Digital Simulation of Complex Traffic Problems in Communications Systems

This is a report on a method that was devised for simulating on a digital computer the performance of a large, complex communications system. The communication system consisted of many interconnected switching centers, each center having a large number of trunk groups attached to it. Each trunk group has access, through the switching centers, to any other trunk group located anywhere in the system. In order to conform as closely as possible to reality, the computer was programmed to simulate the performance of a human operator(s) at each of the switching centers. A method for simulating a completely automatic switch system was also devised. The computer logic was flexible enough to account for (1) any routing doctrine (or operator procedure), (2) any type of traffic distribution (Poisson or otherwise), (3) any configuration with any interconnecting facilities, and (4) a large number of trunk group inputs. Outages of either individual lines or entire switching centers due to equipment failure were treated. For a given traffic input, system configuration, and method of servicing calls, system performance data were taken in terms of the following parameters (1) Per cent completed and lost calls at each center and for the over-all system (2) Per cent of calls lost for various reasons (e.g., excessive waiting, busyness of subscriber facilities) (3) Utilities of operators and trunk lines (4) Distribution of and average waiting time. Successful runs were made on a digital computer whose storage capacity was 1000 words, each word consisting of 12 digits.