It became evident after closer analysis of the projected corporate model, that in order to maintain a viable business and to achieve profit goals, Tymshare, Inc. must consolidate its computers into one location and transfer the computer power from that location to where it was needed. The challenge was immediately evident: communication capability at reasonable cost. The need was equally evident that this communication capability had to be dependable, error free, and interactive. Tymshare chose to develop its own network from the communication common carrier service. This network, which Tymshare calls TYMNET, is presently in service using 80 Tymshare-built TYMSAT communication computers. Each TYMSAT uses a Varian Data 620 computer. Each step in the development of this network resulted from the solution of specific problems, often bringing new problems to light in the process of solving old ones.