Cisco 400-051 Exam

Which two SCCP call signaling messages are initiated by Cisco Unified Communications Manager to an IP phone? (Choose two.)

  • A. SoftKeyEvent
  • B. CloseReceiveChannelAck
  • C. CallState
  • D. KeypadButton
  • E. OpenReceiveChannel
  • F. Offhook
Answer: Option C. E.
Explanation: 

Upon receiving an OpenReceiveChannelmessage, the IP phone selects the UDP port number it wants to use to receive RTP packets and reports this information to call manager.
With the SCCP protocol architecture, the majority of the H.323 processing power resides in an H.323 proxy — the Cisco CallManager. The end stations (IP phones) run the Skinny client, which consumes less processing overhead. The client communicates with CallManager using connection-oriented (TCP/IP-based) communication to establish a call with another H.323-compliant end station. Once Cisco CallManager has established the call, the two H.323 end stations use connectionless (UDP/IP-based) communication for audio transmissions.

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