Go back to 640-460 - IIUC Implementing Cisco IOS Unified Communications (IIUC)

Question :-

Which Cisco Unified Communications layer is the call processing layer?
Layer A including video,communications client, software-based phones, IP Phone
Layer B including Voice mail,Presence,Contact Center
Layer C including Cisco Unified Communications manger,Directory Server.
Layer D including Gateway, Router, Switch.

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