CCNP Voice FAQ: Cisco VoIP Implementations
Q1. Which one of the following is not a benefit of VoIP compared to traditional circuit-switched telephony?
A. Consolidated network expenses
B. Improved employee productivity
C. Access to new communication devices
D. Higher voice quality
Q2. Which one of the following is not considered a packet telephony device?
A. IP phone
B. Call agent
Q3. Which one of the following is not an analog interface?
Q4. Which one of the following digital interface descriptions is incorrect?
A. T1 CAS with 30 voice channels
B. T1 CCS with 23 voice channels
C. BRI with 2 voice channels
D. E1 with 30 voice channels
Q5. Which one of the following is not one of the three stages of a phone call?
A. Call setup
B. Call maintenance
C. Call teardown
D. Call processing
Q6. Which one of the following is not a step in analog-to-digital signal conversion?
Q7. Based on the Nyquist theorem, what is the appropriate sampling rate for an analog voice signal with a maximum frequency of 4000 Hz?
Q8. Which of the following accurately describes the 8-bit encoding?
A. 1 polarity bit, 3 segment bits, 4 step bits
B. 1 polarity bit, 4 segment bits, 3 step bits
C. 4 polarity bits, 3 segment bits, 1 step bit
D. 3 polarity bits, 4 segment bits, 1 step bit
Q9. Which of the following codec descriptions is incorrect?
A. G.711 PCM 64 Kbps
B. G.726 ADPCM 8 Kbps
C. G.728 LD-CELP 16 Kbps
D. G.729 CS-ACELP 8 Kbps
Q10. Which of the following is not a telephony application that requires usage of a DSP?
A. Voice termination
Q11. Which of the following is a false statement?
A. Voice needs the reliability that TCP provides.
B. Voice needs the reordering that RTP provides.
C. Voice needs the time-stamping that RTP provides.
D. Voice needs the multiplexing that UDP provides.
Q12. Which of the following correctly specifies the header sizes for RTP, UDP, and IP?
A. 8 bytes of RTP, 12 bytes of UDP, and 20 bytes of IP
B. 20 bytes of RTP, 12 bytes of UDP, and 8 bytes of IP
C. 8 bytes of RTP, 20 bytes of UDP, and 12 bytes of IP
D. 12 bytes of RTP, 8 bytes of UDP, and 20 bytes of IP
Q13. Which of the following is not a factor influencing VoIP media bandwidth?
A. Packet rate
B. Packetization size
C. TCP overhead
D. Tunneling or security overhead
Q14. If 30 ms of voice is packetized, what will the packet rate be?
A. 50 packets per second
B. 60 packets per second
C. 30 packets per second
D. 33.33 packets per second
Q15. With G.711 and a 20-ms packetization period, what will be the bandwidth requirement over Ethernet (basic Ethernet with no 802.1Q or any tunneling)?
A. 87.2 kbps
B. 80 kbps
C. 64 Kbps
D. 128 Kbps
Q16. With G.729 and 20 ms packetization period, what will be the bandwidth requirement over PPP if cRTP is used with no checksum?
A. 8 Kbps
B. 26.4 Kbps
C. 11.2 Kbps
D. 12 Kbps
Q17. Which of the following is not a factor in determining the amount of bandwidth that can be saved with VAD?
A. Type of audio (one-way or two-way)
B. Codec used
C. Level of background noise
D. Language and character of the speaker
Q18. Which of the following is not a voice gateway function on a Cisco router (ISR)?
A. Connect traditional telephony devices
B. Survivable Remote Site Telephony (SRST)
C. CallManager Express
D. Complete phone feature administration
Q19. Which of the following is not a Cisco Unified CallManager function?
A. Converting analog signal to digital format
B. Dial plan administration
C. Signaling and device control
D. Phone feature administration
Q20. Which of the following is not an enterprise IP Telephony deployment model?
A. Single site
B. Single site with clustering over WAN
C. Multisite with either centralized or distributed call processing
D. Clustering over WAN
Q21. List at least three benefits of packet telephony networks.
Answer: The benefits of packet telephony networks include these:
- More efficient use of bandwidth and equipment
- Lower transmission costs
- Consolidated network expenses
- Improved employee productivity
- Access to new communication devices
Q22. List at least three important components of a packet telephony (VoIP) network.
Answer: Following are the components of a packet telephony (VoIP) network:
- Multipoint control units
- Application servers
- Call agents
- Video end points
Q23. List three types of analog interfaces through which legacy analog devices can connect to a VoIP network.
Answer: The analog interfaces through which legacy analog devices can connect to a VoIP network include these:
Q24. List at least two digital interface options to connect VoIP equipment to PBXs or the PSTN.
