Accurate phase and time synchronization over packet networks is a critically important requirement in today’s mission-critical networks. Recommendation ITU-T G.8273.2 specifies the minimum clock performance requirements for telecom boundary clocks (T-BC) and telecom time synchronous clocks (T-TSC) when deployed with full timing support from the network. These performance requirements include: • Time error noise generation • Noise tolerance • Noise transfer • Transient response • Holdover performance This application note explains each of these performance requirements and assesses their relative importance to aid network operators and service providers in evaluating synchronization solutions.