WO2009007795A1

WO2009007795A1 - Media server selection for lawful interception within a call control system

Info

Publication number: WO2009007795A1
Application number: PCT/IB2007/053440
Authority: WO
Inventors: Jayaraman Venkata Subramanian; Rosendo Vas Rodrigues; Gerhard G. Langenbucher; Norbert Reher
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2007-07-10
Filing date: 2007-07-10
Publication date: 2009-01-15
Anticipated expiration: 2010-01-10

Abstract

The present invention relates to a control system (CCS) having trunks to receive setup signaling messages for setting up call sessions in a communication network, means to detect that a setup signaling message corresponds to a service requiring a duplication to be happened to the originator of said setup signaling message and/or to the called subscriber/user, and a media server (MS) to duplicate and forward the content of said call session to a duplication destination (LEA) according to said duplication service detection. This call control system further comprises means for determining said media server (MS) according to the geographical region of said media server (MS), said geographical region being determined at least from a key verification relative to said setup signaling message.

Description

Media server selection for lawful interception within a call control system

The present invention relates to packet duplication in packet based telecommunications networks, and particularly to Internet Protocol (IP) based. In particular, the present invention relates to a media server for lawful interception in IP telecommunications networks.

Lawful interception (Ll) is the legally sanctioned official access to communications, such as telephone calls or e-mail messages, of a user under surveillance. LI is defined as the method of tracking the activities of a person who can be termed legally not good.

The term "media server" (MS) as used herein preferably connotes any entity which copies communication content for duplication. For example, a media server might be a media gateway, a media server or any communication content copy function CCCF.

Classically, LI is played using a media resource function server comprising a media server MS and a media gateway controller (MGC). The communication content (CC) is duplicated in the MS and forwarded to a duplication destination, for example a law enforcement agency (LEA).

Since the number of intercepted subscriber is going on in the increase and not decreasing, the total successful calls in a large network with higher number of targets will go down and it becomes highly desirable to duplicate from the nearest media server MS relative to the geographical region of the called subscriber/user.

This is of particularly higher importance where the NGN network covers Intelligent Networks (IN) and local traffic as well, as the quantum of interception to be happened per day/hour would be significantly higher. Furthermore, the Applicant set itself the problem of providing a call control system enabling to have the nearest media server selected to have the duplication of all types and for all purposes.

The aim of the invention is to solve these issues. It relates to a call control system having trunks to receive setup signaling messages for setting up call sessions in a communication network, means to detect that a setup signaling message corresponds to a service requiring a duplication to be happened to the originator of said setup signaling message and/or to the called subscriber/user, and a media server to duplicate and forward the content of said call session to a duplication destination according to said duplication service detection.

According to a general definition of the invention, said call control system further comprises means for determining said media server according to the geographical region of said media server, said geographical region being determined at least from a key verification relative to said setup signaling message.

According to embodiments of the invention, this determination of said geographical region of said media server depends on a Calling Line Identity, contained in said setup signaling message, or on the identifier of the trunk from which said setup signaling message has arrived, or on the number of the called party, or on the trunk for which said signaling message is destined.

The call control system may comprise matching table for mapping values of said media servers and said geographical regions.

The call control system may comprise also matching table for mapping values of said geographical regions and said Calling line identities and/or said identifiers of trunks and/or said Called numbers.

The invention consists also on a communication network comprising such a call control system.

At last, another object of the invention is a method for controlling calls comprising a step of transmitting setup signaling message to a call control system for setting up call sessions in a communication network, a step of detection that a setup signaling message corresponds to a service requiring a duplication to be happened to the originator of said setup signaling message and/or to the called subscriber/user, and a step implemented in a media server for duplicating and forwarding the content of said call session to a duplication destination in response to the detection step.

This method is characterized in that it further comprises a step of determining said media server according to the geographical region of said media server, said geographical region being determined at least from a key verification relative to said setup signaling message.

The invention would be more clearly explained in the following description, with the help of the annexed figures.

The figure 1 illustrates a communication network comprising a call control system according to the invention. The figure 2 is a flowchart illustrating the steps relative to the determination of the nearest media server, according to the invention.

