The fat tree topology offers 1&colon;1 oversubscription ratio and full bisection bandwidth. Call Admission Control (CAC) prevents oversubscription of VoIP networks. Calculation and management of oversubscription ratios is common in the CATV industry. In this example, the download oversubscription ratio is 92&colon;1. This was due to massive oversubscription which led to increased admissions in that year. Oversubscription is the basis for all non-dedicated telecommunications services. In other words, oversubscription works because not everyone uses it at the same time. By 2004, the European School, Luxembourg I (ESL1) had reached oversubscription.