I worked for Pacific Telephone (later Pacific Bell and Pacific Telesis). As telco engineers, the network was engineered to handle the peak load on Mother's Day. The circuit paths through the switches were real physical paths. The switch was treated as a server with capacity measured in hundred call seconds where an hour has 3600 seconds, a load of 36 CCS was 100% in use. The goal was to have enough capacity to avoid hitting 36 CCS. Likewise, in less busy times of the year, the goal was to keep the capital investment of the switch at around 80% utilization to earn a good return on the equipment investment. 28.8 CCS is 80%.
Modern telco switches are digital with space-time-space or time-space-time strategies along with elastic buffers and bundling data traffic on higher speed digital serial lines (optical). Mother's Day is still a peak usage day, but building capacity is much easier compared to the days of crossbar switches.