Terminal handling protocols in a packet-switched public data network

Abstract

The diversity of terminals available is a major issue for an administration providing a public data transmission service. The only fair terminal handling policy is to use standard interfaces, and persuade users and manufactures to adapt to these standards, which are the CCITT Recommendations X.25, X.3, X.28, X.29. The virtual call, accessible through X.25, may be the basis of a transport service. Some ways of using PAD services provided by public data networks (in other words of defining protocols between terminal's operator and computer) are: in a real mode of operation, the terminal, seen by the computer through the PAD, looks very much like the real one, or emulates a slightly different one; in a virtual terminal mode, the computer talks to a standard terminal; the mapping of existing real terminals to this virtual terminal is done locally at the user-to-PAD interface, without the computer having to know the specifications of each real terminal; in a PAD-to-PAD mode, the service emulates a direct connection via an asynchronous leased or switched access.