400-051: CCIE Collaboration Exam - Performance Monitor Clock Rates for RTP Jitter Calculation

Clock Rates for RTP Jitter Calculation

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Which two clock rates does Performance Monitor use to calculate RTP jitter values? (Choose two.)



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A. B. A. D. E. F. G. H.



The Performance Monitor tool in Cisco Unified Communications Manager (CUCM) is used to monitor the quality of voice and video calls over the network. One of the key metrics it measures is RTP (Real-time Transport Protocol) jitter, which is a measure of the variation in the delay of RTP packets as they traverse the network.

To calculate RTP jitter values, Performance Monitor uses two clock rates:

  1. The RTP timestamp clock rate: This is the clock rate used by the sending device to timestamp each RTP packet. The timestamp is used to calculate the interarrival time between packets, which is then used to calculate the jitter.

  2. The RTP audio clock rate: This is the clock rate used to sample the audio signal and generate the RTP packets. The audio clock rate is typically 8 kHz for PCMU and PCMA codecs, and 16 kHz for some other codecs.

Therefore, the correct answers to the question are:

B. PCMU (711 mu-law), 8000 Hz: This combination is a commonly used codec and audio clock rate in VoIP networks.

D. PCMA (711 A-law), 32000 Hz: This combination is also used in some VoIP networks, particularly in Europe where the A-law codec is more common than the mu-law codec.

Option G and H are not correct as they refer to the clock rates used for the H.263 video codec, which is not relevant to the calculation of RTP jitter values. Option F is also incorrect as it refers to the wrong audio clock rate for the 711 A-law codec.