Specifications

Technical Concepts Nur für den internen Gebrauch
A31003-H3580-M103-2-76A9, 01-2009
9-26 HiPath 3000/5000 V8 - HG 1500 V8, Administrator Documentation
hg-09.fm
Static and Adaptive Jitter Buffer
9.5.4 Clock Drift in Static Jitter Buffers
The measured time provides the timestamp for the packets that make up an IP-based voice
transmission. If the time measurements on the send and receive side do not exactly match,
more or fewer packets are generated on the send side than anticipated on the receive side. This
discrepancy is known as clock drift.
If more packets are generated on the receive side than anticipated in the HG board’s jitter buff-
er, more packets than expected flow into the jitter buffer. This causes a steady increase in the
measured average delay. The jitter buffer readjusts when the maximum delay value is reached.
It skips supernumerary packets until the measured average delay reaches the value set for av-
erage delay. Then the entire procedure starts again from the beginning. The following illustra-
tion shows this process:
If fewer packets are generated on the receive side than anticipated in the HG board’s jitter buff-
er, fewer packets than expected flow into the jitter buffer. This causes a steady decrease in the
measured average delay. When there are no more packets in the jitter buffer, the jitter buffer
readjusts and adapts the measured average delay once again to the value set for average de-
lay. Then the entire procedure starts again from the beginning. In this case, no packets are lost.
The following illustration shows this process:
Measured time
maximum delay (adjustable)
Legend:
average delay (adjustable)
average delay measured
Delay