In the figure 1 , the communication network CN comprises a call control system CCS. This call control system can receive setup signaling message from various calling devices (telephone, IP terminals, etc.), Tl , T2,

T3, located in several geographical areas or regions RGl , RG2, RG3 corresponding to local communication networks, LNl , LN2, LN3, respectively.

Typically, these setup signaling messages may be compliant with the

SIP protocol ("Session Initiation Protocol") as defined by the RFC 3261 of the IETF (Internet Engineering Task Force). In case of a converged call control system, like a media gateway control (MGC), the setup signaling messages can arrive from plain-old telecommunication networks (POTN) and be compliant with the ISLJP protocol ("ISDN User Part"). The aim of the setup signaling messages (e.g. the "Invite" message of the SIP protocol) is to set up a call session between the calling device and a called device (not shown in the figure).

As said previously, Lawful Interception LI is played using a media resource function server comprising a media server MS and a media gateway controller MGC or call control system CCS . The communication content CC is duplicated in the MS and forwarded to a duplication destination, for example a law enforcement agency LEA. In such a situation, it is the responsibility of the call control system CCS to trigger the duplication of the communication content of the call session.

Typically again, the duplication is realized in a least one media server MS, separated from the call control system itself.

The communication between the call control server CCS and a media server MS could be based on existing control or signaling protocols, e.g. H.248; SIP or the HTTP protocol (HyperText Transfer Protocol). The destination address of the duplication destination LEA could be a Directory number or an URL (Uniform Resource Locator). Typically, the communication content CC is sent via a mediation function from the media server MS to the LEA. However, it can be sent optionally also directly to the LEA. Knowing the destination address of the duplication destination LEA, or the mediation function, respectively, the call control server CCS can order the media server MS to forward the duplicated communication content of the calling party that has emitted the setup signaling message to the mediation function or directly to the LEA. In practice, the entire country is divided into regions RG, and for each region RG a least one corresponding media server MS is associated.

For example, the media server MSl corresponds to region RGl .

The determination of the nearest media server able to duplicate and forward the communication content to the duplication destination LEA depends on the region corresponding to the setup signaling message (i.e. requested by the calling party and/or the called party).

In practice, the call center system CCS uses information relatives to the setup signaling message and extracts the region RG in which the duplication is to be happened. A free media server MS within the identified region RG is then selected and the duplication is triggered.

As shown in the figure 1 , trunk Tl links the call control system CCS to the local communication network LN l belonging to region RGl ; the trunk

T2 links it to the local communication network LN2 belonging to region RG2; and the trunk T3 links it to the local communication network LN3 belonging to region RG3.

According to the trunk identifier, the call control server CCS can determine which media server MS is present within the region RG corresponding to the local communication network LN. For instance, if the media server MSl is located in a region RGl where the local communication network LN l is identified by the trunk identifier, then the media server MSl would be chosen.

The Calling Line Identity (CLI) could also be used for selecting the media server. This Calling Line Identity CLI is typically the number of the party initiating the call, as defined by the recommendation E.164 of the ITU-T (International Telecommunication Union). This number is made of several parts as defined by the numbering plan. The prefix of the Calling Line identity CLI represents the region (geographical area). Using this prefix, the call control system CCS can therefore determine the media server. However, this calling line identity CLI is not mandatory and could be not present in the setup signaling message.

With reference to figure 2, a flowchart has been represented illustrating the selection of the appropriate media server.

At step SOl , during the active phase of the call, the calling line identity CLI is examined. If received, the CLI is extracted to find out the region identifier RG id of the region it belongs to (step S02).

In practice, CLI is the key to a table (for example called " TRANSLAREACOD") used for translation of received CLI (area code) into the corresponding region identifier RG id.

In case the CLI is not present, the unique trunk group identity (trunkgroup id) is used to obtain the region identifier RG id (step S03).

In practice, trunkgroup id is the key to a table (for example called "TKGIDLANID") used for translation of received trunkgroup identifier into the corresponding region identifier.

At step S04, the region identifier RG id thus obtained is processed.

If the region identifier RG id thus obtained is found in a table (called "Media server table") for mapping of region id to media server id (step S05), said corresponding media server identifier MS id is used (step SOό) to select the appropriate media server (step S07).

