done with even more reduced complexity and increased reliability. It can be determined whether the received CLI is a call that originated from within the télécommunication network 50 under test, this means an on net call, by for example analysing whether the prefix of the received CLI differs from the prefix associated with the numbering plan of the télécommunication network 50 under test If this analysis of the received CLI indicates the cailing party of the test call is not from within the télécommunication network under test, no bypass was detected. Thus as soon as the analysis is able to ascertain that the received CLI does not belong to the numbering plan associated with the télécommunication network 50 under test, no bypass within the network under test was detected. In order to also take into account number portability the analysis couîd comprise a check if the received CLI comprises a number which is comprised in the number database of the télécommunication network 50 under test. If this is not the case, no bypass within the network under test was detected. In general, because the means 10 originales the test call from outside the télécommunication network 50 under test, the presence of a bypass can be detected if the received CLI belongs to a subscription to the télécommunication network 50 under lest.

Another possibility for analysis is to check if the received CLI comprises the same country code as the country code associated the télécommunication network 50 under test. As the means 10 in many cases originales a test call from a country other than the one from the télécommunication network 50 under test this provides a tool for determining whether a bypass is présent.

Figure 2 shows the same System 1 according to Figure 1 in operation, but now there is a bypass 540 in place and this bypass 540 reroutes the test call. When the control System 40 now initiales a test call between means 10 and receiver probe 20 and the call is rerouted optionally via one or more carriers 60 to the bypass 540 a détection of the bypass 540 is possible as explained below.

Such a bypass 540, also known as for example a GSM gateway or SIM box when it concerns a wireless télécommunication network or a leaky PBX when it concerns a wired télécommunication network, is operated by interconnection bypass operators that route part of the traffic to the télécommunication network 50 under test from outside télécommunication network 50 via for example a suitable internet interface with one of the carriers 60 towards a bypass 540 which normally makes use of a plurality of subscriptions, for exampie “+32 474 111 222, that operate within the télécommunication network 50 under test and which convert the incoming test call into a new call originating from a subscription

- 11 to the télécommunication network 50, +32 474 111 222, and to the same destination and as such bypass the interconnect 530. However when the control System 40 now receives the receiver call information from the receiver probe 20 that received the test call initiated from means 10 and then analyses the received CLI.

This analysis, as disclosed above with reference to Figure 1, in prior art Systems, was executed as a comparison of the received CLI, ^u+32 474 111 222 with the calling party number, ''+44 20 1234 5678, associated with means 10, which in this case will not match. This is because instead of the calling party number of means 10, the calling party number of one of the subscriptions in the bypass 540, “+32 474 111 222, will be in the CLI received by receiver probe 20. The control System 40 is then able to assess that a bypass 530 is présent. This requires knowledge of the calling party number and also knowledge of the scheduling of the spécifie test calls as in this case information at the terminating side of the test call must be compared with information at the origination side of the spécifie test calls.

However according to the invention, as also explained above with reference to Figure 1, because the means 10 originales the test call from outside the télécommunication network 50 under test, the presence of a bypass 540 can be detected if the received CLI belongs to a subscription to the télécommunication network 50 under test. This can be implemented by checking whether the received CLI comprises a prefix which belongs to the numbering plan of the télécommunication network 50 under test “+32 474 xxx xxx” or when also taking into account number portability by checking whether the received CLI comprises a number which is comprised in the number database of the télécommunication network 50 under test. This reduces the complexity of the analysis and increases reliability. This also allows for flexibility in the means 10 that originate the test calls. As it is no longer necessary for the control System 40 to obtain call data from these means 10 or to be aware of the scheduling the spécifie test calls, the means 10 can be any means 10 that is able to originate a test call whether it is in a scheduled, unscheduled, automated, ad hoc or random way.

