Topic 3 – Describe VoIP Components and Technologies

Question 16
_____protocol is used to monitor and provide control information about the quality of an RTP session.
Answer: RTCP
Explanation:
This question is to examine the knowledge of RTCP.
The RTP Control Protocol (RTCP) is a sister protocol of the Real-time Transport Protocol (RTP). RTCP provides out-of-band statistics and control information for an RTP flow. It partners RTP in the delivery and packaging of multimedia data, but does not transport any media streams itself.

Question 17
What codec is required for fax pass-through and/or modem pass-through?
A.G.711
B.G.723
C.G.729
D.G.729ab   
Answer: A
G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. It is required standard in many technologies, for example in H.320 and H.323 specifications. It can be also used in one of methods for fax communication over IP networks.

Question 18
What protocol is used to communicate between a DSP farm configured on an IOS router and a Cisco Unified Communications Manager server?
A.H.323
B.MGCP
C.SIP
D.SCCP   
Answer: D
Explanation:
The Signalling Connection Control Part (SCCP) is a network layer protocol that provides extended routing, flow control, segmentation, connection-orientation, and error correction facilities in Signaling System 7 telecommunications networks, which is able to enable the communication between a DSP and a Cisco Unified Communications Manager server.

Question 19
What are the functions of an H.323 gateway?
A.Converts an alias address to an IP address
B.Responds to bandwidth requests and modifications
C.Transmits and receives G.711 PCM-encoded voice
D.Performs translation between audio, video, and data formats
Answer: D
Explanation:
This question is to examine the functions of the gateway.
No matter it is H323, MGCP or SIP gateway, their functions are the same. The following are the functions of the H.323 gateway.
1. the translation between mediums;
2. the translation between signaling;
3. the translation between audios or videos;
That is, the fundamental role of the gateway is to connect two different types of communication networks.

Question 20
Which call control model does MGCP use?
A.Distributed
B.Centralized
C.Ad hoc
D.Hybrid
Answer: B
Explanation:
This question is to examine the UC module applicable to MGCP.
Media Gateway Control Protocol (MGCP) is a signaling and call control protocol used within Voice over IP (VoIP) systems that typically interoperate with the public switched telephone network (PSTN). All the calls are processed by the call agent, and all the UC components must be registered in the call agent. Therefore, it is necessary to use the centralized call control model. The call agent is able to unified manage components and process calls. Choose B.