In case the region identifier RG id is not present in the media server table or in case the media server is not found, any media server would be selected (step S08).

In practice, each time the media server table is accessed, first a check is performed on whether the media server is active, enabled, etc. before a comparison is made on the required region identifier RG id and the region identifier RG id entry provided for the media server entry accessed in the table.

After the entire table is scanned, if no match is found, then any found valid media server (for example, the last or the first active, enabled, etc. media server that is found) is selected.

In a variant, in case there is no media server found within the desired region, instead of selecting any media server, a solution is to select a media server from the neighboring region.

For duplication to be provided on called subscriber communication content CC, the called number or outgoing trunkgroup identifier can be used to access the tables to obtain the region identifier id. The region identifier to media server identifier mapping is the same as that for the CLI case. The tables themselves can be generic, and do not distinguish between CU/called number or incoming/outgoing trunkgroup id. In other words, the present invention is similar when duplication have to be happened on called party communication content ("CLI" replaced by called number, "incoming trunk id" replaced by "outgoing trunk id").

According to one embodiment of the invention, the Calling Line identity is used when it is present. When it is not, then the trunk identifier is used instead for determining which media server to select.

According to the invention, the call control system CCS contains means to match with each possibility of value for the calling line identity CLI and/or trunk identifiers, an address to the appropriate media server. These means could for instance be a simple matching table (s). It is therefore quite easy for the operator of the system to modify this table in order to change a region to another, to add a new media server etc.

The present invention provides tremendous savings for both the network operator as well as the LEA.

For network operator, savings in usage of expensive network resources (especially in large countries), both in term of number as well as the duration of use, no loss of LI content communication call data which is very much important for the LEA and hence reducing the risk of threats in the country.

For transmission delay, the present invention avoids delay of the original conversation.

For the LEA, basically all information is always available to the LEA and hence the network becomes more reliable for the Law enforcement agency.

Furthermore, cost savings are also obtained in case of optical fiber connections to the distant media server.

Claims

1 ) Call control system (CCS) having trunks to receive setup signaling messages for setting up call sessions in a communication network, means to detect that a setup signaling message corresponds to a service requiring an interception to be happened to the originator of said setup signaling message and/or to the called subscriber/user, and means to duplicate and route the content of said call session to a third party (LEA) via a media server (MS) according to said interception service, characterized in that it further comprises means for determining said media server (MS) according to the geographical region of said media server (MS), said geographical region being determined at least from a key verification relative to said setup signaling message.

2) Call control system according to claim 1 , in which said the determination of said geographical region (RG) of said media server (MS) depends on a Calling Line Identity (CLI), contained in said setup signaling message.

3) Call control system according to claim 2, in which said determination of said geographical region (RG) of said media server (MS) depends on the identifier of the trunk from which said setup signaling message has arrived, when the Calling Line Identity (CLI) is not available. 4) Call control system according to claim 1 , in which said determination of said geographical region of said media server (MS) depends on the number of the called party.

5) Call control system according to claim 4, in which said determination of said geographical region of said media server (MS) depends on the trunk for which said signaling message is destined, when the called number is not present.

6) Call control system according to one of the previous claims, further comprising a matching table, mapping values of said media servers and said geographical regions.

7) Call control system according to claim 2, further comprising a matching table, mapping values of said geographical regions and said Calling line identities.

8) Call control system according to claim 3 or claim 5, further comprising a matching table, mapping values of said geographical regions and said identifiers of trunks.

9) Call control system according to claim 4, further comprising a matching table, mapping values of said geographical regions and said Called numbers.

10) Communication network comprising a call control system according to one of the previous claims.

11 ) Method for controlling calls comprising a step of transmitting setup signaling message to a call control system (CCS) for setting up call sessions in a communication network, a step of detection that a setup signaling message corresponds to a service requiring an interception to be happened to the originator of said setup signaling message and/or to the called subscriber/user, and a step for duplicate and route the content of said call session to a third party (LEA) via a media server (MS) according to said interception service, characterized in that it further comprises a step of determining said media server (MS) according to the geographical region of said media server (MS), said geographical region being determined at least from a key verification relative to said setup signaling message.