- T1/E1 CAS
- T1/E1 CCS
Q25. List the three stages of a phone call.
Answer: The three stages of a phone call are:
- Call setup
- Call maintenance
- Call teardown
Q26. What are the two main models of call control?
Q27. List the steps for converting analog signals to digital signals.
Answer: The steps for converting analog signals to digital signals include the following:
- Compression (optional)
Q28. List the steps for converting digital signals to analog signals.
Answer: Following are the steps for converting digital signals to analog signals:
- Decompression of the samples, if compressed
- Reconstruction of the analog signal from PAM signals
Q29. Based on the Nyquist theorem, what should be the minimum sampling rate of analog signals?
Q30. What are the two main quantization techniques?
Q31. Name and explain the quantization methods used in North America and in other countries.
methods are quasi-logarithmic; they use logarithmic segment sizes and linear step sizes within each segment. For communication between a µ-Law and an A-Law country, the µ-Law country must change its signaling to accommodate the A-Law country.
Q32. Name at least three main codec/compression standards, and specify their bandwidth requirements.
Answer: The main codec/compression standards and their bandwidth requirements are as follows:
- G.711 (PCM)—64 Kbps
- G.726 (ADPCM)—16, 24, or 32 Kbps
- G.728 (LDCELP)—16 Kbps
- G.729 (CS-ACELP)—8 Kbps
Q33. What is MOS?
Q34. What is a DSP?
telephony applications: voice termination, conferencing, and transcoding.
Q35. Which TCP/IP protocols are responsible for transporting voice? What are the sizes of those protocol headers?
Q36. What features does RTP provide to complement UDP?
Q37. What is cRTP?
bytes (without a checksum), and to 4 bytes (with a checksum). cRTP provides significant bandwidth savings, but it is only recommended for use on slow links (less than 2 Mbps).
Q38. List at least three factors that influence bandwidth requirements of VoIP.
Q39. What is the relationship between the packet rate and the packetization period?
period is 20 milliseconds (0.020 seconds), the packet rate is equal to 1 over 0.020, or 50 packets per second.
Q40. What are the sizes of Ethernet, 802.1Q, Frame Relay, and Multilink PPP (MLP) overheads?
- Ethernet—18 bytes
- 802.1Q+Ethernet—4 + 18 = 22 bytes
- Frame Relay—6 bytes
- MLP—6 bytes
Q41. Name at least three tunneling and security protocols and their associated overheads.
Answer: Following are the tunneling and security protocols and their associated overheads:
- IPsec transport mode—30 to 53 bytes
- IPsec Tunnel mode—50 to 73 bytes
- L2TP—24 bytes
- GRE—24 bytes
- MPLS—4 bytes
- PPPoE—8 bytes
Q42. Briefly list the steps necessary to compute the total bandwidth for a VoIP call.
Answer: Following are the steps necessary to compute the total bandwidth for a VoIP call:
- Determine the codec type and packetization period.
- Gather the link information. Determine whether cRTP, any type of tunneling, or IPsec is used.
- Calculate the packetization size or period.
- Add all the headers to the packetization size.
- Calculate the packet rate.
- Calculate the total bandwidth
Q43. What is VAD?
it might result in up to 35 percent bandwidth savings. The success of VAD depends on the types of audio, the level of background noise, and other factors.
Q44. List at least three important components of enterprise voice implementations.
Answer: The components of the enterprise voice implementations include the following:
- IP phones
- Cisco Unified CallManager
Q45. List at least three voice gateway functions on a Cisco router.
Answer: On a Cisco router, voice gateway functions include the following:
- Connect traditional telephony devices
- Convert analog signals to digital and vice versa
- Encapsulate digital voice into IP packets
- Perform voice compression
- Provide DSP resources for conferencing and transcoding
- Provide Cisco survivable remote site telephony (SRST)
- Act as the call agent (Cisco Unified CallManager Express)
Q46. List the main functions of Cisco Unified CallManager.
Answer: The main functions of Cisco Unified CallManager include the following:
- Call processing
- Dial plan administration
- Signaling and device control
- Phone feature administration
- Directory and XML services
- API for external applications
Q47. List the four main enterprise IP Telephony deployment models.
Answer: The main enterprise IP Telephony deployment models are as follows:
- The single site
- Multisite with centralized call processing
- Multisite with distributed call processing
- Clustering over WAN
Q48. What is CAC?
calls to prevent oversubscription.
Q49. With QoS features in place, there can be up to ten concurrent VoIP calls over a company WAN link. Is there a need for CAC? With no CAC, what will happen when there are more than ten concurrent calls?