When the bypass 540 operator makes use of the CLIR function the System 1 would not be able to guarantee the détection of the presence and/or subséquent disabling of a bypass 540. The signais exchanged between télécommunication networks or within one télécommunication network when setting up a call namely comprise two fields, a CLI field which contains the calling party téléphoné number and a présentation indicator (PI) which indicates whether the CLI can be shown or not. The PI has three States: “available means that there is a CLI and it can be shown, “unavailable means that there is no CLI présent and Testricted means that there is a CLI present, but it cannot be shown to the destination subscription. When the bypass 540 operator enables the CLIR function for the subscriptions the bypass 540 makes use of, all calls from those subscriptions will be provided with a PI set

-12 to “restricted” and the last switch in the path will not pass on the CLI to the terminating subscription used in the receiver probe 20. A more detailed description of the CLIR function can for example be found in the ITU CCITT 1.251.4 spécification or the 3GPP TS 24.081 spécification.

Therefore the system according to the invention makes use of a receiver probe 20 that comprises a subscription to the télécommunications network 50 under test configured with a calling line identification restriction override (CLIRO) function. This is a feature implemented in the equipment of the télécommunication network 50. The feature will typically instruct the final switch in the path of the test call to ignore the PI if it is set to “restricted and still pas on the CL! to the terminating subscription of the receiver probe 20. Then, even if the bypass 540 makes use of a CLIR function the receiver probe 20 will always be able to detect the CLI of the incoming test call. This will enable the system 1 to detect and/or subsequently disable the spécifie subscriptions that are in use in the bypass 540.

In general the method for detecting the bypass 540 of the interconnect 530 to a télécommunication network 50 under test comprises the following steps:

the means 10 originale the test call to said télécommunication network 50 under test from outside the télécommunication network 50 under test;

the at least one receiver probe 20 with a subscription configured with CLIRO terminâtes said test call; and the control system 40 initiâtes the test call; receives from the receiver probe 20 call information comprising a received CLI of the test call; and detects the presence of the bypass 540 by analysing the received CLI.

In order to continuously monitor the télécommunication network 50 under test for the existence of a bypass 540 for its interconnects 530 with outside télécommunication networks the system 1 can initiale, originale, receive and analyse a plurality of test calls between a plurality of means 10 and a plurality of receiver probes 20. These receiver probes 20 each comprise a respective subscription to the télécommunication network 50 under test. Upon receiving from the plurality of receiver probes 20 the respective received CLI of the test calls, the control system 40 will analyse the respective received CLI as described above in order to detect the presence of a bypass 540.

As still a further refinement in order to allocate more resources of the system 1 to certain routes towards the télécommunication network 50 under test where the risk for bypass Systems 540 is higher, it is advantageous for the control system to initiate first a scan phase wherein a relatively low amount of test calls is initiated at a first rate, for example fifty calls at a rate of five test calls per day, in order to identifying suspect routes with an interconnect

- 13bypass. The control System 40 subsequently initiâtes a shoot phase wherein a higher amount of test calls is scheduled at a second rate, for example one thousand test calls at a rate of ten test calls per hour, only on these identified suspect routes. This then enables to identify as fast as possible as many as possible of the subscriptions used by the bypass 540 operating on these suspect routes in order to allow for subséquent disabling of these subscriptions.

According to an advantageous embodiment of the invention illustrated in Figure 3, it is not essential that the subscription configured with the CLIRO is comprised within the télécommunication network 50 under test. In this case the receiver probe 20 comprising the subscription with CLIRO forms part of a télécommunication network 80 different from the télécommunication network 50 under test. This could be for example because for the télécommunication network 50 under test there was no subscription with CLIRO available. In this case when a test call is initiated by the control System 40, means 10 originates a test call to a subscription 70 within the télécommunication network 50 under test. This subscription 70, also referred to as a forwarding subscription 70, however forwards the test call, via the interconnect 830 of télécommunication network 80, to the receiver probe 20 for terminating the test call, for example by putting the forwarding subscription 70 in unconditional forward mode. In this case similar as in Figure 2 the received CLI is provided by the receiver probe 20 to the control System for analysis even if the bypass 540 makes use of CLIR because the receiver probe 20 is provided with a subscription with CLIRO. Also in this case a similar analysis as in the embodiment in Figures 1 and 2 will enable détection of the bypass 540.

