Société Internationale de Télécommunications Aéronautiques

(SITA) Neuilly France

INTRODUCTION

1.1. SITA (Société Internationale de Télécommunications Aéronautique), a cooperative company founded in 1949, embraces the majority of the international air carriers (more than 160). It provides to its members a worldwide message switching network.

1.2. Initially the network consisted of manual (torn-tape) centres, interconnected by low speed circuits (50, 75 Bauds, 60, 30, 15 words per minute, asynchronous). The Airline terminal equipment (teleprinters. Telex) was connected to the SITA manual centres, thus enabling airline messages to be exchanged via nodes of the SITA network, with consequent reduction in costs to the airlines by their sharing of communications facilities.

1.3. With the rapid development of the Air Transport Industry, the airline communications needs became increasingly important and thus the SITA network expanded very quickly, by 1963 covering the world. Network development was not, however, restricted to geographic extension; in 1963 a number of the busiest manual centres were replaced by semi-automatic systems, and three years later, due to the continuing steady increase of traffic volumes, SITA equipped the Frankfurt centre with its first computer system to perform the message switching functions. Then, in 1969, SITA began replacing the other most heavily loaded centres (Western Europe and New York) with computer systems and established a computer communication data network by interconnecting these centres with voice grade circuits (medium speed). This network, called the High Level Network, performing the task of block switching, was interfaced at that time with the rest of the network composed of manual centres. This step was soon followed by the automation of other manual centres using what are in SITA terminology called satellite processors. These stand-alone computers act as concentrators of airline teleprinter traffic and controllers of airline CRT terminals, each of them connected to one High Level Centre by medium speed circuits. By mid-1973, the SITA network comprised 150 centres including 8 high level centres and 21 satellite processors. The 29 automated centres will be referred to as the SITA medium speed network (see figure 1).