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Lawful Interception in 3G IP Multimedia Subsystem

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Presentation on theme: "Lawful Interception in 3G IP Multimedia Subsystem"— Presentation transcript:

1 Lawful Interception in 3G IP Multimedia Subsystem
Author: Toni Mäki, Nokia Networks, Supervisor: Prof. Raimo Kantola

2 Agenda Network Architectures Lawful interception Goals of the thesis
Capturing the signalling Capturing the user data Correlating the signalling and user data

3 3G Architecture PSTN CS Domain IMS Internet Access Network PS Domain
Terminal Access network provides radio connectivity and most of the mobility handling CS domain provides traditional mobile voice service plus some new 3G services like video call PS domain provides packet based connectivity to existing packet based networks, that is the Internet IMS provides introduces the IP multimedia services, like VoIP. It provides SIP based signalling. Access Network PS Domain

4 IP Multimedia Subsystem (IMS)
Offers mechanisms for multimedia services like VoIP, gaming, Push-over-Cellular Based on Session Initiation Protocol (SIP) IMS handles only signalling, GPRS used as a bearer technology. Users identified by their SIP URI (e.g. or TEL URI (e.g. tel: )

5 IP Multimedia Subsystem
IMS Signalling Layer to other 3G CSCF MGCF to PSTN/GSM MRCF to Internet / other GGSN Signalling Path to PSTN/GSM Data Path GGSN MGW MRFP SGSN GPRS Core IMS Transport Layer RAN

6 Lawful Interception Authorities capture the communications of certain users in order to tackle criminal activity Ability to perform lawful interception may be a precondition for a licence to operate telecommunications network Lawful interception is a very delicate issue. IRI (Interception Related Information) contains signalling, interception activation statuses, etc… CC (Content of Communications) contains the actual communications transmitted or received

7 Lawful Interception in GPRS
The packet traffic of a user is tunnelled over the GPRS network to the Internet. These tunnels are recognised and captured in lawful interception for GPRS. All the tunnels of targeted user are delivered to authorities. All the GPRS signalling related to monitored user is captured (e.g. network attach, tunnel creation etc…) Lawful interception in GPRS is based on traditional GSM user identifiers (IMSI, MSISDN, IMEI)

8 Lawful Interception in GPRS
GGSN LIE SGSN LIC LIE LIB USER ATTACHED Lawful Interception Controller (LIC) controls the interceptions and provides management interface Lawful Interception Browser (LIB) buffers, refines and delivers the captured data and signalling RAN GPRS Core

9 Goals of Thesis Design/refine the interception of IMS related IRI
Design the interception of IMS related CC Very wide problem definition One task was to find out the problems

10 Methodology The messaging was analysed using signalling flows
Standards were thoroughly studied

11 LI in IMS (IRI) All the SIP messages transmitted, received or executed on behalf of the user must be delivered to the authorities Interception is activated based on SIP URI or TEL URI CSCF recognises the SIP messages to be captured by looking into the ’To’ and ’From’ fields in the SIP message header. CSCF also checks for the implicit registrations

CSCF LIE Signalling Path Data Path LIC LIP Path GGSN LIE SIP messages SGSN LIB LIE GPRS Core

13 Problems of CC LI in IMS IMS handles only signalling traffic
CC interception has to be executed in GPRS User identifiers used in IMS and GPRS differ SIP URI cannot be used in GPRS interception activation A mapping functionality must be provided SIP URI – GPRS user identity mapping is not one to one Current lawful interception mechanism uses user level of precision, which causes an illegal scenario

14 Problems of CC LI in IMS IMS Gi SGSN Gi GPRS Core

15 LI in IMS (CC) CPS notifies the LIC about the created sessions
LIC creates GPRS interceptions for CC collection CPS notifies the LIC about released sessions LIC releases the GPRS interception resources

16 LI in IMS (CC) Solution 1 GPRS interception is activated using IMSI
Existing network elements may co-exist The out-of-call packets need to be filtered out, before the data is forwarded to the authority

SessionStarted Get IMSI IMSI Activate Interception Activate Interception Activation Response Activation Response data CC data FILTERING To LEA

18 LI in IMS (CC) Solution 2 GPRS interception is activate using the IP flow identifiers as target identifier Quicker activation and less burden to the network The CC interception is done only at the IMS entry point, GGSN

SessionStarted Activate Interception Activation Response Activate Interception Activation Response data data CC data To LEA

20 Correlation numbering
The authority needs to correlate different kinds of IRI and CC. (e.g. the GPRS resources used by an IMS session The authority needs to be able to easily group the IRI belonging to the same session together

21 Correlation Numbering
IMS IRI carries Session Correlation Number, List of GPRS Correlation Numbers GPRS IRI carries only GPRS Correlation Number IMS CC carries GPRS Correlation Number, Session Correlation Number, and Media component identifier

22 Correlation numbering
SIP IRI Event 1 CC Data 1 GPRS IRI Event 1 GPRS CN 1 GPRS CN 1 GPRS CN 1 Session CN Session CN MC CN 1 SIP IRI Event 2 CC Data 2 GPRS IRI Event 2 GPRS CN 1 GPRS CN 2 GPRS CN 2 GPRS CN 2 Session CN Session CN MC CN 2

23 Conclusions IRI monitoring including the implicit registration
Capturing of content of communications in GPRS Correlation numbering scheme

24 Thank you for listening!
QUESTIONS? Thank you for listening!

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