NETW 250- Final Exam

1. (TCO 1) ITU recommendation G. 711 is also referred to as _____ (Points : 5)

Mean Opinion Score (MOS).

Pulse Code Modulation (PCM)

Digital Signal (DS)-0 channel.

DS-1 channel.

Question 2.2. (TCO 1) What’s a typical amount of downtime associated with PSTN business services? (Points : 5)

Several days per year

Several hours per year

Several minutes per year

Several seconds per year

Question 3.3. (TCO 2) Which circuit-switched Private Branch Exchange (PBX) hardware allows internal phones and extensions to be connected to the PBX? (Points : 5)

Line cards

Trunk cards

Administrative terminal

Voice mail card

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 not used by voice packets in VoIP? (Points : 5)

UDP

TCP

RTP

Question 6.6. (TCO 5) In the RTP header, _____ is used by the receiver to detect lost packets and to ensure that received packets are played back in proper order? (Points : 5)

time stamp

payload type

sequence number

synchronization source identifier

Question 7.7. (TCO 4) Which of the following audio codecs, in its original form, requires 64 Kbps of bandwidth? (Points : 5)

G.728

G.711

G.723.1

G.729A

Question 8.8. (TCO 4) Which of the following audio codecs, in its original form, requires the least amount of bandwidth? (Points : 5)

G.711

G.728

G.723.1

G.729A

Question 9.9. (TCO 5) Which of the following techniques help reduce VoIP bandwidth consumption? (Points : 5)

Payload compression (e.g., G.729A)

Header compression (e.g., cRTP)

Large payload sizes

All of the above

Question 10.10. (TCO 3) Which of the following VoIP equipment is typically seen in a residential environment? (Points : 5)

Hybrid Private Branch Exchange(PBX)

VoIP server

IP Private Branch Exchange(PBX)

An IP phone that connects to a broadband router

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

INVITE (INV)

Notify (NOTIFY)

Update (UP)

Goodbye (BYE)

Question 12.12. (TCO 6) Which SIP method/request or response is shown below?

INVITE sip:john@abc.com SIP/2.0

Via: SIP/2.0/UDP pc14.chicago.com;branch=z9hG4bK887chdhds

Max-Forwards: 70

To: John <sip:john@abc.com>

From: Mary <sip:mary@chicago.com>;tag=1982301747

Call-ID: a48b4c67e77610@pc14.chicago.com

CSeq: 413159 INVITE

Contact: <sip:mary@pc14.chicago.com>

Content-Type: application/sdp

Content-Length: 142 (Points : 5)

Notify

200 OK

Acknowledgment

INVITE

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)

H.225

SIP

H.245

RTCP

Question 14.14. (TCO 6) Which of the following is not a typical function of VoIP gateways? (Points : 5)

Converting between RTP packets and PSTN voice bit streams.

Registering terminals or User Agents (UAs).

Converting VoIP signaling and SS7 signaling on the PSTN.

Converting between different audio codecs (i.e., voice transcoding).

Question 15.15. (TCO 7) Which of the following facts about Local Number Portability (LNP) is not correct? (Points : 5)

When switching from TDM service to VoIP, subscribers don’t have to give up their previous telephone numbers.

The LNP policy doesn’t apply to toll-free numbers.

Cellular telephone numbers are portable under certain conditions.

LNP is only a U.S. national policy.

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 an analog phone? (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)

Gatekeeper

Softswitch

SIP Proxy

Gateway

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 targeted call blocking probability remains the same, which of the following PBX systems will support the least amount of traffic during the Busy Hour? (Points : 5)

A PBX system with 24 trunk circuits.

A PBX system with 12 trunk circuits.

A PBX system with 8 trunk circuits.

A PBX system with 6 trunk circuits.

Question 21.21. (TCO 12) Sending an INVITE message to every phone number on a network in search of vulnerable devices based on received responses is referred to as _____ (Points : 5)

SIP scanning.

Vishing.

High-volume calling.

Eavesdropping.

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 echo in a voice call? (Points : 5)

It could be caused by acoustic feedback from a phone or headset.

It could be caused by gateways between VoIP and analog lines.

It is not “visible” in voice packets.

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 could be an indicator of high-end desktop IP phones? (Points : 5)

Touch screens

Monochrome displays

Navigation buttons

Speakers

Question 27.27. (TCO 13) Having a third-party assume all PBX management responsibilities is referred to as a(n) _____ solution. (Points : 5)

hybrid PBX

hosted PBX

on-site PBX

IP PBX

Question 28.28. (TCO 13) What does this formula calculate?

(the expected returns from a project – the cost of implementing a project) / the amount of time required to complete the project. (Points : 5)

Call For Proposal (CFP)

Payback time period

Total Cost of Ownership (TCO)

Return on Investment (ROI)

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) The IT department of ABC Inc. decides to use the G. 711 codec on its local VoIP telephony network. What’s the payload bit rate of G. 711? What does the payload bit rate mean? Explain, in one paragraph, how increasing and reducing the payload size of voice packets affects the required bandwidth per VoIP conversation, respectively. (Points : 10)

Question 3.3. (TCO 6) Explain, in a couple of paragraphs, the origin and history of the SIP protocol and the H.323 protocol suite. What are the most noticeable characteristics of each? What are some of their cons? (Points : 10)

Question 4.4. (TCO 10) Explain, in one paragraph, layer 2 prioritization and its priority classes. Explain, in one paragraph, layer 3 prioritization and its precedence levels. If a company plans to switch to VoIP, what should the IT department look for in the switches and routers on its network? (Points : 10)

Question 5.5. (TCO 9) Use the Erlangs and VoIP Bandwidth Calculator at http://www.erlang.com/calculator/eipb/ to complete the following question.

ABC Inc. is planning to lease a 512 Kbps frame relay connection between two PBXs from two branch locations. The audio codec used on the trunk is G.729A with a 20-millisecond packet duration. Assume the targeted call blocking probability for ABC Inc. is 1% (i.e., 0.01). How much traffic volume/load (in Erlangs) can this trunk support?

120 call attempts, with an average call duration of 10 minutes during the Busy Hour have been observed on the connection. What’s the current traffic volume/load (in Erlangs) on this trunk connection? Compare the current traffic volume/load to the supported traffic volume/load calculated above. Does the frame relay trunk have enough capacity to support the current traffic volume/load? (Points : 10)

Question 6.6. (TCO 11) ABC Inc. is re-evaluating the end-to-end delay budget of its cross-country VoIP services. In one paragraph, name at least two components (i.e., devices or processes) that contribute to the end-to-end latency budget.

Suggest, in one paragraph, two methods that could help ABC Inc. reduce the end-to-end delay of its cross-country VoIP services. (Points : 10)