was a consistent understanding of the end points of the connection; that is, all calls went from one fixed point to another fixed point. This had the great merit, from a business standpoint, of clearly defining who was going to pay the bill for the call time; that is, the caller, unless one reversed the charges by calling collect, in which case the call receiver paid for the call. The terrestrial lines to the local telephone were always available, meaning that the capacity of the system was limited by the number of switch to switch circuits that could be created.

In the 1970’s, technology was developed that would provide for a switch to telephone connection made by way of a radio frequency channel that did not require a fixed, terrestrial line; the concept was termed cellular telephony. In the United States, a section of the radio frequency spectrum in the range of 800 MHz was allocated for mobile telephony. Communication in this frequency range is rather limited, with distances between the end-point telephone and the switching station that it talked to being typically in the 10 to 30 kilometer range. Given this range limitation and the rather minimal allocation of total radio frequency spectrum, an architecture was devised that allowed individual switching stations to use a variety of frequencies, with the available spectrum divided up into many carrier channels, each capable of supporting a single voice call. Each switching station was said to support a cell, with adjacent cells alternating frequencies to minimize cross channel interference for telephones equidistant from two or more different receivers. The switch to which the end-point telephones, now termed handsets, would connect was termed a cell base-station. Handsets, as it turns out, would be the first personal electronic devices, and, to this day, the most numerous.

As the network developed, phone companies, and later countries, entered into agreements for charging each other their respective share of the technical consumables associated with each phone call. All these agreements were implemented in central switches which routed the calls to their proper destination while at the same time, accounting for them.

In the 1980’s, electronics had gotten to a point where it was possible to put, in a cost effective manner, a mobile phone handset in the hands of the general public. Each handset would communicate by radio to nearby antennas that would be associated with equipment allowing the routing of voice to the telephone operator company office, and from there to the general telephony network.

By far the most successful system is GSM (Global System Mobile), whose users had passed 1 billion in numbers at the turn of the XXI^st century, and passed 2 billion a few years later. If you own a mobile phone, it is most likely a GSM phone. As we’ve seen in Chapter 4, the GSM network was, from the start, designed with a trusted computer component at its heart; a smart card called a Subscriber Identity Module (SIM). Every GSM phone has one. The mobile telecommunication network was in fact, the first general network to have addressed straight on the issue of security. This actually became necessary for the simple reason that as long as the telephony network had been relying on a physical cable to the house, hacking into the network would call for tapping into that wire somewhere, something which was not impossible to do, and was actually done, but something that required a physical intervention that could relatively easily be detected and dealt with by the existing legal systems.

When communities were established in a wide manner over the air, the story changed. It would now be possible for somebody to hack into the system by simply communicating via radio with the antenna of the telephone. Henceforth came the idea of associating with the handset the Subscriber Identity Module, i.e. a secure repository of user information. If the mobile phone

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