In a Teleworker deployment with a single IP phone connected to a Cisco 831 router, select the true statement regarding Call Admission Control.（）

• A、RSVP is a required configuration to support conference calls without voice packet loss. 
• B、The QoS configuration on the 831 router must always provision sufficient bandwidth for two RTP streams. 
• C、Call admission control is an issue only when using hardware DSP resources. 
• D、When using the conference call features on a 7960 IP phone, only one RTP stream is present regardless of how many extensions are on the conference.