Topic 3 – Describe VoIP Components and Technologies

Question 6
You are CCNA VOICE associate in Lead2pass.com.  You use IP phone A to place a call to IP phone B. How many RTP streams are required for the call to be successfully completed?
A.2
B.3
C.4
D.5
Answer: A
After a call is successfully established, both ends of the calling form a virtual channel call via negotiation, using its own IP address as the IP header of the source and destination address. Therefore, a complete call must be bidirectional, that is, two RTP streams are necessary.

Question 7
Please match the protocol to the characteristic.
(1)SIP
(2)SCCP
(3)H.323
(4)MGCP
(I)Peer-to-Peer
(II)Client/Server
A.(I)-(1 2);(II)-(3 4)
B.(I)-(2 4);(II)-(1 3)
C.(I)-(1 4);(II)-(2 3)
D.(I)-(1 3);(II)-(2 4)
Answer: D
Explanation:
This question tests the classification of IP signaling.
The IP signaling can be divided into two categories: peer-to-peer and client-server.
Peer-to-peer: There are no registration relations between the terminals, terminal and call agent. It is only necessary to ensure the reachability on IP. The call establishment and parameter selection are both decided after mutual negotiation. The peer-to-peer signaling includes H323 and SIP.
Client-Server: The terminal must be registered in the call agent and all the negotiations should be completed by the call agent. The terminal completes the related action according to the direction of call agent. The client-server signaling includes SCCP and MGCP.

Question 8
Which protocol provides VoiP packet sequence numbering?
A.IP
B.TCP
C.UDP
D.RTP
Answer: D
Explanation:
This question tests the composition of voice IP packets and function of each part.
A: IP: signaling negotiation or the source and destination address of RTP media stream;
B: TCP: a layer4 protocol in H323 negotiation process. As the media stream does not require retransmission and reliability assurance, TCP will not be used as the transport protocol in the stage of the media stream.
C: UDP: With UDP, computer applications can send messages or datagrams to other hosts on an IP network without requiring prior communications to set up special transmission channels or data paths.
D: RTP: It cooperates with UDP in the transmission process of media stream and provides sequence number and time stamp for the media stream.

Question 9
Which codec is less processor intensive?
A.G729
B.G729a
Answer: B
Explanation:
G.729a is a compatible extension of G.729, but requires less computational power. This lower complexity, however, bears the cost of marginally reduced speech quality.

Question 10
What is required to convert a G711ulaw call to G729?
A.Voice Termination resources
B.Conferencing resources
C.Converter resources
D.Transcoding resources
Answer: D
Explanation:
This question tests the use of DSP Transcoding resources.
A: Voice Termination resources: MTP, mixing the two-way voice into one-way voice for the transfer applications, etc. and supporting the applications among the same coding.
B: Conferencing resources: which are applied to Meet me or Ad hoc conferences (i.e. Conference Bridge session). There is no necessity to convert if the codes are the same and vice versa.
C: Converter resources: the optimization of DSP resources and efficient utilization of DSP resources.
D: Transcoding resources: it is specifically used for transcoding and is possible to convert a G711ulaw call to G729.