QUESTION 1 ATM interface discards a fragment?
A. Incomplete data packets are sent and the entire data packet must be resent.
B. The entire data packet is discarded at the ingress interface and must
be resent.
C. Incomplete data packets are sent and the discarded packet fragments must
be resent.
D. Data packets may be sent in cells that are out of order, causing the entire
packet to be resent. Answer: D
QUESTION 2 Why do real-time applications like VoIP require better service than traditional
best effort services? (Choose three)
A. These applications are sensitive to jitter.
B. These applications are sensitive to delays.
C. Real-time applications are sensitive to packet drops.
D. Real-time applications are typically non-interactive and use mostly bulk
data transfer.
E. Real-time applications typically require RSVP which cannot be run on a
network using best-effort services. Answer: A, B,
C Explanation: Quality of Service is usually identified
by the following parameters: Amount of bandwidth available
to a certain application or user Average delay experienced
by IP packets on end-to-end or link basis Jitter that
affects applications that transmit packets at a certain
fixed rate and expect to receive them at approximately
the same rate (for example, voice and video) Drops
of packets when a link is congested can severely impact
fragile applications Admission control which prevents
too many sessions from congesting links and causing
degradation in quality of service (for example, voice
sessions) Source: Cisco IP QoS Introduction, Page
4
QUESTION 3 Which statement is true about policing traffic conditions in IP QoS?
A. Policing reorders transmit queues to offer priority service to specific
traffic flows.
B. Policing utilizes buffers to delay excessive traffic when the flow is
higher than expected.
C. Policing techniques monitor network traffic loads in an effort to anticipate
and avoid congestion.
D. Policing allows the network administrators to traffic engineer paths through
the network for application flows.
E. Policing is the ability to control bursts and conform traffic to ensure
certain traffic types receive specified amounts of bandwidth. Answer: C Incorrect:
B. Policing does not introduce any delay to traffic that conforms to traffic
policies
E. With shaping, traffic bursts are smoothed out producing a steadier flow
of data Explanation: The QoS tool used to monitor the rate, and discard the excess traffic,
is called traffic policing, or just policing. Because the provider is monitoring traffic sent by the customer, traffic
polices typically monitor ingress traffic, although they can monitor egress traffic as well. Source: Cisco DQOS Exam Certification Guide, Page 95
QUESTION 4 What is a limiting factor of IntServ scalability in large networks?
A. IntServ admission control must be implemented locally on all the routers.
B. MPLS/TE tunnels cannot be established through an MPLS network using RSVP.
C. IntServ requires the routers to track a large amount of per-flow state
information.
D. IntServ requires all the routers to identify common flows that require
the same service into a traffic aggregate.
E. The IntServ QoS mechanism used to apply the appropriate per-hop behavior
(PHB) must be implemented on all the routers. Answer: C Explanation: Benefits and Drawbacks of the IntServ Model The main drawbacks of RSVP
are: Continuous signaling due to stateless operation of RSVP. RSVP is not scalable to large networks where per-flow guarantees would
have to be made to thousands of flows. Source: Cisco IP QoS Introduction, Page 30
QUESTION 5 Which three Cisco IOS QoS mechanisms have marking capabilities? (Choose
three)
A. PBR
B. Committed Access Rate (CAR)
C. Weighted Random Early Detection (WRED)
D. QoS Policy Propagation through BGP (QPPB)
E. Class-Based Weighted Fair Queuing (CBWFQ) Answers: A, B, D Explanation:
This
module describes the two QoS mechanisms that are
used purely for classification and marking purposes:
Policy-based Routing (PBR) QoS Policy Propagation
through BGP ( QPPB) There are other QoS mechanisms that also support classification and marking: Committed Access Rate (CAR)
- this mechanism is described in the "IP QoS - Traffic
Shaping and Policing" module Class-based Policing (CB-Policing) - this mechanism is described
in the "IP QoS - Modular QoS CLI (Chapter 2)" module
Class-based Marking (CB-Marking) - this mechanism
is described in the "IP QoS - Modular QoS CLI (Chapter
2)" module Source: Cisco IP QoS Classification and
Marking, Page 2-3
QUESTION 6 How does Low Latency Queuing (LLQ) differ from IP Real-Time Transport
Protocol (RTP) priority?
