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(TCO 1) The two variants of the ITU G.711 codec are _____ (Points :...

(TCO 1) The two variants of the ITU G.711 codec are _____ (Points : 5)

V-law and A-law.
T-1 and E-1.
mu-law and A-law.
None of the above

Question 2.2. (TCO 1) What’s the typical uptime percentage associated with PSTN business services? (Points : 5)


Question 3.3. (TCO 2) Which circuit-switched Private Branch Exchange (PBX) hardware connects a PBX to Central Office (CO) switches? (Points : 5)

Line cards
Trunk cards
Administrative terminal
None of the above

Question 4.4. (TCO 2) An end user of a(n) _____ uses line keys on the phone panel to select and access telephone company lines. (Points : 5)

key system
Private Branch Exchange (PBX)
Automatic Call Distribution (ACD)
All of the above

Question 5.5. (TCO 5) Which transport layer protocol is better suited for carrying real-time voice traffic in VoIP? (Points : 5)


Question 6.6. (TCO 5) In the RTP header, _____ is a random value and increments by 1 for each packet sent. (Points : 5)

time stamp
payload type
synchronization source identifier
sequence number

Question 7.7. (TCO 4) Which of the following audio codecs, in its original form, requires 8 Kbps of bandwidth? (Points : 5)


Question 8.8. (TCO 4) Which of the following audio codecs, in its original form, is best known for preserving sound quality? (Points : 5)


Question 9.9. (TCO 5) Which of the following techniques could potentially fail to reduce VoIP bandwidth consumption? (Points : 5)

Payload compression (e.g., G.729A)
Header compression (e.g., cRTP)
Silence suppression (i.e., VAD)
Large payload sizes

Question 10.10. (TCO 3) Which of the following has motivated the adaptation of VoIP technologies, especially in business environments? (Points : 5)

Reduced operational costs.
Readily available IP networking expertise.
Hybrid PBXs that help preserve the investment in existing circuit-switched equipment and also provide IP capabilities.
All of the above

Question 11.11. (TCO 6) Which SIP method/response is typically generated to signal the end of a call session or dialog? (Points : 5)

Notify (NOTIFY)
Update (UP)
Goodbye (BYE)

Question 12.12. (TCO 6) Refer to the following SIP INVITE method/request. Who is the caller?

INVITE [email protected] SIP/2.0
Via: SIP/2.0/UDP;
Max-Forwards: 70
To: John &[email protected]>
From: Mary &[email protected]>;
Call-ID: [email protected]
CSeq: 413159 INVITE
Contact: &[email protected]>
Content-Type: application/sdp
Content-Length: 142 (Points : 5)


Question 13.13. (TCO 6) In H.323 call signaling, _____ is used for terminals to exchange capabilities and preferences such as audio and video codecs during a call setup. (Points : 5)


Question 14.14. (TCO 6) A VoIP gateway translates _____ (Points : 5)

between SIP signaling and H.323 signaling.
between SIP signaling and SS7 signaling on the PSTN.
between RTP packets and PSTN bit streams.
All of the above

Question 15.15. (TCO 7) Which of the following is an ITU standard that defines international public phone numbers? (Points : 5)


Question 16.16. (TCO 7) Which of the following is a telephony feature that was made possible by VoIP? (Points : 5)

Using a DID number to directly reach a local extension without an attendant.
Inviting and bridging multiple parties into a group call.
Forwarding incoming calls to a different extension or phone number.
Using a public telephone number (E.164) to receive faxes in one’s private e-mail box.

Question 17.17. (TCO 8) What’s the name of the gateway interface/port that connects to the Central Office (CO) switch or PBX? (Points : 5)

Foreign Exchange Subscriber (FXS)
Foreign Exchange Office (FXO)
Direct Inward Dialing (DID)
Dual-tone Multi-frequency (DTMF)

Question 18.18. (TCO 8) Which of the following is typically required to connect SIP trunks to legacy PBXs and analog phones? (Points : 5)

SIP Proxy

Question 19.19. (TCO 9) 200 seconds of total holding time during the Busy Hour generates a traffic load of _____ (Points : 5)

