The Exam for Nortal Certification NCTS
Published on 04/24,2009
NCTS - Converged IP Telephony Solutions
This certification validates your understanding of the standards and protocols associated with planning, designing and deploying converged IP solutions.
This certification tests your knowledge and skills in the following areas:- Major Components of VoIP
- VoIP Network Design Considerations
- Transport and Session Layer Technologies
- Implementing Quality of Service
- WLAN Convergence Issues
- VoIP Standardization and Signaling Protocols
Exams for this Certification -- Technology Standards and Protocols for IP Telephony Solutions 920-803
920-803 Technology Standards and Protocols for IP Telephony Solutions
Exam Objectives:- Major Components of VoIP (18% of Exam)
- VoIP Network Design Considerations (42% of Exam)
- Transport & Session Layer Technologies (12% of Exam)
- Implementing Quality of Service (10% of Exam)
- WLAN Convergence Issues (4% of Exam)
- VoIP Standardization & Signaling Protocols (14% of Exam)
Sample Exam Questions:
- Which VoIP network component converts one media stream to another and can interact with call controllers, proxies, and soft switches via proprietary or standard protocols such as SIP?
- A. H.323 Gateway
- B. Gatekeeper
- C. Media Gateway
- D. SIP Registrar/Proxy
B. C is the correct answer. The Media Gateway performs the following: 1. Converts one media stream to another; for example, converts voice packets to analog. 2. Can interact with call controllers, proxies, and soft switches via proprietary or standard protocols such as SIP.
- Identify the VoIP system component that performs the following functions:
receives call setup request messages.
determines the status of destination devices and checks the authorization of users to originate or receive calls.- A. Call Server
- B. Gatekeeper
- C. Media Server
- D. SIP Proxy/Registrar
B. A is the correct answer. Call Server performs the following: 1. Receives call setup request messages. 2. Determines the status of destination devices and checks the authorization of users to originate or receive calls. 3. Creates and sends the necessary messages to process the call requests.
- A WAN customer has an access link between two Private Branch Exchange (PBX) systems. The access link has sufficient bandwidth to support only two VoIP calls. When a third call is connected, voice quality of all three calls is impaired.
To prevent this problem, the customer wants to enable a gateway to reject traffic when a defined threshold is reached.
Which feature will provide this functionality?- A. Gate Threshold (GT)
- B. Call Auto Limit (CAL)
- C. Call Threshold Rejection (CTR)
- D. Call Admission Control (CAC)
C. D is the correct answer. CAC lets a gateway or gatekeeper reject traffic when a defined threshold is reached. After the call is rejected, the originating gateway must find another means of handling the call. Several possibilities exist and most are dependent on the configuration of the gateway.
- An engineer is designing a VoIP solution for a customer and has the following requirements for the speech CODEC:
best balance of voice quality and bandwidth savings
works well in WAN applications
near toll quality voice
silence suppression or Voice Activity Detection (VAD) in the transmission of voice communications
Which CODEC should the engineer select to best meet these requirements?- A. G.711
- B. G.729A/B
- C. G.726
- D. G.723.1
C. B is the correct answer. The G.729A/B is intended for low bandwidth connections, such as WAN and provides the best balance of voice quality and bandwidth savings. It requires less bandwidth than G.711 and delivers near toll quality voice. Uses silence suppression or Voice Activity Detection (VAD) in the transmission of voice communications that can further reduce bandwidth requirements.
- A technician is troubleshooting a serialization delay issue on a customer's WAN. To try to improve network performance, the technician decides to reduce the Maximum Transmission Unit (MTU) size.
What effect will this action have on the network?- A. more data will be put on the network
- B. less data will be put on the network
- C. voice quality will improve
- D. network performance and voice quality will improve
A is the correct answer. You can change the default MTU, if appropriate; however, reducing the MTU can put more data on the WAN sooner and is not necessarily as efficient. A trade-off exists between improved network performance and voice quality.
- Which echo control device has the following characteristics?
detects a signal on the incoming or outgoing path
switches attenuation into the other path to reduce the level of any returning signal- A. Echo Switcher
- B. Echo Canceller
- C. Echo Eliminator
- D. Echo Suppressor
D. D is the correct answer. An echo suppressor, or voice switch, is a device that detects a signal on the incoming or outgoing path and switches attenuation into the other path to reduce the level of any returning signal. This suppression technique can be used in speakerphones, headsets, and wireless handsets.
- A customer is operating in an Ethernet environment. As utilization has increased, the customer has been experiencing unpredictable delays between packets due to network collisions.
At a minimum, at which Layer should the customer deploy switches at both end points to avoid collisions?- A. Layer 1
- B. Layer 2
- C. Layer 3
- D. Layer 4
D. B is the correct answer. At a minimum, Layer 2 switching is required at both end points to avoid network collision.
- A designer has selected User Datagram Protocol (UDP) instead of Transmission Control Protocol (TCP) for a VoIP application.
What rationale supports this decision?- A. the application requires flow control and error recovery
- B. the application requires a Layer 5 Session protocol
- C. the application requires a Layer 4 connection-oriented protocol
- D. the application has voice and multimedia traffic and delay must be minimized
D. D is the correct answer. UDP is well-suited to VoIP traffic, such as voice and multimedia, because it lacks many of the features of TCP that introduce delay, such as flow control and error recovery. Rather than retransmitting lost packets, UDP discards the packets.
- Select the protocol with the following characteristics:
set asides the amount of bandwidth required for a transmission
uses a routing protocol for decision making
works with IPv4 and IPv6
allocated on a first-come, first-served basis- A. H.323
- B. DiffServ
- C. RSVP
- D. 802.1p
C. C is the correct answer. Resource ReSerVation Protocol (RSVP) reserves bandwidth and other resources on RSVP-compliant routers located throughout the network. RSVP is allocated on a first-come, first-served basis and ties up the amount of bandwidth needed for the transmission. RSVP depends on a router's routing protocol for decision-making. RSVP works with both Internet Protocol version 4 and Internet Protocol version 6 (IPv6), which is now included as part of IP support in many products including the major computer operating systems.
- A customer has implemented a VoIP solution over a Wireless LAN (WLAN). They are reporting that the WLAN throughput is about 50 percent of its rated speed.
What is the likely reason for this result?- A. Back-off timers and ACK packets have added overhead to the WLAN.
- B. Radio Frequency signals are distorted or blocked by an obstacle within the WLAN.
- C. Denial of Service (DoS) attacks have created WLAN instability.
- D. The WLAN is directly connected to the wired LAN, making all ports accessible to hackers.
C. A is the correct answer. LAN components use positive acknowledgement (ACK) packets to confirm that data arrived safely. If a sending station does not receive an ACK for the frame it sends, it assumes that the data did not arrive and sends the data again. The use of back-off timers and ACK packets can cause a great deal of overhead on a WLAN. This process is one of the main reasons that WLANs achieve a throughput of roughly 50 percent of their rated speed.
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