A. LLQ is not limited to defining traffic flows using UDP port numbers.
B. IP RTP Priority can specify traffic matches based on DSCP whereas LLQ
cannot.
C. LLQ is well suited for voice traffic that is not supported in IP RTP Priority
configurations.
D. LLQ priority queues suffer from "starvation" of low priority traffic due
to preferential treatment of the high priority queue.
Answer: A Explanation:
IP
RTP Prioritization is an add-on to WFQ to support
low-delay propagation of packets. It can be used
for UDP traffic only. IP RTP Prioritization also polices the high priority traffic
to prevent starvation of other queues. Source: Cisco Queuing Mechanisms, Page 3-134
QUESTION 7 What are two important benefits of applying QoS to IP networks? (Choose
two)
A. QoS manages packet loss during periods of bursty congestion.
B. QoS allows network managers to control usage patterns of network applications.
C. QoS can solve traffic problems on low bandwidth, high-latency, high-loss
WAN links.
D. QoS facilitates the integration of differing traffic types such as voice,
video, and data into a single infrastructure.
E. QoS can provide performance enhancements for commercial application issues
such as server sizing and tuning. Answer: C, D
QUESTION 8 What allows the Differential Services model to be scaled to large networking
environments?
A. Differential services are accomplished through hop-by-hop application
signaling.
B. The Differentiated Services model scales by providing per-flow state visibility
to the core of the network.
C. Policing is not used in the Differentiated Services model providing for
efficient expediting of high priority traffic flows.
D. It achieves scalability by implementing complex classification and conditioning
requirements only at network boundary nodes.
E. In the Differentiated Services model, an explicit setup mechanism predefines
all QoS parameters for the packet before it is transmitted.
Answer: D Incorrect:
A. Core only performs simple 'per-hop behavior's' on traffic aggregates
No per-flow/per-application state in
the core Explanation: Source: Cisco IP QoS Introduction, Page 34
QUESTION 9 Exhibit: interface Serial 0/1/0 ip address 10.1.1.1 255.255.255.0 random-detect Based on the configuration in the exhibit, which statement is true?
random-detect precedence 0 1 2 1
random-detect precedence 0 10 20 10
random-detect precedence 2 15 20 10
random-detect precedence 3 20 30 10
random-detect precedence 4 25 30 10
random-detect precedence 5 30 40 10
random-detect precedence 6 35 40 50
random-detect precedence 7 35 40 100
random-detect exponential-weighted-constant
11
The drop probability of precedence 0
traffic is 100%.
The drop probability of precedence 1-5
traffic is 100%.
The drop probability of precedence 6
traffic is 100%.
The drop probability of precedence 7
traffic is 100%. Answer: A Explanation:
This configuration excerpt shows the implementation
of the dropping policy, illustrated by the case
study. The threshold values reflect the values
chosen in the previous figure. Note that precedence
4 is not used to mark traffic in the case study
network, so the drop probability of precedence
4 traffic is 100% (1 divided by 1 times 100%).
Source: Cisco Congestion Avoidance, Page 5-30
QUESTION 10 What is an important advantage of using Flow-based WRED (FRED) instead
of standard Weighted Random Early Detection (WRED)?
A. In Cisco IOS, FRED is easier to configure than WRED.
B. FRED can classify packets using DSCP and WRED cannot.
C. FRED adds support for new protocol and traffic types including UDP.
D. With FRED, packets are not dropped indiscriminate of the kind of flows
to which the packets belong. Answer: D Explanation:
FRED therefore has substantial benefits
compared to WRED, as it can also be used in
environments that do not exhibit a predominantly
TCP-based traffic mix. FRED enables differentiated
dropping between fragile and non-adaptive flows,
in which the loss rate is higher with non-adaptive
flows. This is something that WRED is unable
to do, because it drops packets without regard
to flow buffer usage. Therefore, FRED protects
fragile and adaptive flows from non-adaptive
flows, which may, in the case of RED, monopolize
router queues in their path. Source: Cisco Congestion
Avoidance, Page 5-48
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