Which statement is true about the Call Admission Control （CAC） feature in VoIP networks？（）

• A、 CAC is used to allocate enough bandwidth for the number of calls that are allowed on the VoIP network.
• B、 CAC is used to protect the quality of the voice calls by preventing call establishment if enough resources are not available on the network.
• C、 CAC provides queuing mechanisms for voice calls if the packets exceed the configured or budgeted rate.
• D、 In a VoIP network the CAC can be replaced with the LLQ QoS mechanism if it has been properly implemented.