N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 1 - An Overview of the Communications Industry                                                              Slide 11 of 26 _________________                                                                                  __________

                                             Communications Services Evolution

                                        Voice

                                        Data (Asynchronous and Synchronous)

                                        Packet

_________________                                                                                  __________

The telephone companies Public Switched Telephone Network (PSTN) was designed for  voice communications in an analogue format. The PSTN facilities were used to transmit data by using datasets in an analogue format. The customers used teletype to enter data into the computers character by character (asynchronous) until the quality of terminals improved. The files between the controllers and the host used synchronous transmission. The next evolution in data transmission and networking was Packet transmission, similar to High-Level Digital Link Control (HDLC) developed by IBM and adapted as an international standard by International Standards Organization (ISO).

Until the 1970s telephone companies mainly provided voice (POTS) services. The telephone network also provided Dataphone (i.e. making connection with the other party by phone and then switching to the data transmission mode) and Private Line services. The POTS network was primarily designed for the telephone service.

The computer companies (IBM, DEC, HP) graduated from providing computer solutions to providing Integrated Solutions based on the proprietary protocols. The communications equipment suppliers included multiplexers in their Modem portfolio. Most of the data transmission was still Asynchronous and Synchronous.

The telecommunications industry threatened by growing proprietary private networks, deployed facilities (DataRoute) and packet (DataPac) networks to meet growing communications demand. More intelligence to make decisions on routing and error control was added to the networks.

The data networks were limited in capability and in providing customers with analogue and digital services.