1 Erlang.
1 CCS.
2 Erlangs.
2 CCS.

Question 20.20. (TCO 9) Given that the traffic load remains the same, which of the following call blocking probabilities will demand the least amount of trunk resources (e. g., trunk circuits)? (Points : 5)


Question 21.21. (TCO 12) _____ attacks involve large numbers of spoofed calls that overwhelm the access bandwidth or trunk capacity of a phone system. (Points : 5)

SIP scanning
Denial of Service (DoS)

Question 22.22. (TCO 12) Even if the voice traffic is encrypted, an intruder may capture and interpret _____ to discover who calls whom, when calls involve specific phones, and other information. (Points : 5)

audio codecs
voice packet payloads
call signaling messages
All of the above

Question 23.23. (TCO 11) Network connectivity is a(n) _____ a good user experience on VoIP services. (Points : 5)

guarantee of
irrelevant factor of
prerequisite to
None of the above

Question 24.24. (TCO 11) Which of the following is not correct about troubleshooting echo? (Points : 5)

The built-in echo canceling of speaker phones and those designed for audio conferencing could fail.
Although not “visible” in packets, echo can be heard when playing back audio streams.
The echo canceler feature of a gateway between VoIP and analog lines could be turned off.
None of the above

Question 25.25. (TCO 10) IEEE 802.1p defines eight priority classes for _____ prioritization. (Points : 5)

layer 2
layer 3
layer 4
None of the above

Question 26.26. (TCO 13) Which of the following is not an indicator of high-end desktop IP phones? (Points : 5)

Graphical user interface (GUI)
Color displays
Touch screens
Voice mail

Question 27.27. (TCO 13) A _____ VoIP solution typically has only phones remaining on the enterprise LAN. (Points : 5)

None of the above

Question 28.28. (TCO 13) Choose the correct formula for calculating Return on Investment (ROI). (Points : 5)

(the expected returns from a project – the amount of time required to complete the project) / the cost of implementing a project.
(the cost of implementing a project – the expected returns from a project) / the amount of time required to complete the project.
(the cost of implementing a project – the amount of time required to complete the project) / the expected returns from a project.
(the expected returns from a project – the cost of implementing a project) / the amount of time required to complete the project.

1. (TCO 5) ABC Inc. replaced its legacy circuit-switched PBX with an SIP-based VoIP system on its Ethernet LAN. When capturing and observing voice packets using Wireshark, which header contains the sequence number and time stamp information needed for playing back the audio at the receiving end? Describe, in one paragraph, how the sequence number and time stamp are used to for this purpose. (Points : 10)

Question 2.2. (TCO 5) What’s the primary factor that determines the required bandwidth per VoIP conversation? List and explain, in one paragraph, two methods that could help reduce the bandwidth consumption of a VoIP call on WAN links. (Points : 10)

Question 3.3. (TCO 6) What’s the H.323 terminology for an SIP server (or VoIP server)? Describe, in one paragraph, two tasks for which an IP phone needs to communicate with an SIP server. (Points : 10)

Question 4.4. (TCO 10) When processing an Ethernet voice frame, where in the frame does an 802.1p-enabled switch look for the priority marking? When processing an IP voice packet, where in the packet does a QoS-enabled router look for the priority marking? Describe, in one paragraph, two circumstances under which prioritizing voice traffic has little effect on its QoS guarantee. (Points : 10)

Question 5.5. (TCO 9) Use the Erlangs and VoIP Bandwidth Calculator at to complete the following question.

The IP PBX of ABC Inc. observed 120 call attempts during the Busy Hour of the WAN connection to its service provider. The average call duration was 10 minutes. What’s the traffic volume/load in Erlangs of the WAN connection?

The audio codec used on the WAN connection is G.711 with a 20-millisecond packet duration. Assume the targeted call blocking probability for ABC Inc. is 1% (i.e., 0.01). How much bandwidth (in Kbps) is required to carry the previously calculated voice traffic volume/load? (Points : 10)

Question 6.6. (TCO 11) Describe, in four paragraphs, the International Telecommunication Union’s rule for various tiers of voice transmission end-to-end latency (i.e., 150 milliseconds, 200 milliseconds, above 250 milliseconds, and above 500 milliseconds). (Points : 10)

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