Figure 4 shows an alternative embodiment of the system 1 according to the invention. In this scénario the control system 40 initiâtes a call through the use of means 10 from outside the télécommunication network 50 under test to the receiver probe 20 with a CLIRO subscription to the télécommunication network 50 under test. In this case the call is routed, optionally via one or more carriers 60, to a bypass 840 that makes use of subscriptions to télécommunication network 80 other than the télécommunication network 50 under test, which we will refer to as a further télécommunication network 80 under test. It is clear that the means 10 additionally initiâtes the test call from outside this further télécommunication network 80 under test. The bypass 840 of the interconnect 830 of this further télécommunication network 80 under test couverts the incoming test call into a new call originating from a subscription to the further télécommunication network 80 under test to the same subscription in receiver probe 20. This further télécommunication network 80 under test then routes the test call to the interconnect 530 of the télécommunication network 50 under test and subsequently the test call gets terminated on receiver probe 20 with a CLIRO

- 14subscriptîon. The bypass 840 in this way bypasses the interconnect 830 from this further télécommunication network 80 under test. The control system 40 then receives the call information related to this test call from the receiver probe 20 and starts analysing the received CLI in order to détermine the presence of the so called ‘other operator’ bypass 840, by advantageously checking whether the received CLI belongs to a subscription to this further télécommunication network 80 under test. Normally this scénario only occurs when the télécommunication network 50 under test and the further télécommunication network 80 under test are in the same country. Therefore also in this embodiment a simple analysis of the country code of the received CLI or alternative^ an analysis whether the received CLI comprises a prefix which belongs to the numbering plan associated with the further télécommunication network 80 under test would enable the control system 40 to detect the bypass 840. Generally the bypass 840 is detected if the received CLI belongs to a subscription to this further télécommunication network 80 under test. In this case the operator of the télécommunication network 50 under test receives an interconnect charge from the operator of the further network 80 under test because its interconnect 530 is used, but ail the above mentioned quality problems associated with the presence of a bypass remain présent in this embodiment.

Figure 5 shows a further embodiment of the system 1 according to the invention. It is clear that the situation in the embodiment of Figure 5 is analogous to the embodiment of Figure 4, but here the bypass 540 makes use of subscriptions to the télécommunication network 50 under test and the receiver probe 20 is located in the further télécommunication network 80 under test, other then the télécommunication network 50 under test. This means that the receiver probe 20 comprises a subscription to this further télécommunication network 80 under test. This is a situation that can for example arise if there are available in the télécommunication network under test 50 subscriptions with retail rates that are lower than the interconnection rate to the further télécommunication network 80 under test. After receiving from the receiver probe 20 the received CLI the control system 40 can start the analysis in order to ascertain the presence of a so called ‘off net’ bypass 540. As explained above also in this embodiment a simple and robust analysis can be performed because the control system 40 would be able to ascertain the presence of an off net bypass 540 based on a portion of the CLI that is indicative of the télécommunication network 50. If this portion is présent in the CLI, the control system 40 has detected a bypass 540, because for the bypass 540 to bypass the interconnection 530 of the télécommunication network 50 under test, in this embodiment, it opérâtes with subscriptions to this télécommunication network 50 under test. Another possibility for analysis by the control System 40 could be to check whether the received CLI belongs to the number database associated with the télécommunication network 50 under test as this would then allow to take into account

- 15number portability. Also in this embodiment a simple analysis of the country code of the received CLI or alternatively an analysis whether the received CLI comprises a prefix which belongs to the numbering plan associated with the télécommunication network 50 under test would enable the control System 40 to detect the bypass 540 because for the bypass 540 to bypass the interconnection 530 of the télécommunication network 50 under test, in this embodiment, it opérâtes with subscriptions to this télécommunication network 50 under test. Generally the bypass 540 can be detected if the received CLI belongs to a subscription to a télécommunication network 50.

