Which of the following is most likely to cause dropped packets on a VoIP network? (Select the best answer.)
A.
congestion
B.
jitter
C.
endtoend delay
D.
variation in delay
Explanation:
Of the available choices, congestion is most likely to cause dropped packets on a Voice over IP (VoIP) network.
Dropped packets can cause clips, or breaks, in the audio stream. However, voice traffic is more tolerant of
dropped packets than of delayed packets, because a small amount of packet loss is not noticeable to the
human ear. Packet loss can be mitigated by implementing Quality of Service (QoS) and congestion avoidance
mechanisms, increasing bandwidth, and increasing buffer space. In addition, some codecs can correct small
amounts of packet loss.
Jitter is another term for a variation in delay, which causes delayed packets, not dropped packets. Jitter can
cause packets to arrive out of sequence or at a different rate than they were sent. VoIP traffic is heavily affected
by jitter because voice traffic is timesensitive and requires that the destination host receive the voice traffic in
the order, and at the same rate, it was sent. When jitter is present, the end user might experience choppiness
in the audio connection. A dejitter buffer at the destination is used to collect packets, sort them into the proper
sequence based on Realtime Transport Protocol (RTP) time stamps, and release them to the voice application.
Although a dejitter buffer can decrease jitter, it can increase delay as packets sit in the buffer. Jitter can be
mitigated by increasing bandwidth, using QoS mechanisms to prioritize time-sensitive traffic, using
Compressed RTP (cRTP) to compress headers, and using Stacker and Predictor to compress payloads.Endtoend delay causes delayed packets, not dropped packets. Endtoend delay is the sum of the processing,
queuing, serialization, and propagation delays in the traffic path between the source of the packet and the
destination of the packet. Therefore, the total network delay between the source of the packet and its
destination is considered endtoend delay. Endtoend delay can be mitigated by QoS mechanisms.https://www.cisco.com/c/en/us/td/docs/ios/12_2/qos/configuration/guide/fqos_c/qcfconav.html#wp1003370