Which of the following are methods are supported by SIP Server for detecting whether a particular device is unavailable and needs to be placed in Out of Service state? (Choose 2 answers)

Which of the following are methods are supported by SIP Server for detecting whether a particular device is unavailable and needs to be placed in Out of Service state? (Choose 2 answers)
A . Active out of service detection
B . Passive out of service detection
C . Auto out of service detection
D . Presence subscription
E . Registration
F . class of service

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Answer: D,E