It is clear that the control System 40 and the télécommunication network under test 50 can be located in the same country or could be in a different country. Receiver probe 20 and télécommunication network under test 50 are normally in the same country, although in case of a mobile télécommunication network under test 50, probe 20 could be located outside this télécommunication network 50 under test with the CLIRO subscription to the télécommunication network under test 50 thus roaming on another network in another country. It is further also possible that the control System 40 is formed as a central System located on one site or alternatively as a geographically distributed System, in this case the functionality of control System 40 could for example be located within the receiver probe 20 or within the means 10. It is also clear that the control System 40 analyses the CLI information obtained through the CLIRO subscription.

Although the présent invention has been illustrated by reference to spécifie embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the présent invention may be embodied with various changes and modifications without departing from the scope thereof.

As such, for example, the embodiment shown in Figure 5 can be further elaborated with the concept shown in Figure 3 if for example no subscription with CLIRO would be available in télécommunication network 80. It is further not essential for the télécommunication network 50 under test and the télécommunication network 80 to be in the same country.

The system for détection of bypass according to the invention as described above can also be advantageously used as a CLI based call quality check system. In this context the system will be able to detect quality problems related to the received CLI of the test calls if for example the control system 40 receives from the receiver probe 20 a received calling line identification that belongs to a subscription to the télécommunication network 50 under test. It is clear that also the other embodiments of the bypass détection system described above could equally form a suitable basis for a CLI based call quality check System.

- 16The présent embodiments are therefore to be considered in ail respects as illustrative and not restrictive, the scope of the invention being indicated by the appended daims ratherthan by the foregoing description, and ail changes which corne within the meaning and range of equivalency of the daims are therefore intended to be embraced therein. In other words, it is contemplated to cover any and ail modifications, variations or équivalents that fall within the scope of the basic underlying principles and whose essential attributes are daimed in this patent application. It will furthermore be understood by the reader of this patent application that the words comprising or comprise do not exclude other éléments or steps, that the words a or an do not exclude a plurality, and that a single element, such as a computer System, a processor, or another integrated unit may fulfil the functions of several means recited in the daims. Any référencé signs in the daims shall not be construed as limiting the respective daims concerned. The terms first, second, third, a, b, c, and the like, when used in the description or in the daims are introduced to distinguish between similar éléments or steps and are not necessarily describing a sequential or chronological order. Similarly, the terms top, bottom, over, under, and the like are introduced for descriptive purposes and not necessarily to dénoté relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and embodiments of the invention are capable of operating according to the présent invention in other sequences, or in orientations different from the one(s) described or illustrated above.

Claims (13)

1. A System (1) for détection of a bypass (540, 840) of an interconnect (530, 830) to a télécommunication network (50, 80), the System (1) comprising:

• means (10) adapted to originale a test call to or through a télécommunication network (50) under test from outside the télécommunication network (50) under test;

• at least one receiver probe (20) with a subscription for terminating the test call, the subscription being configured with calling line identification restriction override (CLIRO); and • a control System (40) configured to;

o initiate the test call;

o receive from the receiver probe (20) call information comprising a received calling line identification (CLl) of the test call; and o detect the presence of the bypass (540, 840) by analysing the received calling line identification (CLl),

CHARACTERISED IN THAT the control System (40) is further configured to detect the presence of the bypass (540) if the received calling line identification (CLl) belongs to a subscription to the télécommunication network (50) under test.

2. A System according to claim 1, characterised in that the subscription of the receiver probe (20) is a subscription to the télécommunication network (50) under test.

3. A System according to claim 1, characterised in that:

• the subscription of the receiver probe (20) is a subscription to a télécommunication network (80) other than the télécommunication network (50) under test; and • the télécommunication network (50) under test comprises a forwarding subscription (70) which forwards the test call to the receiver probe (20).

