The infrastructure of Iran's internal internet connectivity is based on two major networks. One is the Public Switched Telephone Network (PSTN) to support connections based on modems. PSTN provides a connection for end-users to ISP's over mostly digital voice lines (see Chapter 3).
The second major internal Internet connectivity is provided by the Public Data Network (PDN) operated by DCI as an independent subsidiary of the Telecommunication Company of Iran (TCI). We provide here an overview of this network. For more details on DCI see also Section 4.3.9.