Authentication in Analogue Telephone Access Networks

Theft of communication resources in public telephone access networks is a problem for many operators and their subscribers. In this paper we describe a practical solution to the problem of intruders connecting to other peoples analogue telephone lines and making calls on their charges. As main criteria, the solution must be simple to implement and cheap to introduce on a large scale, while giving strong protection. A challenge-response authentication protocol is found to be the most suitable mechanism, and the implementation is described in some detail