lar user’s field of vision and cognizance. The opportunity to explore and learn on one’s own has been correspondingly limited and channeled, affecting both self-realization and autonomy. 11 The “tightness” of this Deleuzean feedback loop—its bandwidth and precision—is particularly troubling.

Cellular Architecture,
Cellular Databases

What it is about the cellular network that makes it so surveillance friendly, and a potential threat to the individual user and to society? The answer lies in a series of design choices, choices made in an attempt to solve the problem of establishing and maintaining contact with a mobile user. The details have filled many books (see, for example, Etemad, 13 Holma and Toskala, 22 Kaarenenetal et al., 24 and Mouly and Pautet. 30), but we need only trace the path of a call that is incoming to a cellular user to see how personal data is being collected and put to use.

The coverage area of a cellular network is partitioned into relatively small areas called cells, with each cell receiving a subset of the radio resources of the overall network. Two cells may be assigned identical spectral resources— a process called frequency reuse—if the cells are far enough apart to prevent their radio transmissions from interfering with each other. A cell tower sits at the center of each cell, establishing connections between mobile users and the wired cellular infrastructure. Location areas are defined to consist of one or a small number of cells. As we will see, the location area is the finest level of granularity used by the network in trying to complete a call to a cellular platform.

We now consider an incoming call. To complete an incoming call to a cellular phone, the network routes the call to a mobile switching center (MSCt) that is near the phone. Through a process called paging, the MSC then causes the called cellular phone to ring. When the cellular user answers his or her phone, the MSC completes the call and communication can commence.

 

t As space is limited and such details are not important to the theme of this article, I will not attempt to track vocabulary distinctions between second-, third-, and fourth-generation cellular systems.

It remains possible,
however, to
secure cellular
networks against
surveillance.

In order to perform this routing and paging process, the network must keep track of the location of the cellular telephone. This is done through the registration process. All cellular telephones that are powered on periodically transmit registration messages that are received by one or more nearby cell towers and then processed by the network. The resulting location information thus acquired is stored with varying levels of granularity in several databases. The databases of interest to us here are the Home Location Register (HLR) and the Visitor Location Register (VLR). The HLR is a centralized database that contains a variety of subscriber information, including a relatively coarse estimate of the subscriber’s current location. HLRs are generally quite large; there need be only one per cellular network. VLRs, generally associated with local switches, contain local registration data, including the identity of the cell site through which registration messages are received. There is typically one VLR per mobile switching center (MSC) or equivalent.

The VLR stores the identification number for the cell site through which the registration message was received. The identity of the MSC associated with the VLR is forwarded to the Home Location Register (HLR) that maintains the records for the registering platform.

We can now track the progress of an incoming call in more detail. Calls from outside the cellular network will generally enter the network through a gateway MSC. The gateway MSC will use the called number to identify and query the appropriate HLR to determine how to route the call. The call is then forwarded to the MSC associated with the last registration message, which in turn queries the VLR to determine in which location area to attempt to contact the subscriber. The base station controller associated with the location area then causes a paging message to be sent to the called cellular telephone, causing it to ring. If the subscriber answers the call, the MSC connects a pair of voice channels (to and from the cellular platform), and completes call setup.

The HLR and VLRs (or equivalents) are thus the sources of the historic and prospective cell site data discussed earlier in the survey of telephone privacy law.