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Enhancing Mobile Device Location Using the Identification Triplet

A hand tapping a mobile phone with location pin graphics overlaid

Mobile location services used by Law Enforcement (LEAs) and Intelligence Agencies to identify and locate devices and subjects of interest are typically focused on the MSISDN (Mobile Station International Subscriber Directory Number) identifier. This represents the number we would normally consider as our phone, or cell, number. Under the covers, however, the mobile networks actually use an IMSI (International Mobile Subscriber Identity) to identify a subscriber account and manage communication. It is this identifier that law enforcement agencies may intercept during field operations using an ‘IMSI catcher‘. The handset itself also has a unique identifier, the IMEI (International Mobile Equipment Identity). Together, these three identities are often referred to as a ‘triplet‘.

Whilst any one of the triplet identifiers can be used to locate a mobile device, most mobile location applications and platforms are focused on the MSISDN. Supporting identification through all three identifiers, the MSISDN, IMSI and IMEI, will provide the LEA community with the capabilities they really need to reduce crime, prevent terrorism, and save lives.

Follow the SIM or Follow the Handset?

A locate request based upon an IMSI or MSISDN will allow the tracking of a subscriber’s SIM (Subscriber Identity Module) or eSIM card. Locating a device using the IMEI is asking a very different question, however. Tracking the handset instead allows for the detection of SIM swapping – both the use of multiple SIMs within a single handset, and the use of a single SIM card in multiple devices. Investigators can even potentially determine if a handset is being shared between subjects of interest.

This is an important capability that can improve the law enforcement and intelligence community’s ability to locate and track criminal activities. Unfortunately, its use is not as widespread as one would hope or expect. IMEI-based location requests require integration with the EIR (Equipment Identity Register) to obtain the last known triplet for a device, and CSP/vendor support for such lookups is not uniform.

The Need for Standardization

The EIR is an established element in mobile networks, and as part of standard operations will have access to the identifier triplet. But there are currently no standards for interfaces to expose the last known triplet either through a MAP or HTTP interface. This does lead to an inconsistent ability for location platforms to support IMEI-based location requests, as standard location interfaces with the mobile networks require either an IMSI or MSISDN as an identifier.

As part of a location lookup, it is possible that all three identifiers, the IMSI, IMEI and MSISDN, are obtained through interactions with network elements. Unfortunately, the most common location service standard, MLP (Mobile Location Protocol), does not provide the capability to return all known identifiers. It is possible to obtain the IMSI as additional information through the gsm_net_param element, but there is no functionality to return the IMEI. Alternatively, if the only identifier analysts have is an IMEI, a locate request using MLP will not return the corresponding MSISDN. These shortcomings need to be addressed to fully serve LEA needs and protect society.

Although vendors do have the capability to provide additional information using the standard interface via a custom extension mechanism defined within MLP, it would require bespoke integration, which can create dependence on a particular vendor. SS8 offers such a custom extension to support all known identifiers to our lawful and location intelligence clients, but we recognize that such capabilities should be integrated into the standards to enhance and streamline device identification and location for investigators.

SS8 therefore calls upon standards bodies such as ETSI and 3GPP to draft standardized protocols to support lookups of the latest triplet and to communicate all device and subscriber identities to law enforcement and intelligence agency analysts. Such capabilities would allow simple integration of location solutions with network elements while also enhancing interoperability and vendor-agnostic architectures. Even if the locate request does not successfully position the device or subscriber, a response including all known identifiers expands the available information about a subject of interest, improving investigative outcomes.

About Neil Stamps

SS8 Senior Engineer Neil StampsNeil Stamps is a Senior Software Engineer in the SS8 location team. He has a BSc in Computer Science and over 35 years of experience in software development, including 15 years in location services. Neil is responsible for business services within SS8’s location platform – providing interfaces, validation, and routing capabilities that support a variety of customer needs and deployment configurations. He is passionate about providing the capabilities that emergency services and intelligence communities require and was a key team member of the European Commission Help 112 project to roll out AML to Europe. You can learn more about Neil on his LinkedIn profile here.

About SS8 Networks

As a leader in Lawful and Location Intelligence, SS8 helps make societies safer. Our commitment is to extract, analyze, and visualize the critical intelligence that gives law enforcement, intelligence agencies, and emergency services the real-time insights that help save lives. Our high performance, flexible, and future-proof solutions also enable mobile network operators to achieve regulatory compliance with minimum disruption, time, and cost. SS8 is trusted by the largest government agencies, communications providers, and systems integrators globally.

Intellego® XT monitoring and data analytics portfolio is optimized for Law Enforcement Agencies to capture, analyze, and visualize complex data sets for real-time investigative intelligence.

LocationWise delivers the highest audited network location accuracy worldwide, providing active and passive location intelligence for emergency services, law enforcement, and mobile network operators.

Xcipio® mediation platform meets the demands of lawful intercept in any network type and provides the ability to transcode (convert) between lawful intercept handover versions and standard families.

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