4. A system according to any one of the daims 1 to 3, characterised in that:

• the means (10) is further adapted to originate the test call to or through the télécommunication network (50) under test from outside the télécommunication network (50) under test, and additionally from outside a further télécommunication network (80) under test, o the further télécommunication network (80) under test being a télécommunication network other than the télécommunication network (50) under test; and • the control System (40) is further configured to detect the presence of the bypass (840) if the received calling line identification (CLI) belongs to a subscription to the further télécommunication network (80) under test

5. A System according to claim 4 when dépendent on claim 1, characterised in that • the subscription of the receiver probe (20) is a subscription to the further télécommunication network (80) under test; and • the means (10) is further adapted to originale the test call to the subscription of the receiver probe (20);

• the control System (40) is further configured to detect the presence of an off-net bypass (540) if the received calling line identification (CLI) belongs to a subscription to the télécommunication network (50) under test.

6. A System according to any of the daims 1 to 5, characterised in that the control system (40) is configured to detect the presence of the bypass (540, 840) if the received calling line identification (CLI) comprises a prefix which belongs to the numbering plan of the télécommunication network (50, 80) under test.

7. A System according to any of the daims 1 to 5, characterised in that the control system (40) is configured to detect the presence of the bypass (540, 840) if the received calling line identification (CLI) comprises a number which is comprised in the number database of the télécommunication network (50, 80) under test.

8. A system according to any of the claim 1 to 5, characterised in that the télécommunication network (50, 80) under test is located in a country with an associated country code, the means (10) is adapted to originale the test call from a country other than the country of the télécommunication network (50, 80) under test, and the control System is further configured to detect the presence of the bypass (540, 840) if the received calling line identification (CLI) comprises the same country code as the country code associated with the télécommunication network (50, 80) under test.

9. A method for detecting a bypass (540, 840) of an interconnect (530, 540) to a télécommunication network (50, 80), the method comprising the steps of:

• a means (10) originating a test call to or through the télécommunication network (50) under test from outside the télécommunication network (50) under test;

• at least one receiver probe (20) with a subscription being configured with calling line identification restriction override (CLIRO) terminating the test call; and • a control System (40) initiating the test call; receiving from the receiver probe (20) call information comprising a received calling line identification (CLI) of the test call; and detecting the presence of the bypass (540, 840) by analysing the received calling line identification (CLI),

CHARACTERISED IN THAT the control system (40) detects the presence of the bypass (540) if the received calling line identification (CLI) belongs to a subscription to the télécommunication network (50) under test.

10. A method according to claim 9, characterised in that the method further comprises the steps of initiating, originating, receiving and analysing a plurality of test calls between a plurality of means (10) and a plurality of predetermined receiver probes (20).

11. A method according to claim 10, characterised in that the method further comprises the steps of:

• a scan phase wherein a first amount of the plurality of test calls is initiated at a first rate thereby identifying a bypass (540); and • a shoot phase wherein a second amount of the plurality of test calls is initiated at a second rate only using predetermined means (10) and predetermined receiver probes (20) that are capable of passing through the bypass (540) identified in the scan phase, the second amount and rate being higher than the first amount and rate respectively.

12. A control system (40) for use in a System according to any of the daims 1 to 8, the control system (40) being configured to:

• receive call information comprising a received calling line identification (CLI) of the test call from the receiver probe (20) comprising the subscription for terminating the test call, the subscription being configured with calling line identification restriction override (CLIRO);

• detect the presence of the bypass (540, 840) by analysing the received calling line identification (CLI),

CHARACTERISED IN THAT the control system (40) is further configured to detect the presence of the bypass (540, 840) if the received calling line identification (CLI) belongs to a subscription to the télécommunication network (50) under test.

13. A receiver probe (20) for use in a characterised in that the receiver probe (20) claim 12.

System according to any of the clàl comprises the control^system/(40) according t ί^Β.Ρ. 8211 Yaoundé )5|;