Location Privacy Mechanisms in 3GPP

Cellular network specifications are a useful starting point when LCS concepts are being discussed. This is because LCS functionality is relatively mature in this category of networks. Using the 3GPP specification as a point of reference, the functionality in place in support of privacy can be studied and some general principles can be derived. The discussion of privacy legislation highlighted that four types of location requesters are pertinent :

• Those with implicit permission
• Those with explicit permission
• Emergency services
• Law enforcement

Implicit permission exists where access to, and use of, the location information is associated with an existing service arrangement. A clear example of this is the cellular telephony service itself. In order to route a call to a subscriber, the cellular network needs to locate that subscriber, at least to the precision of the current serving cell. That is, locating the person and using the location information is part and parcel of the service arrangement, is understood in principle as being required to provide that service, and implicit permission to do so therefore exists. Emergency services are well understood as a service in which permission to provide location is offered implicitly in the act of dialing the service. This is essentially an example of implicit permission. The principles of legislation, however, indicate that location may also be disclosed where there are reasonable grounds to believe that the person's or other persons' safety may be in danger. In this case, the requester of location effectively assumes that the person would give their permission if they could. If any network privacy constraints exist, a mechanism by which they can be overridden is required in this kind of scenario.

Explicit permission is more obvious. This can occur at the time of a location request-when a notification is sent to the person's handset indicating that a particular person would like the location of the handset. A positive response is explicit permission to provide that location in this particular instance. Alternatively, permission may be provided in advance. For instance, the handset location may be provided to any predefined group of "friends" who may be authenticated by a PIN or other mechanism. Law enforcement agencies are typically provided with privileged access to information which would otherwise be held in confidence when it is necessary to proceed with investigations relating to crime and/or national security. These privileges are generally defined in some separate legislation relating to these activities. Due process incorporating the desired checks and balances will normally require the application and granting of a warrant or other formal permission before the information can be accessed and used. As for emergency services, a network mechanism is required that permits properly controlled requests for location in a valid lawful requirement scenario.

To see how 3GPP supports these different requester types, reference is made to the Stage 2 LCS specifications. The "portal" through which applications may request location in a 3GPP network is called the gateway mobile location center (GMLC). To begin with, LCS clients can be placed in one of four categories:

• Emergency Services
• Value Added Services
• PLMN Operator Services
• Lawful Intercept Services